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Comment by prpl | Hacker News Reader

No, it’s not. This hurts survey telescopes and it’s an orders of magnitude issue.

A rule of astronomy is that if you can see it with your eyes near a city than it’s really really fucking bright, if you can see it with your eyes in the wilderness after your eyes have adjusted for 10 minutes, than it’s still extremely bright.

Bright, fast-moving things are pretty terrible.

Even if Starlink doesn’t kill astronomy, the next 4 companies with similar deployment will definitely exclude types of sciences and ruin billions of dollars of investments in new observatories.

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First, satellites are only visible in the optical when they are illuminated by the Sun, which is only for a fairly short window after sunset and before sunrise. The exact size of the window depends on how high they are, but most of the good "dark" time should be unaffected.

Second, astronomers already use image stacking to reject any number of transient artifacts, like satellites, airplanes, cosmic rays, etc.

Third, while these constellations are going to greatly increase the number of satellites in orbit, it's only by about an order of magnitude. Yes, that's worse, but it's not like it's a problem that hasn't existed before.

The type of observations that are likely to be most affected are surveys that actually search for moving near-Earth objects, especially near the Sun (and radio astronomy which apparently can detect terrestrial emissions scattering off of satellites) but I fail to see how this will mean anything like "the end of astronomy" (and I have a Ph.D. in astronomy.)

Just to add to this, the satellites can still cause problems during the night after sunset, as they can occlude other objects being observed as they pass overhead.

Half a millisecond of occlusion is enough to cause problems?

Depends on the telescope, but yes.

What happens from birds, soot, bugs, airplanes, frisbees, and clouds?

They don't emit giant amounts of EMR.

Also, almost all of those serious observatory telescopes don't have to worry about. Which is what we are talking about.

I'd love to read an article on how Frisbees are the biggest threat to observing the universe :D

I thought most 'real' telescope exposures were over minutes to hours?

Could describe what such a problem would be in layman's terms?

Terrestrial telescopes, which we've invested a bunch of money in terms of observatories in, receive interference from Starlink satellites. Telescopes in space, like the Hubble, don't have the same problem, but they're on the magnitude of 100x more expensive and its difficult to have the same missions.

Noting that the orders of magnitude increase in cost are directly caused by infrequent launches by launch systems with tight mass and volume constraints, and the need to build a space telescope on the ground, have the equipment survive launch, and then survive with no intervention for a decade or two in space.

As new launch systems like Falcon 9, Starship, New Glenn and New Armstrong eliminate these constraints it will eventually be cheaper to build telescopes in space than on the ground.

Other “pusher” motivations include worsening access to real estate, reduced control over light pollution, recognition of indigenous rights, etc.

This is extremely unlikely, and if it were to happen it is for an extremely small time. I have never heard of this being a practical concern.

Thanks for showing up to be dismissive of concerns that you understand! Nuance is a thing.

correct - I didn't think I meant Starlink would kill astronomy (I thought I was addressing some of the hyperbole rather than extending it) - but probably even at the level to be deployed in the near future we would see severely degraded quality of observations for solar system objects. Furthermore - I do think SpaceX is the "good citizen" here.

I don't think the next 5-10 companies launching constellation satellites will be quite as considerate, so one order of magnitude could creep on to two over 15 years.

I think image stacking has been simulated to work somewhere from okay to unusable even for 15s exposures - I think the trails are actually pretty bad due both due to quantity, velocity in the sky, and brighter-fatter.

It's an area that is plainly in the need for global regulation that currently has none.

Earth shine is a thing.

Not during the night. When the satellite is out of direct sunlight, it also does not see any illuminated part of the Earth.

Saying it will "Kill astronomy" is pretty hyperbolic.

It will likely affect some earthbound astronomy significantly, but much (most?) of the most important work in modern astronomy is satellite based.

I'm on the fence on this whole issue. It's not exactly clear what impact it will have on astronomy. Nor what impact it will have on making the internet pricing and availability. Where I used to live, the only options for internet access were expensive and really bad, the positive impact this might have is potentially quite big.

It's hard with a story like this to suss out what the long term effects will be so it's a big grey area.

Most astronomy is long exposure which the eventual mega constellation is particularly harmful too because there's no way currently to deal with the light reflecting off them.

