Stacked images of the comet, photobombed by Starlink satellites | Hacker News Reader

Stacked images of the comet, photobombed by Starlink satellites

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249 points_Microft204 comments

It's trivial to erase these things from photos. The photographer no doubt knows this, but that isn't the point.

It's perfectly reasonable for scientists to want to capture accurate data on the space surrounding the main subject being imaged. Simply erasing the satellites from photos does not recover the data on the space behind. Any data from behind the satellites is lost forever. This photo keeps the satellites in order to visually demonstrate this problem.

Remember that astronomy today is often done on a single pixel of data. Starlink blocks multiple pixels, and even ruins entire exposures when they flare up. This will make astronomical research, like searching for exoplanets, far harder and more expensive than it is today. Space telescopes are, and will always be, orders of magnitude more expensive than ground telescopes to launch, maintain and operate.

Starlink will provide an immediate benefit to humanity, the astronomy performed otherwise, won't. Looking for exoplanets isn't a practical concern for humanity any time soon.

Odd perspective when defending technology from the same guy that wants to save humankind by literally colonizing other objects in space.

Not necessarily- exoplanets beyond our solar system really aren't going to be feasible to physically travel to until we can come up with something along the lines of faster-than-light travel. Given the lack of light pollution on Mars, I almost wonder if we wouldn't be better off doing all of our astrophysical study out there or in deep space anyway (assuming we have a steady supply of transit back and forth to transfer the data since streaming isn't likely to have good enough quality for a long time either).

Then again, I am also not a fan of putting more satellites into orbit either... mostly just struck by your comment as being not terribly odd to me.

Ofcourse astrophysical study works better in soace, but who is oaying the added cost of launching telescioes to space?

Travelling to exoplanets is not hard, it just takes 1000 - 10,000 years.

There will be no FTL untill we can manipulate black holes, if ever at all.

So the first trip to exoplanels will be in a multi-hundred year hybernation, or a genration ship, or people that are so different from us that they don't mind the journey.

Exposures are generally taken frequently enough that any that would be problematic for data can simply be dropped. The satellites aren't permanently positioned in the sky. Geostationary satellites permanently lose any data behind them (although I haven't heard of a geostationary satellite being positioned precisely problematically).

Searching for exoplanets moving in front of a star, involves measuring the luminosity of a single pixel for ~1% change. Dropping frames ruined by a satellite train isn't going to work. E.g https://www.sciencealert.com/a-bunch-of-potential-tabby-s-st...

You absolutely can drop those frames. Exoplanetary transits are generally in the range of 1 to 4 hours, and hundreds of exposures may be taken in that time. In my undergraduate I studied astronomy and some of my classmates did an exoplanet detection project with a 61" scope and had issues with satellites on a handful of frames. Sure, it sucks to lose 2 minutes worth of data, but it's not even lose to catastrophic when you have the data before and after as well.

Absolute bunk. As numerous people have tried to explain in this thread (along with its frequent predecessors), anything that moves across frames is by definition unimportant when stacking images. It's literally the difference between integration and differentiation.

Satellites move fast. Not only that, but you know exactly where and when they will cross your field of view, and for how long they'll remain within it. If the astronomy community can't muster the rudimentary image processing technology needed to reject satellites and other transient objects, I'm not exactly confident in their ability to finally figure out the whole origin-of-the-Universe thing.

So if someone decides to make money with a byproduct being messing with your day job, you’d just shrug it off?

If I were that incompetent at my day job, I imagine quite a few people would be "messing" with me, possibly for the sheer amusement of it.

Suppose your job comes and goes with the whims of a grant or funding committee, so every last dollar you spend having to compensate for some other guy's scheme.

Science is not just difficult because the research being done is hard; it's also difficult because everything you're trying to do is being done in spite of the fact 95% of the rest of the world could give a care leas that you're doing, so that last 5% of support you can count has to go a long way.

I can understand the bitterness perfectly, and to be frank, your response is exactly the reason they deserve to be irate.

So why should a goal like truly universal Internet access play second fiddle to astronomical considerations, when the technical solutions required for coexistence are so trivial?

(And I really couldn't care less how many astronomers disagree with the assertion that it's trivial to avoid interference to observations from satellite passes. If I want to know something about astronomy, I'll ask an astronomer. Astronomers, by the same token, should consult digital imaging experts before concluding that the rest of the world is out to wreck their careers with unreasonably-expensive or technically-insurmountable roadblocks. You guys can afford to lose a frame or two now and then in exchange for what Starlink offers the rest of humanity.)

For one a Starlink satellite, or any LEO satellite, is moving really fast relative to a ground based telescope. It'll occult any given star for a fraction of a second.

If you're doing a narrow field long exposure with tracking, that will be problematic and you'll loose data. Most scientific observations don't do long exposures, especially measuring highly variable things like exoplanet transits.

It's more effective to stack a large number of short exposures for scientific measurements. It's much easier to eliminate noise because everything that is not noise will be transient for a single frame in the stack. You can also remove frames with things like satellites, clouds, or airplanes without losing much data.

Knowing the ephemeris of satellites also allows observations to time short exposures to avoid occultations. Astronomers have been dealing with satellites, clouds, and airplanes for a long time. Amateur astronomers might have a harder time with Starlink satellites but they will adapt just like they did with the ISS and Iridium.

"Members of the LSST science team said last month that, assuming the full deployment of SpaceX’s Starlink satellites, nearly every exposure from the observatory within two hours of sunset or sunrise would have a satellite streak. During summer months, when twilight times longer, there could be a 40 percent impact on twilight observing time, according to the Association of Universities for Research in Astronomy, or AURA, which manages the LSST project for the National Science Foundation.

“Because of scattered light in the optics by the bright satellites, the scientific usefulness of an entire exposure can sometimes be negated,” AURA said in a statement last month. “Detection of near-Earth asteroids, normally surveyed for during twilight, would be particularly impacted. Dark energy surveys are also sensitive to the satellites because of streaks caused in the images. Avoiding saturation of streaks is vital.”"

https://spaceflightnow.com/2019/12/09/spacex-to-experiment-w...

They're trying to do a logical OR for all the light that comes in during a long exposure, as in an old film camera with a long shutter time.

That may have worked with analog film before we had satellites, but Starlink is just the latest and brightest addition to the sky that makes that an increasingly bad idea. Change is hard, but it's not that difficult.

Instead, AND a bunch of shorter exposures. Then, your streaks are not streaks, but a series of point sources that can be removed trivially.

And who will pay for all those necessary changes? Keep in mind that this is complex stuff, you don't just hack a perl script and be done with it. Anybody who thinks it's that simple is suffering full-blown Dunning-Kruger.

If I poo in your front yard, would you be happy with me telling you simply "well you can just remove it, what's the big deal?" Or rather, pooing regularly somewhere on a lawn in a public park that you really like and visit daily.

This concern has already been addressed by SpaceX. It's worth noting that LSST is the single telescope most affected by Starlink. Since the article you posted was published, SpaceX met with the LSST people and specifically designed a sunshade to reduce the brightness of Starlink satellites on station below the threshold that will cause saturation problems. https://www.spacex.com/updates/starlink-update-04-28-2020/

>Most scientific observations don't do long exposures

Not quite the whole truth, I think you're speaking a tad beyond your expertise. While you're right that transient science generally does short exposures (TESS is 2 seconds, Kepler was 6.5, LSST will be ~20 iirc), the vast majority of astrophysical science I've been exposed to (mechanical engineer at an astrophysics research institute), 10 or 20 minute exposures are more the norm. Especially when looking at faint objects.

Doesn't take away from your main point - astronomers will adapt. I think they're perturbed by this because Starlink makes their jobs even more complex, and thus more expensive. A cost that SpaceX doesn't bear at all.

I looked up the exposure times for transient searches and went with that. It matched what astronomer friends had told me. I am not an astrophysicist.

I think astronomers have a right to be perturbed about Starlink et al. SpaceX seeming to not care about the effect Starlink satellites would have on astronomy is ridiculous. At the same time stupid mis/disinformation like this tweet is also ridiculous.

This is completely incorrect. The data is not lost, when you stack images the low signal of a single (or multiple) satellites in a single image disappears into the noise.

> The data is not lost

point me to the data behind the occlusion on a single frame.

There’s no sats up north...

If the images are stacked, doesn't that mean that there's plenty of images with the parts that are occluded in others not occluded?

I understand for any specific image, there's going to be some lost background because of Starlink satellites, but that's not what this is showing, this is showing something that's not possible, right? Shifting all the satellites temporally so they appear together, arbitrarily maximizing the problem beyond what is real isn't an accurate depiction of the problem, IMO.

Put another way, if you erase the Starlink satellites from the images before stacking them, you then get a fairly accurate representation of the sky without any Starlink satellites, and you still have the data behind them (from the other pictures where that portion of the sky was not occluded). You can also probably fix the intensity of anything occluded in a few of the pictures but not others through some math.

> If the images are stacked, doesn't that mean that there's plenty of images with the parts that are occluded in others not occluded?

As he mentioned, flare can cover a broader area of the sensor.

There's still many other images that the flare isn't affecting that area at all though, right? The point is that there's many different images used here, and instead of combining them in a way to remove transient artifacts, which is the norm, they combined them in a way to emphasize transient artifacts, which is not something people normally would want to do.

It's worse than any single image that's used to make it, so why make it at all?

It's an interesting way to demonstrate the density of the satellites- they're not hiding the number or duration of images, so you can get a fuzzy intuition for how likely you are to catch them in a given image.

Except you're not actually demonstrating the density. That could have been one satellite if you exposed long enough.

It's like taking a picture of the one car every day driving on some empty road and then coadding them and claiming you're demonstrating density of traffic.

what if the research requires long/multiple exposures.

If I understand correctly the satellites would be much dimmer there, but otherwise you'd see the same problem - correct me if I'm wrong.

Not an actual astronomer, but somewhat aware of detector issues for space-based telescopes.

Typically, you want to use one single integration time, if possible. Doing so can limit readout noise, for one thing. (Note that ground-based astrophotographers, with consumer cameras, often take multiple exposures to cool down the detectors. This is not a factor with the actively-cooled detectors in astronomical telescopes.)

For instance, the observations leading to the recent discovery of the two-planet exosystem [1] used roughly 15-minute integration times [2, sec. 2] across an 8 meter (!) aperture. This is a longer integration time than the 17, 30-second integrations that produced OP.

I think the above considerations about stacking vs single exposures are a side issue, though.

The saving grace is that many astronomical observations are narrow-field-of-view, and are done away from the illuminated part of the StarLink constellation. But, surveys or wide-field images could really be affected strongly, at the 30-40% level [3].

[1] https://news.ycombinator.com/item?id=23917559

[2] https://academic.oup.com/mnras/article/492/1/431/5680498

[3] https://www.eso.org/public/archives/releases/sciencepapers/e...

There are plenty of amateurs using actively cooled specialized astrophotography cameras with total integration times reaching hours (2-3 are typical). Readout noise can be cancelled by taking so called bias frames. Shorter exposures are sometimes preferable because of the light pollution and to minimize the possibility of an exposure being rendered usles by some plane or satellite: it is less painful to throw away three minutes of exposure time than 15.

> Readout noise can be cancelled by taking so called bias frames.

That’s not what bias frames [1] are doing. Bias frames measure a systematic effect in the conversion of stored charge to a digital number in the CCD device. You can then subtract it out.

The calibration offered by bias frames does not fix readout noise, which is a random, not systematic, effect that is inherent in the same conversion.

You can use the bias frames to compute the strength of the readout noise (i.e., the rms magnitude of its random part) but you can’t remove the random noise itself.

See sec. 1.1 of the linked reference for more.

[1] https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf

The point of bias frames is what you take them without accumulating any charge. Well yes, you cannot eliminate random noise, but you can reduce it. Also, most popular deidcated astrophotography cameras are now CMOS not CCD and readout differs in these. Your link does not work, and probably for the better. See this instead: https://www.youtube.com/watch?v=O6oGyFlZgAc

Anec-data, but in my shots of the comets there were 0 satellites and about 12 airplanes with flashing lights that I had to remove. ¯\_(ツ)_/¯

I get the frustration, and no doubt I'll be pissed when I have a shot that's more affected, but amateur astrophotography seems like the least-important reason to be concerned about Starlink.

But then, the photo is going to get more attention, for sure.

Anecdotally, I took about 100 exposures of the comet last weekend with shutter speeds ranging from 10-20 seconds. There were satellite streaks in every exposure! I don't ever remember it being this bad.

It doesnt matter the impact of amateur astrophotography's work, starlink doesn't have the right to take that from them. I do think we need to evaluate whether these costs are worth it.

I go further.

I myself think we need to take a second look at city light. I'd like us to begin working on making the milky way visible again.

I agree. Vast populations of people can't know their place in the universe because they physically can not see it. What can we do to avoid that? In suburbs it seams feasible to stop building / start removing streetlamps in neighborhoods that don't necessarily need them, but I don't know how that would work in bigger cities

Better, more directional street lamps help, even in large cities. We can tune their wavelength to be less blinding as well. They do not need to illuminate the sky. More of them, and less powerful, would provide better light where it’s actually needed.

The other side is to reduce emissions of aerosols and particles that scatter light in the atmosphere.

> starlink doesn't have the right to take that from them. I do think we need to evaluate whether these costs are worth it.

Yes, but when doing that, let's also take into account the fact that Starlink exists to open up space access. Starlink doesn't exist (just) to provide Internet access, it exists primarily to fund Starship and further reduce costs of space missions. This makes it one of the most important thing happening for astronomy.

Yeah, so it basically exists to bring FB and Google to more people on the planet easier. We're selling out our skies to the ad industry. For free! What a great idea.

Textbook example for tragedy of the commons. Luckily we didn't do the same with earthly resources like water, air, wild animals, ... oh wait

... what’s the most important reason to be concerned?

Flipped on its head, I would say Starlink, or at least the underlying technology that makes it feasible (and it's all related, since it's all SpaceX) may be good for astronomy... eventually.

Space based telescopes give a much clearer picture than land based ones. You can't have ubiquitous and/or (relatively) cheap space based telescopes without a thriving launch industry that reduces costs. You can't have that without innovation and competition in the space launch industry. You are unlikely to innovation or competition in that industry the without a market need. Starlink is the market need right now.

Want lots of space telescopes to give you even better pictures? Don't kill off what's going to take you there before it begins. The astronomy industry needs to work with SpaceX to minimize the problem while also encouraging them (and anyone else working to drop costs to launch something into orbit) to succeed, not killing off or greatly delaying the oncoming age of ubiquitous and easy access to space telescopes because they are short sighted.

> Space based telescopes give a much clearer picture than land based ones.

Aren't those far more expensive to launch and operate?

Not necessarily? Starlink represents an order of magnitude improvement in both launch and hardware costs. And that’s with Falcon 9. Starship represents another order of magnitude improvement (or better, over time...).

Right now? Yes. As I understand it you get much more capability for your size of telescope if in space, because you don't have to look through the atmosphere. If launch costs go down (which they are), and satellite components and labor to build operate become cheaper (because of increased general experience, supply of parts and labor, etc), then space satellites become cheaper. If we get better at assembling things in space (which we're only going to do after demand and experience in doing it), it might even be easier to make a larger telescope in space than on land eventually, and the stresses of gravity on the structure for the mirror are greatly reduced or eliminated. It looks like all the recent large telescopes are with segmented mirrors now anyway.[1]

1: https://en.wikipedia.org/wiki/List_of_largest_optical_reflec...

It seems you're basing your assertion on projections based on wishful thinking. It's like saying to a cancer patient that he shouldn't worry about having cancer because in the future you believe there will be wonder drugs that fix everything. Well, perhaps there will be wonder drugs in the future, but what about real life, and real life solutions to real life problems? I already have a ton of money invested in earth telescopes. What good does it do me if you argue that in the future I might gain some capabilities if I scrap everything and buy a whole new infrastructure?

Moreover, you only need a guy with a wrench to fix a telescope on the ground. If your telescope is in orbit then the problem is a tad more expensive to fix.

> It's like saying to a cancer patient that he shouldn't worry about having cancer because in the future you believe there will be wonder drugs that fix everything.

Is the field of astronomy facing death because of Starlink? That seems a bit excessive.

I would say it's more like a national healthcare system covering only poor quality glasses for vision for a decade while they pump money into research and training for laser corrective surgery to both reduce the downsides and make it much more affordable, in preparation for covering laser reconstructive surgery at the end of that period.

> I already have a ton of money invested in earth telescopes. What good does it do me if you argue that in the future I might gain some capabilities if I scrap everything and buy a whole new infrastructure?