You know they don't use film plates for those exposures anymore, right? They stack images digitally. Removing satellite trails is the easiest part of the post processing flow, or it damned well should be.

Digit and film single long exposures are functionally identical and for very dim objects you still need long exposures because the amount of light reaching the sensor is very low. You can't image stack if the object is too dim to appear in the shorter exposure's you're stacking.

The amount of important work in modern astronomy that is satellite based is limited, as pointed out elsewhere on this thread.

For now. Do the Elon Musk analysis from first principles. The future of astronomy is clearly outside of Earth's gravity well and atmosphere.

Yes, but the current budgets clearly are not.

He's working on that ;)

/s (jeez, your sense of humor folks...)

Well, he is. For the Luddites in these threads, it's enough to cite the JWST as a reason to keep doing things the same old way, over and over, in space and on Earth.

Of course, the reason why people who enjoy lecturing others about why something can't be done differently or shouldn't be done differently seem to gravitate to a site called "Hacker News" is one of those universal mysteries that can't be answered with a computer or a telescope.

How is that clear? What principles did you use?

Because access to space is insanely expensive.

Don't fight the people who are trying to fix this.

Also dangerous and inflexible.

>It will likely affect some earthbound astronomy significantly, but much (most?) of the most important work in modern astronomy is satellite based.

I'm not an astronomer but I'm not convinced that that's the case. The number of space telescopes pales in comparison to the number of terrestrial observatories. Moreover, advances like adaptive optics have done a lot to close the gap between ground and space capabilities (for optical telescopes). Even once you've invested in expensive tech like adaptove optics, a telescope in space still costs an order of magnitude more than one on the ground (thats being really conservative. JWST has already cost ~10x more than the most expensive ground telescope ever, and the thing hasn't even launched yet)

There were a few space based radio telescopes in the past, but I don't think there are any now. Imagine building something like the Arecibo Observatory[1] or VLA[2] in space. And speaking of the VLA, some of the techniques for getting high quality results (e.g. interferometry without physically conjoining the receivers) are difficult if not impossible to do in space.

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

[2]: 27 of these guys, which are able to move around precisely on rails to generate constructive interference with the different waves they're receiving: https://public.nrao.edu/wp-content/uploads/2016/04/vla_panor...

Can adaptive optics be applied to filter out objects like Starlink satellites?

You can filter them out computationally without adaptive optics with enough frames captured.

Modern astronomy works at the edges of whats possible, a single frame might take hours. Needing multiple frames would mean multiple days per observation. It would mean no longer seeing faint and distant objects, limiting us to younger, closer and frankly far more boring objects. It would make observing variability impossible for certain timescales.

You need old distant objects for cosmology, observing the structure if the universe, big bang and stuff. You need variability for finding exoplanets, measuring distance and observing transitions such as supernovae.

Oh, and then a huge part is taking spectra, which means bouncing the light directly off a grating. Filtering transients is hard to impossible there. You need spectra for relative motion, magnetic fields, composition of matter and radiation and of course temperature.

Needing such filters would set astronomy back a few decades

No, they are too bright and will saturate the detector with even very short exposures. Best you can do is just discard the affected area, at worst you have to discard several exposures because the saturation effected the readout electronics.

Hey you're back! I asked you previously "That might work for imaging, but what's your fix for spectroscopy?" here: https://news.ycombinator.com/item?id=21577081

You replied "Optical, RF, or Xray?"

Then I said, "Let's start with optical." but then you disappeared!

So, what's your solution for long-slit optical spectroscopy?

Hey! I'm still waiting to hear back from the astronomer I paid to do the research. I still intend to report back with their DOI from the resulting paper. I recognize when I've exceeded my domain knowledge and need an expert.

To be clear, I think we're well in the realm of academic discussion; no one is stopping any global constellation due to astronomy concerns. As I've said many times in this thread and elsewhere, I think it's a growth opportunity for the astronomy community to move towards space based observation platforms, and with the plummeting cost of lift (ie SpaceX Falcon and Starship) I don't think that's an unreasonable position to hold.

Don't think so. Adaptive optics works by changing the physical shape of the mirror. If you measure the atmosphere continuously and bend the mirror the right way, you can remove atmospheric distortion from the image. If anything, AO just gets you sharper images of the starlink satellites (or significantly worse ones if a satellite flies in front of the guidestar that you're using as a reference point to measure atmospheric distortions).