Again, telescopes aren't scrapping everything, astronomers aren't going to disappear. They're at most some percentage less useful than they thought they would be prior to this. That sucks, but homeowners have complained about other people moving in and obstructing their perfect view for a long time, so it's not entirely new. I don't support Starlink because I think SpaceX has some right over astronomers, but because I think humanity as a whole benefits from more industry in space, and there's a solution for astronomy on the other side of this, and I don't want humanity held back because astronomers feel it infringes on a domain with a problem they've generally not had to worry about (even if they would probably argue that they are doing it for the benefit of humanity by providing knowledge).

Bottom line, I think the benefit to humanity from increased space industry is greater than the benefit unhampered astronomy provides in a case where we impede that industry.

To be honest, I understand where you are coming from, and share your opinion that many issues are more important than astronomy, including humanitarian issues. I think actually most astronomers would agree with that (the ones that I know, anyway).

But the problem here is with the way that this debate is being framed. There is a false dichotomy that has been repeated here which I sum up as basically "Space-X is trying to solve humanitarian problem A, and astronomers are getting in the way! Deal with it astronomers, you are not more important than humanitarian issue A." but that's not at all what's actually happening. This is a monumentally impactful project undertaken by Space-X in secret, with enormous ramifications on science that -- despite the simplistic claims here -- are not something that can be worked around (LSST and other projects cannot be done in space, regardless of the cost of space delivery). Instead of responsibly investigating the impact, consulting with scientific agencies to either mitigate them, or prepare for the impact (as they are doing now after a huge outcry, but there is little that can be done now), they have instead opted to completely blindside entire branches of science, ruining decades of work around the globe and impacting tens or hundreds of billions of dollars in R&D. Even their press releases now say things like they are "learning how astronomical detectors work" -- that is extremely disturbing. That should basically never happen. There are responsible ways to do what Space-X has done, and they have shirked those responsibilities.

Yep. Lots of very clearly uninformed opinions here. Can confirm there are many advantages and disadvantages of space-based vs ground-based telescopes. Saying "well astronomers should just use space telescopes those are better" is quite ridiculous and reveals a deep ignorance for how astronomy is actually done (as though an entire field of science has not maybe had that thought?).

Extreme expense and complexity of space based telescopes is one large downside (saying "well space x will make that cheaper" um, maybe? but that will not happen for quite some time, and you realize you are parroting a PR department known for being hyperbolic? While ignoring the actual, real impact these satellites are currently having on billions of dollars of astronomy research, which happens on 10-20 year timescales?).

There are numerous benefits conferred by ground based telescopes that cannot be accomplished in space. Ground based telescopes allow you to have much larger collecting area, allow you the option to maintain + upgrade instrumentation (not possible in space, and if someone mentions "hey they replaced the hubble mirror, didn't they?" yes, at the cost of 250 million dollars), not to mention the barrier to entry for building ground based instruments is much lower and allows smaller projects to have a large impact without requiring a ridiculous amount of funding. See, e.g. https://www.astro.princeton.edu/~gbakos/satellites/ <- one astronomer's page detailing the impact these satellites currently have on his work; this is just one example. Lots of links, e.g. https://www.forbes.com/sites/startswithabang/2019/11/27/this... that will confirm the bare basics of what I'm saying here.

People thinking "oh well ML should fix that" may also be completely unaware that: no it cannot, unless you just want a pretty picture, because astrophysics is done on pixel-level brightnesses and once you saturate a pixel, there is no more information there, not to mention that even non-saturated pixels will have an insane amount of noise now, which degrades the SNR of otherwise good observations. Astronomy is done with some of the most sensitive optical/IR/radio equipment that exists (a large motivation to fund astronomy is for the innovation here that is relevant to other applications).

People saying "oh but space x is going to add some anti-reflectivity coating so it'll all be alright, Elon will fix it." Ohhh boy. Yikes. Here's the incredible page addressing this on space-x: https://www.spacex.com/updates/starlink-update-04-28-2020/ <- it's incredible because it flat out admits to an astounding level of ignorance about the impact of this, and makes several promises that may seem nice to a non-astronomer but basically amount to "we'll do something but it will not really change anything at all for any astronomy research, but we totally understand now that someone has finally educated us on the bare basics of operating in space."

> For example, earlier this year we launched DarkSat, which is an experimental satellite where we darkened the phased array and parabolic antennas designed to tackle on-station brightness. This reduced the brightness of the satellite by about 55%,

To give you an idea of how completely meaningless this is to astronomy: these satellites currently have an average magnitude of 5.5, brighter than the brightest stars, and virtually all of astronomy tries to be sensitive to > 10th mag (i.e. 1.5% of the brightness of 5.5 mag, so we're looking for > 99% brightness reduction before this even begins to mean anything) + this coating will affect IR measurements because black coatings are black because they absorb light, and things that absorb light get hot and things that are hot emit IR radiation. LSST will have a 5-sigma single exposure sensitivity of at least 22 mag (0.000025% of the current satellite brightness, no that is not a typo, so we would need 99.99997% brightness reduction).

> The huge collecting area of a larger telescopes like Vera C. Rubin Observatory leads to a sensitivity that will render even the darkest satellites visible.They are so sensitive that it won't be possible to build a satellite that will not produce streaks, in a typical long integration. There is much that can be done to reduce the impact of satellite streaks, and that starts with an understanding of how astronomical sensors work.

So nice of them to think of that, um, now? The rest of that section is a goldmine, saying basically "here is why we really can't mitigate this for CCD detectors used by all of astronomy because, well, they are looking at dim things and bright things ruin a large portion of the observations" while also concluding with

> While it will not be possible to create satellites that are invisible to the most advanced optical equipment on Earth, by reducing the brightness of the satellites, we can make the existing strategies for dealing with similar issues, such as frame-stacking, dramatically more effective.

No, no, no, no, no and no. There is absolutely nothing you can do with 30,000 5-6th mag satellites in the sky at all times. They will be in your images. Frame stacking will help to a point, but not even close to what you would need (not even within a few orders of magnitude). We will lose a large amount of effective sensitivity and a large amount of science will be completely lost.

People still shrugging this off should remember: instruments like LSST cost the taxpayer half a billion dollars and took 20 years of development, countless and priceless time investment from a large fraction of astrophysicists and astronomers (many at the top of their field), and would allow us to do incredibly impactful science, both from a philosophical standpoint (being able to observe 20 billion galaxies + stars allows you to do cosmology and other astrophysics that is otherwise impossible, see the science book: https://arxiv.org/abs/0912.0201), and from a practical standpoint (like NEO's)

So: even if you don't think astronomy is important, you should still care about this. It's a colossal waste of money due to the complete arrogance and ignorance of one rich guy. Absolutely did not have to be this way.

>makes several promises that may seem nice to a non-astronomer

Elon Musk's entire MO is appealing to non-experts to drive the narrative, whether he's talking about Full-Self-Driving cars, or underground car tunnels, or Hyperloops, or a brain implant curing dementia, or these satellites. It's scary.

Look at some of the replies in that Twitter thread, "He's literally bringing internet to under-served locations!" as if any of this project is even functioning today, or there is no other way to provide telecoms to these places.

Each starlink group is inserted at a low orbit, booted up and tested, and then they boost themselves to a higher orbit over a period of a month or so. During this boost, they orient their panels horizontally to minimize drag. Once they reach their final orbit, they rotate their panels vertically, at which point their visibility goes way down (mag 5 (prior to the new coating) down from a mag 0).

I've seen plenty of people saying some variation of "there are only 600 of these now, imagine what it will be like when there are 42k of them..." If I understand correctly, the number of bright satellites will be proportional to the launch rate, not the total quantity in orbit. Going off Wikipedia, they have launched about 1/8th of their 2024 goal, and the majority of the remaining satellites are destined for much higher (and dimmer) orbits.

https://en.wikipedia.org/wiki/Starlink#Constellation_design_...

>If I understand correctly, the number of bright satellites will be proportional to the launch rate, not the total quantity in orbit.

Because the constellation needs constant replenishment, the launch rate (and hence the # of brighter satellites) will have to reach a steady state that is directly proportional to the size of the constellation.

We can extrapolate that in the future this rate will actually be significantly higher than it is currently:

They currently have permission to launch around 12,000 sats. They're launching around 250 per year. The current launch rate is only sustainable if each satellite lasts for 50 years.

If you expand that to the proposed 42,000 constellation, 250 new satellites per year is only sustainable with a MTBF of around 150-200 years per satellite, which is nigh impossible in low Earth orbit. Using a lower (but still very generous and optimistic) MTBF of 10 years, Starlink will need to launch 4,200 satellites every year, about ~15x higher their current launch cadence.

> the majority of the remaining satellites are destined for much higher (and dimmer) orbit

Just about all of the satellites they've orbited so far are hanging out around 550km. SpaceX initially got permission to go as high as 1300km, but they've since changed their mind. The new plan (still pending FCC approval I believe) is to keep all of the satellites between 300-550km. So the future satellites will be as low or lower than the current ones.

It's bad faith, a normal stacking would have made them completely disappear, it's one of main reasons to do stacking, remove things which are not on all images, and it's works flawlessly.

You have to actively tweak your settings to create this kind of photo.

I guess the most basic way to stack (just add the images together) would leave them in, but

> Almost every modern astronomical post-processing program has a rejection process (sometimes referred to as sigma-reject) to remove unwanted signals, though the exact sequence will depend on which program you use.

https://skyandtelescope.org/astronomy-blogs/imaging-foundati...

From your link:

> The way this process works is that, while averaging all of the pixels in a series of, say, 10 images, the program mathematically calculates which pixels fall far away from the mean value because they're much brighter (or much fainter) compared to the same pixels in other frames. The algorithm then discards those out-of-range pixel values so they don’t affect the final image.

Wouldn't this process remove part of the comet trails as well as the satellite trails?

I mean, I get how it works if all you care about is relatively static like distant stars, but would it work for this specific use case?

No, because the comet does not perceptibly move in the sky during the acquisition. All comet pixels are present in every image.

The comet does not change but its position in the sky does btw. Longer exposure times turn points into streaks if the object is not tracked to compensate for this.

Yes, I assumed tracking as it's basically a mandatory requirement when you do telephoto astrophotography, and definitely used in the OP photo. The alternative is to shoot wider angle and align the images during stacking, but either way you have to get your subject's pixels aligned or the result is just blur.

This is true of every single object in the night sky, and is why an equatorial tracking mount is table stakes for good astrophotography.

The most common algorithm to manage airplanes, satellites, hot pixels, and other undesired photons in astrophotos is a process called Kappa-Sigma Clipping. It essentially rejects pixel values from subframes in your image stack that fall outside a user-inputted deviation from the mean.

In other words, the process works wonderfully to get rid of the starlink-emitted photons, but you lose that subframe's signal, lowering your signal to noise ratio. Not the end of the world. But inconvenient and sometimes costly to professional astronomers.

Yeah, but what % of subframes (small portions of large images) are ruined by noise caused by moving objects? Way less than 1% I'd imagine. It's just not a big problem. And certainly not worth outlawing new satellite launches over.

Take a look at this

https://photoshoptrainingchannel.com/remove-tourists-stack-m...

> You have to actively tweak your settings to create this kind of photo.

No, the most basic stacking is just to add the images together, resulting in trails. I don't see this as bad faith at all.

If it created trails, then it would also multiply the brightness of the stars and the comet by the number of pictures (17 in this case). Each satellite appears only on one photo, while the stars and comets appear on all 17 in the exact same spot. The only way to stack them to get a normal looking stars and comet is to make an average. And since the satellites only appear on 1 out of 17 they would effectively disappear.

Unless you actually want to have the satellites there, then the stacking would just cut the region with the satellite from each photo and simply glue them together. That's how you can get this image.

I actually just tried it in Hugin. Normal stacking from 2 pictures by default made the objects that appeared only on one of the pictures semi-transparent. If I did this with more pictures, they would be so transparent that I wouldn't see them at all. But I could manually select a mask to cut out the portions that I don't want. If I select and exclude the object (satellite streak) it would disappear completely. But I could also purposefully include the streak and in that case all the satellite streaks would be included in full brightness in the result. That's most likely how this photo was made.

Apart from all the comments about this being a bad faith post, I wonder about the utilitarian argument, if you take it at face value. If you could provide decent internet at low cost to large parts of the world that are underserved, at the cost of ruining ground-based telescopes, is that a good trade-off? What if it's just certain kind of telescopes, or certain classes of astronomers (as this seems to be)?

I think this is useful if we also consider that part of SpaceX's plan is to make launching satellites cheap (in fact, launching anything cheap). So while ground-based astronomy will suffer, space-based astronomy will get cheaper and easier.

Presumably to the point where people who want to can subscribe to a Hubble-like satellite service and get all the space photos their hearts desire.

Also, we made a similar trade-off a long time ago - most people live in heavily light-polluted cities, because we value having street lighting more than being able to see the stars.

Cost of launch is not really main reason why we don’t see more space based astronomy.

1. Space is a hostile place, and developing telescope that works there is much harder. 2. There are very real limits on size and weight of what can be put there right now, and rocket equation is ruthless. 3. Any type of maintenance or upgrades are basically impossible, compared to earth based. 4. Adaptive optics were such a huge breakthrough, that basically negated need for most of space based telescopes.

I would call cost of launch to space the main reason, just not the only significant one.

Reasons 2 and 3 are big part of why launches of expensive.

There's a feedback loop in space launches: they're expensive, therefore you launch less, so you need to add redundancies and spend more time ensuring the payload will work, which raises the development cost and increases mass, which makes launches less frequent and more expensive.

Conversely, reducing the cost of access to space means you can send more stuff that's less robust, which shortens development time and makes it less expensive, and of course makes technological progress faster.

Which translates to: suddenly space telescopes may be more affordable, and more of them will be launched.

Some ground-based observatories have been productively operated for nearly a _century_, with improvements in instrumentation providing leaps forward in sensitivity. That amortizes the cost of the observatory (mirror, site, etc.) across many years.

Even with cheaper launches it's much harder to get that benefit in space--servicing missions are much more expensive than driving up a mountain...

But now if we are forced to move all ground telescopes on space SpaceX will make profit so is a win-win for SpaceX and the public will have to pay to replace working satellites on the ground with expensive and smaller ones on space.

We should be fair and acknowledge all the downsides, and if you disagree I would ask to waste a bit of effort and explain why we should ignore this costs on the public(maybe the costs are worth it in the long run but we should not ignore them)

Space telescopes are vastly superior to ground ones. There is no competition, imo the decreasing cost of launching will enable incredible telescopes in the future.

If you have same size yes but the issue in space you can send only smaller telescopes, this ones are inferior on some dimensions versus the big ones we have on high mountains on deserts but sure a small telescope in space is better then a same size on the ground.

Let me know if somehow I am wrong and for example Hubble is superior to all telescopes on the ground at the time it was launched. The best thing is to have it all, giant telescope arrays on the ground, telescopes in orbit, on the moon, on the other side of the sun/

That's a bit like saying that forks are superior to knives. They're good at different things.

Ground-based telescopes have a number of very significant advantages over space-based telescopes. You can build much larger and heavier telescopes and instruments on the ground. If you want to observe faint objects, you need more photons. To capture more photons, you need a larger primary mirror.

Space-based telescopes used to give higher resolution, but adaptive optics undo much of that advantage. In fact, because the diffraction limit is dependent on the size of the primary mirror, ground-based telescopes can achieve better resolution than space-based telescopes.

You can attach large, heavy instruments, such as massively multiplexed spectrometers, to ground-based telescopes. And you can switch instruments out and do periodic upgrades and maintenance.

Space-based telescopes have advantages in certain specific areas. They can observe wavelengths that Earth's atmosphere absorbs or emits at (such as the ultraviolet and infrared). They can achieve much better calibration, because there's no atmosphere to calibrate out. They can achieve high resolution across a wide field of view (adaptive optics negates the effects of the atmosphere in a small field of view). Sometimes you need these particular advantages, so space telescopes are critical. Often you don't, and ground-based telescopes are superior.

disclaimer: I know almost nothing about telescopes.

Isn't there a way of multiplexing lots of small telescopes together to gather more photons and effectively emulate a larger telescope in software?

If so, could you launch 1000 small telescopes into space and effectively have a (set of <1000) larger telescope(s)?

Multiple mirror telescopes are a thing. They can be used to gather more light or increase the angular resolution.

See European Southern Observatory's very large telescope.

AFAIK you can do that with radiotelescopes, but cannot easily with optical telescopes. That is because optical sensors lose phase information of incoming signal.

There are telescopes formed from arrangement of smaller telescopes (like mentioned Very Large Telescope of European Southern Observatory), but these have to be connected optically (by a system of precise mirrors), not just digitally.

That's correct. For optical telescopes, you have to physically combine the signals in real time to do interferometry. The VLT can do optical interferometry, and can create baselines as long as 200 meters (reaching nearly 100x the resolution that the Hubble Space Telescope achieves).[1] If you just combine the images from different telescopes, without doing interferometry, you only get one of the benefits of a larger telescope (you can see fainter objects), but you don't get all the benefits (e.g., higher resolution).