> I'm not an astronomer but I'm not convinced that that's the case.

I'm not entirely certain what the balance is here. I don't think my post made it clear that I'm not certain how big the effect would be, only that there is a tradeoff here which is hard to quantify.

I do know there is a lot of significant astronomy done by space telescope and that the importance of space astronomy is only growing.

Seems to me the answer is that those who benefit from the new satellite constellations (SpaceX, etc) should finance additional investment in astronomy to mitigate the effects.

What about amateur astronomy? Are we now saying that only those with the means to afford space telescopes or expensive software can participate?

If SpaceX works out, we'll probably see a lot more telescopes in space. Wouldn't be that expensive at that point for, say, a school class to launch a telescope cubesat.

I'd trade amateur ground astronomy for that.

I'm not entirely sure how you think looking at an image on a computer screen compensates for the experience of doing observations with your own eyes.

There are plenty of good pictures on wikipedia already, do looking at those compare to going out on a clear night and looking at the stars yourself?

A LEO satellite constellation will absolutely not prevent you from looking into the night sky with a telescope and seeing stars.

The dead of night will be fine. But during (astronomical) twilight, the time when you are most likely awake and looking up, it will have ugly extra dots.

What makes a dot ugly?

Also I'm sorry but I really, really don't care about a hobby if it gets in the way of the progress of the entire human race.

Imagine if a painter in Greece in some century BC convinced his fellow Grecians that building a harbor in the cove by their town was a bad idea because it ruined his paintings of the cove. How was he supposed to look at the marine life if you stuck wood and industry in the water???

This. Every change has some negative effect. The question is whether the net effect is positive or negative.

"Seeing a star" is a low bar to pass, especially if you get a telescope to help you.

Are you an amateur astronomer or just trying to be the devil's advocate?

I'd be curious to know what the impact is on impactful amateur astronomy (as opposed to backyard hobbyists who are just engaged for personal pleasure). I know some amateurs use images created by public telescopes, I'm not sure how much meaningful work is done by amateurs using backyard equipment anymore.

Not being dismissive, genuinely curious.

In recent news, the only confirmed interstellar comet in our solar system was found by a dude who worked at an observatory (not as an astronomer) and decided to build own telescope for fun in his spare time. It's one of only two known interstellar visitors we've had, and because he found it early enough the pros were able to make very detailed observations.

A decent number of asteroids and comets are still found by backyard astronomers.

Variable star observing is actually a place where amateurs really help, since it's about observation time, and not necessarily some hugely powerful telescope. And the more powerful a telescope is, the more people want to use it to point at all sorts of things, which makes it kind of expensive to use those telescopes for variable star observations which take a lot of time.

"Since professional astronomers do not have the time or the resources to monitor every variable star, astronomy is one of the few sciences where amateurs can make genuine contributions to scientific research." [0]

[0] https://en.wikipedia.org/wiki/American_Association_of_Variab...

And the Betelgeuse deathwatch!

> I do know there is a lot of significant astronomy done by space telescope and that the importance of space astronomy is only growing.

Former astronomer here. I would argue that the importance of space astronomy is actually decreasing. Satellite telescopes are most important at wavelengths that the Earth's atmosphere absorbs like IR, UV, and X-ray. At visible wavelengths satellite telescopes have been much less important over the past couple of decades due to the development of adaptive optics.

The main reason to put a visible wavelength telescope in space is that you avoid the smearing out of the source by the atmosphere. Adaptive optics solves this problem by correcting for the distortions induced by the atmosphere and bringing images to resolutions that are comparable to (though still not quite as good as) what you can achieve in space.

Since space telescopes no longer have the advantage of much greater resolution, there's much less of a compelling reason to use them for most research problems. (Some questions, of course, can only be tackled by using the highest resolution available.) On every other dimension space-based telescopes are inferior to ground-based telescopes. They are more expensive by many orders of magnitude, much, much smaller, and they cannot be changed once they're up (at least not easily). By contrast a ground based observatory can get substantially better over the course of a year by installing better detectors.

Adaptive optics have zero issues if you’re looking to make a cool picture, but they do introduce bias which is an issue for scientific instruments. That’s largely offset by more and larger telescopes for the same price, but it is very much a tradeoff based in launch costs which are falling.

IMO, over the next 30 years space based telescopes are going to play an ever larger role.

Arecibo and VLA aren't affected by starlink at all. Those are radio telescopes. They don't even need to wait until nighttime to observe. It's only an optical/ir problem.

Starlink uses radio to communicate with the ground. A common complaint from radio astronomers is new radio satellite operators promising to not interfere with radio astronomy and then making no effort to follow through in that promise.

> but much (most?) of the most important work in modern astronomy is satellite based.

You're going to have to point out which source you pulled that out of! As a simple example, more than half of the Nobel prizes awarded for astronomy since 2000 are for discoveries made with ground based detectors. And of those awarded to satellite experiments, none was actually competing with a ground based experiment, so satellites mainly bring different, not better, capabilities.

...ground based detectors...

When I encounter this phrase I think of things like the neutrino detector in Antarctica, which of course isn't affected by satellites at all. How much contemporary astronomy relies on visible-light telescopy?

A very large fraction. Optical is still the most important band, probably followed by radio, x-ray, IR and gamma ray in that order. And less then 10% of optical is done using satellites.

“It will likely affect some earthbound astronomy significantly, but much (most?) of the most important work in modern astronomy is satellite based.”

Not true at all. Ground based is much cheaper and easier to maintain and reconfigure with new and different equipment. Just look at the cost of the upcoming >30m telescopes vs the James Webb or Hubble.

On the plus side, SpaceX is making launches much bigger and cheaper, which will make space-based telescopes much more affordable. Cheaper launches = more, cheaper satellites.

That's good but I am not sure if the launch cost is where the money goes for telescopes.

You are right, but also wrong. Because the launch cost so much you spend even more move on the space telescope because you want it to work for a very long time to get the best value for your money.

And since you are going to spend so much money to launch it, you also add extra hardware to do other type of observations, so the cost of the telescope balloons upward but you are get more bang for the buck.

If on the other hand you have cheap launches then you can send up the minimum telescope needed since you can always send up a better one or even a very different one if you later discover the need.

Today because of high costs, we need to design the scopes to meet all the possible needs we can think of and afford, result very expensive space scopes.

I guess we would have to look at the actual costs and trade offs. Personally I am still not convinced that launch cost is the biggest problem but I am sure astronomers are crunching budget numbers right now and will adjust plans if it makes sense.

A ground-based telescope will always be way cheaper than one in orbit.

Why make this more expensive than it needs to be? Researchers are already strapped for cash.

It will kill astronomy pretty good.

The key point is usable observation time. Our current handful of satellite telescopes provide 24h of time a day. Each terrestrial telescope provides maybe 8h. However, there are a magnitude more telescopes on Hawaii alone than in space. You would need to get a hundred satellite telescopes to begin to replace earthbased observation time.

And that doesn't even begin to talk about the possible instruments, mirror sizes, astronomical costs of buulding and running satellites, etc.

It really won't.

Satellites are invisible if they're in the Earth's shadow. By the time useful observation can begin, there's an enormous swath of the sky that will have zero visible satellites in it.

Diversify your observation targets. There's more than one interesting thing to science at any given moment. If that means spreading out your observations so you spend two hours a night observing four targets as opposed to four hours a night on two targets, so be it.

At the very worst, this means astronomers will need to do more work during the day shift scheduling and prioritizing. This isn't a new problem. I remember reading a back page article in Astronomer magazine sometime in the late 90s with a page of BASIC code. Someone wanted to optimize a computer controlled telescope to make one observation of 100 or so stars every night. You need to roughly minimize the total Manhatten distance between every two observations, while also eliminating observations below the horizon and penalize observations low in the sky. So the author wrote a program to roughly approximate the traveling salesman problem with the additional constraints. In the 90s. In BASIC. In one page. It might be NP complete to get the perfect solution, but good enough is pretty good.

Add an additional constraints penalising observations where they might be impacted by satellites. Hire an intern working on their degree who's taken an optimization course and have them do it for you.

>And that doesn't even begin to talk about the possible instruments, mirror sizes, astronomical costs of buulding and running satellites, etc.