Interferometry is much easier with radio telescopes. You can record the waveform at each dish, and then digitally combine the signals afterwards (there is specialized "correlator" hardware that is purpose-built to do this very efficiently).[2] That means you can put receivers anywhere (on Earth or even in space), as long as you are able to synchronize the timestamps in the data well enough to digitally combine the signals afterwards. One of the major technical challenges faced by the Event Horizon Telescope, which imaged the black hole at the center of M87,[3] was synchronizing clocks at stations on opposite sides of the Earth. They had to physically bring atomic clocks from one location to another. After they took their observations, they flew hard drives with the recorded signals to a centralized location to do the correlation.

1. https://www.eso.org/public/teles-instr/technology/interferom...

2. https://www.aanda.org/articles/aa/full/2007/05/aa4519-05/aa4...

3. https://eventhorizontelescope.org/press-release-april-10-201...

Interesting, thanks :)

The article on interferometry implied that this is "just" a matter of computational difficulty - the higher frequency means that more accuracy and computing power is needed to resolve an image. Is that right?

If so, surely this is a Moore's Law problem, solved by waiting a few years for the needed computing power to be cheap enough to use?

By higher frequency, do you mean optical frequencies? If that's what you mean, then it's not just a matter of computing power. It's a matter of optical detectors not actually measuring the phase of the incoming photons. If you lose the phase information, you lose the ability to do interferometry.

CCDs just count photons (incoming photons kick electrons into the conduction band, and you count electrons after each exposure). There are more advanced detectors that tell you the energy of the photons, but not their phase. If you can't measure the phase of individual photons, you can combine light from different telescopes directly, and let nature do the correlation for you. That's what optical interferometers do.

Shouldn't 2( or more) smaller telescopes 1 positioned on the North pole and 1 on the South both on polar orbits pointing at the same spot solve that issue?

To me it seems like the moment we got a proper space telescope( Hubble) there was a ton of low-hanging fruit to discover at such a degree that so many years later we are still finding out new stuff. Compared to that Earth based telescopes seem to have to go through massive efforts to make headline discoveries( not that any other less discussed paper isn't important, it's just that... how would we know about e.g. the acceleration of the universe from an Earth based observatory?).

> Compared to that Earth based telescopes seem to have to go through massive efforts to make headline discoveries

That's a function of how the media works. Ground-based telescopes are extremely important for astronomy, and I would even venture to say are involved in most major discoveries. Space telescopes are also extremely useful, but they're also much flashier than ground-based telescopes.

> how would we know about e.g. the acceleration of the universe from an Earth based observatory?

By observing type-Ia supernovae (SNe Ia), for example. Not only is it possible to do this with ground-based telescopes, but ground-based telescopes are the primary way it is done. Most of the SNe Ia observations that went into the discovery of the acceleration of cosmic expansion were done from the ground.

It’s funny how many people who know nothing about telescopes have been saying that recently...

SpaceX going going to sign on the dotted line to provide free service to observatories damaged by starlinked? Because unless it signs a contract, this whole argument is a load of hot air.

This exactly. Satellites are incredibly useful and enable trillions of dollars of worldwide economic output that would not be possible otherwise. This is a very meaningful improvement in everyone's lives. We should not stop using them simply because they are visible in the night sky, and make astrophotography a little bit harder (though not much harder -- removing satellite streaks is a default enabled option in astrophotography image stacking software).

Its notntrillions, and should be done ina way that does not ruin other people's jobs

I don't think you realize how much economic productivity is enabled by telecommunications satellites, GPS, earth-watching satellites, and more. Even just having a better grasp on the weather is worth many, many billions of dollars annually worldwide. Let alone GPS and knowing where you actually are (and how valuable that is to practically any business that operates in the real world; we're even talking things as far-flung as automated tractors in agriculture that are enabled by GPS).

Phased array ground stations cost about $10,000-$100,000.

That's a lot of money. Considering that the company has reversed course on almost every promise it has ever made about Starlink -- orbit altitude, inter-sat networking, service area, cost -- I think it's a good bet that Starlink will ultimately just look like a capital-intensive Iridium-like network without the ability to service mobile stations. I imagine the US military will end up being the main customer.

> Considering that the company has reversed course on almost every promise it has ever made about Starlink -- orbit altitude, inter-sat networking, service area, cost

All of these things are coming, in subsequent revisions of hardware.

Everyone on HN should recognise the pattern - it's very much a launch of a minimum viable product.

If you're willing to take SpaceX at their word you are off by two orders of magnitude. I don't see why you wouldn't be.

Which is an order of magnitude less than a cell tower.

Presumably that phased array ground station will be attached to a cell tower, it's not like people are gonna connect their phones with Ethernet.

Still a good comparison to see the relative costs of the components involved.

The premise is false. Musk doesn't need to ruin ground based telescopes in order to make Starlink a reality. This issue could be resolved by going slower, Musk just doesn't want to wait.

Musk drives his team for speed because every one of his companies still has the "how much runway do we have" mindset. Lots of people can throw stones from their glass towers knowing they work at a company that will exist in 2030 or 2040, but SpaceX can't say that unless they are always moving.

The truth is most people will never notice the Starlink satellites. Because light pollution obscures the night sky so much you can only see the brightest of stars and nearly nothing close to the horizon. How many kids are hearing about this comet in the sky, rush out at sunset, and are then disappointed to only see the haze of city lights?

Truth is, most people never look at the night sky, period. But this isn't about most people; this is specifically about people who look at the sky a lot -- and those people typically seek out darker skies anyway.

> Truth is, most people never look at the night sky, period.

Truth is people never look at the sky period. Ask people when the moon is visible and most will say "during the night." But about half of the time, the moon is actually visible during the day. Wouldn't people realize this if they simply looked up?

That's because what they mean is that the moon appears more brightly at night, and I suspect you know this. You don't _actually_ think these people have never seen the moon during the day, surely?

> That's because what they mean is that the moon appears more brightly at night, and I suspect you know this.

No, I don't think that's the reason. The moon is frequently very bright during the day, not even remotely hard to see. Moreover, people are mostly outside during the day, meaning that most of the time they have the opportunity to see the moon will be during the day.

I think the reason is that a supposed sun/moon - day/night dichotomy is perpetuated by culture (for instance, clock dials that use an image of the moon to symbolize the night) and that culture has a stronger impact on people's perception of the moon than their personal observations of the sky. I think they have seen the moon during the day, but the moon is very rarely the object of their attention. They see it, but rarely do they notice it.

The reason for such a culture emerging seems obvious to me; the Sun's presence in the sky obviously correlates with daylight perfectly, making the sun an obvious symbol to associate with the day. But then what symbol would you use for the night? There's a clear day/night dichotomy, creating a demand for a symbol that's inverse of the sun. However there's no object in the sky that correlates so perfectly with the night. The moon isn't there half the time, but neither is any particular star. You could use generic stars, and sometimes that's done, but stars aren't necessarily visually distinctive. The moon is visually distinctive and so it's pressed into the roll of being the symbolic opposite of the Sun, even though a trivial glance into the sky reveals that it isn't actually opposite of the sun.

“And God made two great lights; the greater light to rule the day, and the lesser light to rule the night.”

I got into an argument with a second grade teacher (when I was in second grade) who insisted that the Moon was only visible at night. It still rankles me to this day how wrong she was, and how she could have easily been disproven simply by going outside and looking. Even worse, I think she was the science teacher or something.

I got into trouble with my fourth grade teacher over this. Sent to the principal's office even. Fortunately, the moon was new that day and I was able to take the principal outside and point at it.

Truth is I've seen the moon during the day, and if you asked me "when is the moon visible", I'd say "during the night" and if you said "ah ha trick question!", I'd say "unless cloudy", or "not the entire night" or "also at dusk" or "depends where you are" or other "guess the uncommon answer I'm thinking of". If anything your conclusion should be that I'm an idiot, not that I "never look at the sky period". But more reasonably your conclusion should be that people look at hoofprints and see horses not zebras - it's like asking "on what day of the year do you get older?" and getting the reply "on your birthday". It doesn't mean people think they don't age on other days or don't look at the clock, period, it means people think you're trying to hint that it's your birthday, or that you're blanking on the word "birthday" (or not a native speaker and don't know it), rather than expecting you stopped them for a science grilling.