We're going to have to start thinking bigger if we want to leave this rock. Might as well start now.

The real risk is Elon's companies dissolving and the satellites adding pollution for no real gain. If I could trade observatory time for (working) world-wide internet, I'd take the latter with no hesitation.

As much as I sympathize, most of the cosmos aren't really going anywhere. It'll be there after we build hundreds of telescopes.

Starlink is not for consumers, so you cannot get it anyways. It's for enterprise at this point.

My impression is that a lot of interesting "leads" are generated by ground based telescopes and only then examined in more detailed by space based telescopes. If you kill off the generating mechanism, then effectiveness of space telescopes could also decline a lot.

It's nothing really new and the same dynamics can be observed throughout history. Imagine there was a time one could look over and see the bay without the Golden Gate bridge or high rise buildings. And now, its even an iconic thing!

A generation or two in the future astronomy will probably get redefined quite a bit via remote telescopes and adventure vacations to space and so forth.

Even now there are plenty of enthusiasts who are excited to take pictures of rockets during take off or explore satellites as they pass by. So it actually get more people interested in space and astronomy.

And there will always be people on either side supporting or opposing technological advances - as we have seen thought history. The one thing that is certain in my opinion though is that things will change.

OP is talking about affecting astronomy the science, not astrophotography the hobby. Land-based survey telescopes are incredibly useful cheap tools that do not have alternatives.

I guess the argument becomes this:

Does the proliferation of high speed Internet to every part of the world outweigh the cheapness of current land based astronomy tooling?

If not, maybe spacex can compensate by providing some launch load for space bound telescopes.

Ok, then Tesla should really prove they can provide that or find ways to compensate those with land based astronomy tooling. They have done neither and have not communicated in any form that they want to.

tesla?

Sorry, SpaceX, it's easy to get Elon Musk's three card monty of companies confused.

We already have cheap internet where people live via fiber optics. Last mile market failures are solveable.

No, we don't. There are tons of places right around me, in central Europe, where people will benefit greatly from Starlink. A lot of rural-based people are excitedly talking about it, even older people who you would not expect to know what it is - and they don't, but they're excited about their access to the Internet.

This is false

https://www.cnet.com/news/in-rural-farm-country-forget-broad...

Also, asteroid detection may be hampered - there is still a significant contribution of 'amateur' observations to detecting them.

Staring at a night sky in a designated dark sky area is amazing. Given the pace of SpaceX launches amount of time you can do that without sky crawling with LEO constellations is pretty limited. So days of humans experiencing night sky raw are pretty limited (some would argue it is already impossible). However, I think astronomers will find a way to operate even in a noisy environment of mega-constellations. Given that the objects are bright they can be tracked extremely well. Filtering out them out of the datasets does not seem intractable. Am I missing anything here?

Moreover, I think mega-constellations will actually be a boon for astronomy. Think of it as a platform, while initial iterations will be focused on communication systems, what is stopping them from adding sensor packages looking both inwards and outwards? They already have the bandwidth to downlink all of that. Once on the ground those streams could be combined to produce datasets of unprecedented coverage and fidelity.

I think you're missing OP's point:

Once the sun is set in their orbit, they should be invisible both to the eye and telescopes.

"Invisible" isn't quite correct. They won't be visible as white spots, they'll be black spots blocking out the things behind them. Not a big deal for human eyes. Quite a big deal for astronomers.

This is totally false, the solid angle subtended by the satellites is tiny so the effect of their obscuration is totally negligible.

If it's flying in front of the sun, you are correct. If it's flying in front of an object 100 light years away, you are incorrect.

It'd be in front of an object 100 light years away for an absurdly tiny amount of time. The percentage of the sky occluded by these satellites is absolutely minuscule. This is not a rational notion.

These are not geosynchronous satellites, but instead are 200-500 miles above the Earth, moving many, many thousands of mph. No, it isn't blocking anything 100 light years away unless your shutter speed is in the single-digit nanoseconds.

The relative (apparent) motion differences and the fact that the locations of the satellites are known should take care of that, no? It’s unlikely that the motions are going to track each other exactly in most cases.

In fact if, as you believe, these satellites would actually occlude things beyond them, they sound very useful for calibration and education.

The satellites are not only small, they are also fast. A fast moving satellite can only occlude a 100 light years away object for a couple of microseconds before it passes. This is absolutely negligible for an astronomical observation lasting seconds to minutes. And even if you launched billions of opaque satellites they couldn't come close to blocking a big enough percentage of the sky for this to matter at all.

There go my hopes for an effective planetary sunshade in LEO...

That should probably be at L1 anyway.

That's where it can shade 24h/day.

It'll block a star for ~1/2500th of a second (assuming a three meter blocking radius, and 7500m/s) - I wouldn't be surprised if that went undetected 99% of the time. At most it would read as a minor brightness fluctuation, right?

Not only that, but it first has to actually pass in front of the star. This gets increasingly likely as you look at fainter and fainter stars, but the sky is still mostly empty and is not as common as you might think. (Olber's paradox and all that.)

It's bright because it's in a low orbit and a lot closer to us. Because it's in a low orbit it's in the earth's shadow for most of the night. It's not bright while in shadow.

> Bright, fast-moving things are pretty terrible.

Why is that? Almost everything astronomy studies isn't fast-moving. Shouldn't it be easy to filter out that noise?

This is what I'm wondering. It seems pretty trivial to filter out with some basic image processing.

I think there are 2 issues here, and it's making the conversation around it difficult.

First is the impact to "professional astronomers", and from what I've seen this group won't be impacted nearly as much as the other. This group has the ability to use satellite based telescopes, or has the tech already to be able to filter/post-process the images to remove satellites, planes, meteor showers, and any other stuff that might get in the way.

Then you have "amateur astronomers", this groups is likely to be impacted by starlink. This group doesn't have access to the digital filtering stuff that the "big guys" do, from what i've seen, most of the people in this group just use normal long-exposure setups and adding in a processing step would mean a pretty significant change to their process, and probably a lot of additional costs.

Even still, the impact to amateur astronomers seems limited to when the sats are in sunlight, which traditionally isn't a super popular time for stargazing (although I may be wildly wrong on this, as I've read that these sats are removing up to 1/3 of the normal viewing time for some astronomers, so don't take this as gospel), and I still think the impacts will be a lot less doom and gloom than some are saying, but I still hope that SpaceX can work with the astronomy community to see if there are solutions or mitigations that can help everyone out.

We absolutely use short exposures. It's actually more important for us than the pros because the mounts are a lot less stable and polar assignment is far worse. Doing a lot of short exposures is a lot easier than nailing your polar assignment. It also help with bad seeing; you throw away the blurriest quarter of your images and the stack looks a lot better.

Filtering is less advanced, but masking outliers (and their neighbors) and replacing them with an average of the others isn't advanced filtering.

It's annoying the way getting cut off in traffic is annoying, not the way getting T-boned is annoying.

Everything is "trivial" when it's someone else's problem.

That’s 100% true!

So, you clear your CCD, collect photons for 30 minutes, then some satellite sprays you with a multiple of the number of photons collected thus far, and then ... what?

Instead of exposing for 30 minutes, astronomers take lots of shorter exposures and stack them. Otherwise you'd get tons of noise from CCD hot spots, cosmic rays, aircraft, meteors, satellites, etc.

Well, but then, you also get noise from CCD readout, so it's not like you can just take 18000 100ms exposures and stack them to get the same result as a 30 minute exposure minus the "broken frames". Stacking frames is a workaround for disturbances, but it comes at a cost in the form of readout noise. The shorter you make the exposures, the more disturbances you can filter out without wasting observing time, but the more readout noise you get. So, if you have more disturbances, you either need more telescope time so that you still have enough frames left to see your signal after you have thrown out all the bad frames, or you need to reduce exposure times so you can throw out frames as higher granularity, but then you have to accept more readout noise, which makes it harder to see the signal.

There are already enough disturbances that a 30 minute exposure is impractical. Astrophotographers tend to use exposures around 30 seconds. It's true that more satellites mean that astronomers will have to tweak their observation methods and/or reduce their observation windows, but it's not a showstopper. At worst it's an inconvenience to them.