You're going to say it's not a trick question; but it is a short question and expects a short answer "it's visible when X", and there isn't one, except the common approximation "Day: sun, Night: moon". Apart from that it's just a list of things which might be in the way of seeing it, and there's lots of them: "When it's above the horizon, enough not to be blocked by trees or hills, and the sky is clear, and the sun isn't too bright, and you're outside, and it's not behind a tall building, and your eyes are open, and you're facing the right way, and you aren't blind, and..."?

I find it astounding that just any old for profit company can decide to ruin a world-wide public resource just to turn a few bucks. In 2020.

I'd expect that from something like the East India Company in the 1700's or something. Not a modern company in a modern society.

Do you shake your fist at every airplane that flies overhead too?

The country agreed to that. One day the country may decide against it. No-Fly Zones can be created.

A US company airplane passing over my house doesn't impact people in India, for example.

Airplanes have proven utility. Airplanes proved their utility before bothering people worldwide.

The country agreed to the starlink satellites as well, considering they received FCC approval.

The country can still decide against it and now allow any more launches, and the satellites that are up there will come down naturally in a few years time. You may even be able to forcibly deorbit them if they still have propellant left (not sure if they do or not).

No-fly zones are almost always created for the government to do government things, and not for the direct benefit of the public (ie reducing airport noise for nearby residents).

A US plane passing over your house doesn't impact people in India either negatively or positively(except for the consequences of global warming). These satellites passing over the US and India can equally benefit people in the US and India. It's not like starlink is a US only service and SpaceX is going to prevent anyone in India from having access.

Satellites also have proven utility, as does the internet, which is why groups like the UN General Assembly HRC declared access to the internet as a basic human right.

What is not proven is if Starlink will work the way it's been sold to you as an idea. What is also no proven is if it can be profitable even if it does work. People in these remote places of the world are unlikely to be able to afford internet... not have a need or desire for it. They have other priorities.

Not to mention there's already ways to get very high-speed internet to remote villages that want it. The only barrier is cost - but for motivated villages and/or governments, it's not very expensive ($10's of thousands up front cost, trivial long-term costs). I've sat in many conferences with people building out wireless networks in remote regions - very fascinating work.

There's some pretty non-trivial chance Starlink was only approved because of the Cult of Elon.

SpaceX wants to put 1,584 satellites in orbit[1] to the cost of around $10 Billion USD, and will need to replace these routinely due to orbital decay.

There's only 2,666 satellites in orbit currently[2]. 1,327 of which are from the US[2].

Re: No fly zones - they can be established for all sorts of things. There's no fly zones around many amusement parks, for example, and not just because of the remote possibility of some terrorist attack.

> UN General Assembly HRC declared access to the internet as a basic human right

That seems simply to be virtue signaling. Of course everyone should have access to information and knowledge, but that's not exclusive to the internet.

It costs money to provide internet access. Basic Human Rights don't cost money to exercise. The Right to be Free doesn't require a monthly payment to some mega-corp. If it did, you would not be free, would you?

[1] https://en.wikipedia.org/wiki/Starlink

[2] https://www.ucsusa.org/resources/satellite-database#:~:text=....

Literally anything that hasn't been done yet hasn't been proven, so I don't really understand how you can use that as an argument against it. At worst, if it is unsuccessful, then the satellites will just stop getting launched and will all fall back to earth after a few years, and Elon et al will be out a few billion dollars.

> People in these remote places of the world are unlikely to be able to afford internet... not have a need or desire for it. They have other priorities.

Not my experience visiting some remote areas of India, Nepal, and Tibet. A single anecdote, but I gave a man a ride to the top of a mountain near Ganden monastery so he could use his cell phone. He went with a list of messages of various people in his family and who to send the messages to. He would normally walk 3 hours uphill in order to get service to send those messages (This was in 2007, maybe things have changed since then).

> The only barrier is cost - but for motivated villages and/or governments, it's not very expensive ($10's of thousands up front cost, trivial long-term costs).

Many places in the world wouldn't be able to drum up tens of thousands of dollars, and it isn't for a lack of motivation. But they might be able to drum up $500 and then $60/mo.

> There's some pretty non-trivial chance Starlink was only approved because of the Cult of Elon.

The FCC isn't composed of the twitter mob or the spacex subreddit.

I'm not really interested in debating positive or negative rights, or whether the UN was virtue signaling. My point was that many people view internet access as extremely important for humanity, and starlink and other projects may be an incredible boon for the world, at the expense of some astronomy observations.

“This was in 2007, maybe things have changed since then).“

So before 3G, when AT&T had an exclusive deal to sell a locked iPhone.

I mean I remember having to use dial up for the first time in years when I lived in Spain in 2005!

Well, if Starlink isn't profitable, it won't be long until all those sats have deorbited, either.

> It's not like starlink is a US only service and SpaceX is going to prevent anyone in India from having access.

I'm not sure this is entirely true. SpaceX is US corporation. They could easily decide to deny access, or otherwise limit what people can do, based on policies set by the US government.

See also, the GP post, referencing the East India Company.

EDIT: The point here is not whether StarLink is a net benefit or not. It's that it's a predatory capture of resources, fuelled by capital and advantages, which won't be passed down, but have a good chance of being used for further leverage.

EDIT2: I'm not against advancement, far from it, but if there are no tools to manage it, then we end up with oil companies again.

They could easily deny access, but there is no compelling reason for them to unless forced to by the government. Other countries denying starlink access to their own citizens is a much more likely outcome.

I don't understand how starlink is a predatory capture of resources. It's not like they are saturating LEO and no other satellites are allowed to be launched. There are multiple companies planning high speed satellite based internet, including one backed by the richest person in the world.

And by virtue of being one or two of the richest people in the world, they have the right to do what they want in the atmosphere, pay no-one for it, and profit.

I think Jesse Pinkman said it best, "dolla dolla bills yo"

EDIT: It's not whether the technology is useful or not, it's about whether you are be ok with a handful people using natural resources in the pursuit of more wealth and influence, with no regard for the consequences. If you can't see any parallels in history, then :shrug:

No, not by virtue of them being some of the richest people in the world. A million people could all pitch in $5,000 and form a satellite internet company if they wanted, and it would play by the same exact rules that spacex/bezos/whoever is currently out there.

Who would you suggest gets paid for putting satellites up? Who does American Airlines, or the random dude in the Cessna pay in order to fly over my house?

And yes, they can profit, just like telecom and other companies that use satellites do.

> with no regard for the consequences

The consequences being globally available internet, at the cost of a couple hundred scientists having a harder time doing the observation. If you can't see the upside because of the downside, then :shrug:

I think the issue some want to call attention to is not the consequences that have occurred so far, it's the process of disregarding consequences.

It's like how people have been upset recently about secret police; it can't be reduced to the specific actions that we know about, it's the process being unacceptable to some.

Not me, but I know I read something once lamenting that almost any place in the world, you can be lost in the wilderness but will still see the occasional plane or at least contrail, and thus can't avoid civilization.

This is how many externalities work, most just aren't so globally distributed.

im 100% against that commercial project is destroying my night sky.. its like building highway through my yard.. our already overglobalized world will be even more 'globalized' in the hands of few.. w t f..

What are some of the potential consequences of this? I’m curious if stars getting photobombed is a signal pointing to a greater issue? If they can coat them in a way to not be reflective then will most astronomers be satisfied?

The greater thread has some data on the latter point - the latest satellites are coated, but it's not had much impact yet.

Seems like this is light pollution taken to a completely new level.

I remember reading Musk had to get permission from some US regulator (the FCC and/or FAA maybe?) in order to launch these satellites but is there any sort of international body that deals with this?

To a first approximation it's just the FCC, but the FCC does listen to and evaluate issues pertaining to light pollution, space debris, satellites falling to earth and landing on peoples heads, and so on despite that not being related to radios.

SpaceX has abandoned the coating approach and is going with a shade approach, which works even better. The next set of satellites all have the shade.

We will exchange white lines for black lines. We won't be able to see through the satellites.

Actually maybe a white line is simpler to remove than a black one on a black background.

exactly, paint them green

Presumably exchanging white lines for transparent lines not a color. For larger projects which don't move around this can be augmented further by removing known satellite tracks instead of lines, or even not imaging areas when satellites are going to be there.

Black lines are far preferable because they do not contribute to the total amount of light collected. A momentary flash from a bright light can swamp the sensor, but a brief moment of blackness will leave the pixels' state much less disturbed.

This is why long exposure photographs of roads have light trails with no cars.