If we were to employ the reversal test[1], the concern about astronomy would be a non-problem. Imagine if the entire planet was covered by the equivalent of 4G cell networks. And imagine if some astronomers asked us to destroy those networks so that some of their work could be made more convenient. Imagine all of the people affected by this network. All of the lives saved by emergency calls, all of the remote locations made digitally accessible to the rest of humanity, all of the scientific experiments in jungles, deserts, tundra… cameras and microphones and sensors reporting data through this global satellite network… imagine all of that destroyed so that some astronomers could be relieved of an inconvenience. That is absurd. Yet that is the world that some people want to live in.

It's so clear to anyone whose view isn't so parochial, so local in time and space, so blinkered by where and when they were born. Does anyone think that astronomers will still be preventing the launch of satellite constellations in the year 2100? In 2200? In 2500? Clearly not.

I'd rather the improvement happen in my lifetime than after. Launch away.

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

Bright = overexposure or unmanageable dynamic range

Fast-moving = more likely for it to traverse your field of view while the shutter is open

Is there any way, perhaps with software, that we could remove a moving object, from an otherwise mostly static set of images?

Absolutely, in fact it's pretty easy and is routinely done by amateur and professional astronomers alike. We've had satellites, airplanes, and meteors obstructing astronomical images ever since we began taking them.

A very simple and common way is to stack all of the static images aligned on top of each other such that you have a set of values for each pixel corresponding to the same region of sky. Then sort the values of each pixel by brightness and keep the median value for that pixel. Or throw out that top and bottom 10% and average the rest, or throw out the top and bottom N, etc.

This is a standard feature of essentially all astronomical image processing software and has been for a long time.

Sure. But increasing the number of frames with tracks increased the number of datapoints you need to throw away, reducing the effective time on target and therefore sensitivity of your observations. Astronomers are not idiots. They know how to deal with obstructions. But that is not free of cost. Neither in observational limits nor computer time nor required brain power.

Sure it's not without cost, but in most cases the cost is not very high.

Remember you don't need to throw away the whole frame, only the pixels that were obstructed. One track across a frame will obstruct less than 1% of the data in that frame.

One of the key assumptions that's being made, throughout this thread, is that astronomy is mostly imaging. Taking or stacking images. A ton of astronomy is spectroscopy, which is nothing like a stack of static images with one that has a streak in it.

Could someone explain what the actual tangible negative implications are besides astronomers needing to adjust?

Personally, I don't want to be limited to observing the stars from planet Earth for too much longer. The development of commercially viable space technology will fund and fuel investment in interplanetary expeditions and help us move to the next stage of human progress.

Could you explain how something that orbits 500km up could be seen at night?

Like most other satellites, it can be seen when it reflects the Sun. Satellites tend to be shiny. For an extreme case, check out "Iridium flares" - a brief but bright flares on the sky caused by old Iridium satellites, whose antennas were essentially large, rectangular mirrors.

To reflect sunlight you need the sun. If a satellite is 500km up (and 300km for later revisions), there is no way for sunlight to reach it.

There is no way to see Starlink at night. You can potentially see them for a short period around twilight.

You've really never looked into a night sky and seen a satellite? Unless you live underground or never leave a big city, it's quite easy and there are dozens of apps that will help you understand what you're looking at.

I guess the point they are trying to make is that 500km (or 300km) is essentially hugging the planet. Which means that, if it is night, they will be in the shadow for the majority of the time.

The satellites you can easily see at any time are much higher up.

> There is no way to see Starlink at night. You can potentially see them for a short period around twilight.

The time window is limited, yes. So it is not the end of the world. It is still a problem.

Here is the actual geometry at the equator, ignoring axial tilt (the blue/black circle is Earth, the red/black circle is a satellite at 500km, and the radial lines are hours): https://www.desmos.com/calculator/3br1snafmj

Starlink satellites directly overhead are in sunlight for about 1.5 hours after sunset, and the same before sunrise. Including observing on an angle, you probably lose 4 hours per night out of 12. With 300km satellites, you probably lose 3 hours. I think the situation will be worse away from the equator in summer.

Depending on the type of measureme t taken, a dark transient is also harmful. However, by far not as bad as a bright transient.

A shortsighted attitude, IMO. Terrestrial observatories are in a good position to clean up satellite artifacts digitally. They already have to do more image processing than the staff at Playboy. Meanwhile, cheaper access to orbit can only be a good thing for astronomy, given that we've picked most of the low-hanging fruit in terrestrial-bound optical observations.

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