Any good astronomy imaging tool will remove temporary satellite flashes without much effort, provided you take a lot of exposures. If you naively stack them you get this of course.

> If they can coat them in a way to not be reflective

Less reflective. I don't think there's a way to make them not reflective, and many, many astronomical objects are very dim.

> > If they can coat them in a way to not be reflective

> Less reflective. I don't think there's a way to make them not reflective, and many, many astronomical objects are very dim.

Vantablack[0] would probably be adequate for the timescales involved, at least for most terrestrial[1] observations:

[0] https://www.sciencealert.com/this-object-has-been-sprayed-wi...

[1] eg. I can easily imagine a similar but more severe problem for a lunar farside observatory if (when?) Starlink is expanded to provide internet coverage for the Moon's surface. Of course, the main reason for a farside observatory would be shielding from Earth's RF emissions, so just people needing and wanting internet access on farside is probably going to be a problem first.

Wait till we have the first moon bases and there will never be a new moon again.

Can't wait!

I wonder if these things will have any effect on astronavigation. It would be sad to see such a cool practice become impossible.

Starlink Satellites are only visible for short periods just after sunset and before sunrise, because most of the night they are in the earths shadow.

Yeah. That's the problem. Celestial navigation can only be performed during twilight, as you need to be able to see both the horizon and celestial objects.

https://en.wikipedia.org/wiki/Twilight#Nautical_dawn_and_dus...

I can't imagine it would; Starlink satellites are also moving. Quite fast. So don't do your celestial navigation by the moving thing and you'll be fine.

I don't see why they would. The stars typically used for astronavigation are very bright; brighter than starlink satellites. A brief web search leads me to believe typical starlink satellites have a magnitude of around 5 or more, while the stars typically used for astronavigation have magnitudes of less than three (https://en.wikipedia.org/wiki/List_of_stars_for_navigation)

Even if that weren't the case, it's easy for the human eye to distinguish a star from a LEO satellite; the satellite is the one that's moving fast. I see no reason the sailors couldn't simply ignore the satellites.

It was the brightness I was worried about, yes. Should've probably just looked it up myself!

I don't think astronavigation is used in any serious capacity anymore, so in that sense it's a moot point. Still, it's a cool practice and it would've been too bad to see that go away.

There's a tension here, and I'm not saying that I know where the appropriate balance is-- but it's a tension between the positive societal impact that inexpensive and ubiquitous broadband may have, vs. the societal impact of scientific knowledge from ground-based observatories.

I'm sure there's other ways of solving the broadband problem. I'm sure there are other ways of getting the astronomical data. I'm also pretty sure that all of them would have their own trade offs. Everything does.

In this case, I think the unilateral approach that Musk is taking has hurt perception of the project as much as the trade offs represented by the project itself.

Perhaps to remedy the situation, SpaceX would do well to introduce a large fleet of freely-accessible amateur astronomy platforms with some kind of timeshare credit component? I ordered several images through a university terrestrial telescope as part of an astronomy course and it was a great experience to refine the object's orbital parameters based on the observations.

This is pretty much a cherry picked worst case scenario. The comet is only visible right above the horizon after sunset for a brief period.

Starlink satellites are also only visible low on the horizon, and only for brief periods after sunset and before sunrise, because their low orbits keep them in the Earths shadow the rest of the night.

Yeah its basically optimized to look bad. The satellites are relatively close to each other. In normal operation, there's no reason to have 30 different satellites in view. I suspect these satellites were very recently launched, so they are not in the normal sun-tracking orientation.

Also, the comet is a wide object. A wide image is just more likely to have any satellite in view.

That’s odd, I took a bunch of pictures of that same comet and saw no satellites at all. Did I do something wrong?

That looks so cool.

The OP posted this in the ensuing Twitter argument...

> Why (on Earth) do you want to become a multi planetary species??

That's just an un-neccesarily foolish question. Why does a dog swim when you place him in a lake?

> Have you ever tried to live in Antarctica or in the Atacama desert (I have)? I support science, exploration, tech development but not foolishness. Do you surround your house with roads to explore distant locations?

Isn't that exactly what we've done as a society already?

We did that, realized it was a mistake, and have started placing emphasis on working around nature, instead of tearing it down because it's more convenient.

in the west, yes. In the places where real nature still exists; no, everyone's still happy to tear it down for convenience.

evidence: Brazil's rainforest. Indonesian palm oil. Chinese mines. African, well, everything.

I sometimes think the West overestimates how convenient or cohabitable nature is, because they were born into a tamed version of it.

For most of human history, nature has been trying to kill us (if that's too anthropomorphic, we can go with the longer-form "The processes of nature are ambivalent to the survival of our species and individuals in that species, and there is no guarantee that the natural world is one habitable by humanity. Our species' history is shot through with plagues, floods, famines, and predation, and much of our technology was created to minimize that.")

> The OP posted this in the ensuing Twitter argument...

"OP" refers to the OP of the Twitter thread.

I'm just the submitter and do not share their view on being a multi-planetary species at all (I agree that it sucks to have streaks on your astro-photos, as I started taking them recently).

We have to boldly go where no man has gone before.

Edit: changed wording to restore split infinitive.

or even go boldly

Thanks, fixed.

> That's just an un-neccesarily foolish question.

On Twitter there seem to be a lot of people on who expect to live in other worlds soon, and not just to explore and study them. He's likely rhetorically responding to that idea. And I think it's worthwhile to confront those ideas critically. IMO as well, living off of Earth sounds hellish, given what we know now.

The person the Twitter poster is talking with is now suggesting that many people will abandon their physical bodies, and those that won't will live in cylindrical space colonies. He's speaking fantasies.

Twitter OP is also arguing that there will never be human settlements off this Earth, which is bullshit.

Assuming humanity exists long enough, it will expand throughout the solar system. At very least to the moon.

We can argue about how long that might take, but not about it ever happening.

>Assuming humanity exists long enough

That's a big assumption.

There's also the why question. What's on the moon that would make it worth all the difficulty to get there? I suppose we might have a semi-permanent research station on the moon or even Mars, but colonization? Unless we make some really unlikely discovery like unobtanium is only found on Europa and it's really super useful, we're not going to have space colonies.

The moon will be a good source of water for spacefaring endeavors of the future, due to the large quantities of ice it has at the poles. With 1/6 the gravity of earth and the appropriate infrastructure in place, it will likely be cheaper to get that water off of the surface of the moon than from the Earth. The most promising use here is actually for producing methane fuel from this water. An industrial base of sorts could develop around this.

The other potential industry will be moon tourism. It could become something like the new Mt Everest. Obviously only for the very rich at first.

Once it becomes a real possibility and not some crazy sci-fi project, governments may start competing, so as to not get “left behind”, even if it is not immediately profitable.

One way or another, unless we destroy ourselves, it will happen eventually. There’s a percentage of people who are just absurdly curious and adventurous, and want to go where no one has gone before, even if the cost is immense. Hell, for some, I’m sure even just desire to get away from their situation on Earth will be a big part of why they go for it. People like this will build the first settlements and bases on the moon and elsewhere in the solar system.

Edit: sorry for the constant edits. It’s a bad habit — I don’t always get my thoughts out on the first try.

So, going to space to the moon is useful because it enables going further out to space.

And I'm not entirely sure how you turn water (H₂O) into Methane (CH₄). Granted I barely passed freshman chemistry 33 years ago so my chemistry knowledge isn't so good, but as near as I can recall, there is no process that will turn that input into that output.

And again, even if the moon is a source of water, there's not a significant need for any water mining operation at the poles to have a colony around it or even any human staffing. Putting people there on even a semi-permanent basis would likely eliminate any gains to be had from using the moon as a source of water.

Even the space tourism doesn't call for settling the moon. No one lives on top of Mount Everest either.

Could you simply separate hydrogen from the water, using electrolysis, or other methods and then use the Sabatier reaction? [1] Carbon dioxide in bulk may be harder to come by on the moon, however.

Also, the Lunar Gateway [2] is a key part of the plans by NASA/SLS. It's not about settling on the moon, it's about making it a stop off point to refuel or pickup supplies before going on to a further off destination like Mars. Instead of having to have all your fuel and payload when taking off from Earth, you can have a lot of your supplies and weight on the Moon. This means your trip off Earth can be cheaper. Getting out of Earths gravity and getting to escape velocity is the hard part. Getting off the moon is a lot easier.

[1] https://en.wikipedia.org/wiki/Sabatier_reaction [2] https://en.wikipedia.org/wiki/Lunar_Gateway

The Sabatier reaction relies on carbon dioxide. For the concept of using it to generate rocket fuel, there's a reliance on atmospheric CO₂ which is viable on Mars but not the Moon (which is why the section in the Wikipedia article is called “Manufacturing propellant on Mars”). And the Lunar Gateway is irrelevant to what I'm arguing, which is that there's not really any reason to settle off-planet.

> On Twitter there seem to be a lot of people on who expect to live in other worlds soon

On Twitter there seem to be a lot of people who currently live on other worlds.

For a different type of analogy, look at how long we had to sail around in wooden ships before that evolved.

Without actually venturing out there, we might never develop viable star travel.

I found that a bit of an odd question, besides the point, but I might be missing something. Is any of the purposes or uses of Starlink actually related to something multi-planetary? From what I read on it they seem to be there solely for communication on earth itself? Or does the commenter consider Starlink as one of the things further enabling technology to go multi-planetary? Which I still don't really get, since other types of communication are already which go way deeper in space and send messages back and forth to earth.

A major (the major?) motivation behind Starlink is to try to earn SpaceX vast amounts of money that Musk can invest in settling Mars.

See, e.g., this link for comments by Musk: https://www.space.com/spacex-starlink-internet-satellites-ma...

I wish we would discipline ourselves to avoid ruining that one planet before we get delusions of grandeur and the urge to wreck another one.

All these talks about “multi-planetary species” are bunk in the long term, anyway. We will probably have observation outposts scattered across the solar system, but that’ll be about it for quite a long time. The only realistically reachable planet in the foreseeable future is Mars. We could fix our issues with Earth for a fraction of what it would take to make it inhabitable.

We’ll send our billionaire pioneers to the moon alright. With a scientific base as a side effect. It still won’t improve anything that’s wrong with Homo Sapiens.

i can't believe people are suggesting to edit this away with photoshop... you are pointing at the moon and they are looking at the finger...

It was caused by stacking incorrectly in photoshop to begin with.

That the image tweeted is a product of photoshop in the first place should be obvious to anybody who looks up. Go outside tonight and look up. Does the sky appear as it does in that tweet? Obviously not.

It's the result of some image processing. For example, there are like a hundred segments in the photo, but if you look carefully, they are quite aligned in ~27 almost parallel lines (probably the 27 satellites in different frames?)and a strange almost parallel segment (probably another unrelated satellite?).

And how about that black hole photo from last year? Definitely a hoax--black holes are supposed to be black, dummies!

The image being the product of a computer program processing data does not mean that it's a hoax. That's moronic, and it's not even remotely what I'm talking about.

Fixing the image is not a matter of "editing it out in photoshop". It's a matter of processing the data correctly in the first place, e.g. not editing it in. The author of the tweet stacked his images to show every satellite instead of removing every satellite, which is ass-backwards.

Easily solved in software by removing the small part of each frame that has a satellite in it. Satellite tracks are completely predictable. This is not novel.

Perhaps true for amateur astrophotography but not the case for professional astronomy. Please see reporting in e.g. [1] and [2].

Note that simply putting telescopes in space is not a viable solution to these problems.

[1] https://skyandtelescope.org/astronomy-news/starlink-astronom... [2] https://www.theverge.com/2020/3/24/21190273/spacex-starlink-...

A few particularly large and particularly sensitive telescopes will have problems not easily resolvable by software, the vast majority of telescopes will not.

That actually sounds worse. Large expensive telescopes will have issues, but amateur astronomers will say there isn't any issue because the pictures they take with their smaller telescopes are cleaned up with software.

Arguably so (I'm going to generally stay out of value judgments), but do note that it's not all large expensive telescopes, it depends on the telescope.

... which has always been true.

Several observatories were built near cities. As light pollution from terrestrial sources have increased, they've found their expensive optical telescopes become toys, and have moved their scientific collection utility over to radio.

Yes, these are massively important to professional astronomy and our understanding of the universe.

Such concerns should probably be balanced against the potential the launch capacity of Starlink represents.

I'm looking forward to someone launching a satellite telescope network with the collection radius of an Earth orbit.

Somehow I get the feeling people who do this professionally understand what's possible and what effect this has better than you.

They undoubtedly do, but this is an opinion formed by talking to people in person in the industry. Random twitter users who manage to get there tweet on HN is not even close to an unbiased sample of professionals in the industry. My sample undoubtedly also has its biases, but is not selected for sensationalist views at least.

This is "I talked to some people" vs the linked tweet from a person in the industry. I think you can understand my skepticism. I also understand you probably don't have a convenient way to prove your side of it.

The person who posted this tweet? I don't think so. They also said this gibberish:

>Space junk. There HAS to be another way to improve internet communications, does Humanity and planet Earth's livestock need this (5G)? Really?

Sometimes people with real domain experience on one topic try to have opinions on other things. It doesn't always go well.

Yet another physical layer problem conveniently solved by a software solution (coded over the weekend, of course)!

Did have a thought about a physical device/notification system that lets you know the sky is clear, would be interesting to work on that the tracking/predicting position assuming data is available.

How did we get to this cargo cult where sitting on our behinds taking photos of the stars and un-ironically posting on the internet supersedes mastering space.

It's mostly the media, who care's not for science at all pushing this 'we should be outraged', but we eat it up.

Starlink and others helping the world will also create a whole new genre for ground based space photography the super rich can get into, but this drama is so tiring.

If you want humans to become a space faring people, you need to accept the idea that there will be at least 1000x more things in space.

People's comments here are generally insane to me.

Let's go to other planets. Let's build a Dyson swarms of O'Neil cylinders with a quadrillion humans living in luxury. Let's keep the light of consciousness alive.

Some things will change along the way, like amateur photography.

How much sympathy can I really spare for a purely leisurely hobby like backyard astronomy vs. satellites, Starlink, and our space tech?

To me it's like complaining that your photography hobby is harder now that more people can afford to travel and they get in the way of your favorite tourist shots.

I'm sure there are good examples of trade-offs that matter here like the impact on terrestrial research telescopes, but a guy snapping a pic of a comet and ranting about it on Twitter frankly has the opposite effect on me.

True, because professional astronomers, lucky them, are provided a completely different sky devoid of satellites, debris and other man-made objects.

If we can make space travel cheap enough to get more Hubble-like telescopes up there, then yes, this.

I believe that's part of the goal of SpaceX

Yes, but the point is that we should do that first before polluting the night sky.

There are also reasons for humans and animals to not want new, moving stars for reasons other than pure utility. At the very least, these shiny beacons are an insulting advertisement for Musk.

Next, people will be defending a Pepsi ad on the moon or something. https://www.theatlantic.com/science/archive/2019/04/pepsi-ad...

I am sure we will not have the space tech soon that can build giant telescopes in space, Hubble is small compared with the larger telescopes on the ground, and from what we can see today it takes decades to send a new telescope in space because you can't go and tweak it. I just hope the benefits are larger then the costs and we the public will not have to pay SpaceX to send telescopes in space to fix the issue SpaceX created.

Hubble costs are estimated around $10 billion USD in 2010[1].

The cost to put the thing into orbit is minuscule compared to the equipment and operation itself.

Put another way - SpaceX isn't solving any problems here.

[1] https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Challen...

it is a tragedy. what we have in the ever shrinking dark night sky is utterly breathtaking if you have ever seen it; light pollution is a bigger problem imo than starlink, but they relate. survey astronomers and astrophysicists and you will find for many it was being able to look up and see stars, be awed by them and wonder about them that got them into their field in the first place. i am scared to lose that..

> How much sympathy can I really spare for a purely leisurely hobby like backyard astronomy vs. satellites, Starlink, and our space tech?

Your sympathy or lack thereof is your business, but astronomy is one of the rare sciences where amateurs still do a great deal of work and make important discoveries.

> I'm sure there are good examples of trade-offs that matter here like the impact on terrestrial research telescopes, but a guy snapping a pic of a comet and ranting about it on Twitter frankly has the opposite effect on me.

It's a shame you would allow your opinion on an important subject to be swayed by a single tweet on an issue you apparently know little or nothing about.

How about when satellite stray signals or signatures start to pollute not just amateur hobbies, but GPS, weather? It's all related.

Satellites have very constrained transceivers. This is not only for regulatory reasons but efficiency. It's a literal waste of power to leak noise into non-target bands. Everything from the transceiver electronics to antennas are tuned for target bands. Satellites broadcasting stray signals is rare enough to not be a thing.

Interference with GPS and other signals overwhelmingly comes from ground based sources.

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