Giant, all-seeing telescope is set to revolutionize astronomy | Hacker News Reader

Giant, all-seeing telescope is set to revolutionize astronomy

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192 pointsgammarator67 comments

I have been working in astronomy for a few years now and I recently have gone back to school for a PhD in orbital dynamics.

Rubin is going to make a big difference in our knowledge of the asteroid belt, it will likely more than triple the size of our known catalog of asteroids. Its actually somewhat difficult to know exactly how much it will increase our knowledge. The bigger the telescope we build, the fainter the asteroids we see. The difficulty is that while we can make a pretty educated guess as to how many smaller ones there are, this is such a jump that the error bars on that guess is quite large. I am quite excited to see how the catalog of asteroids changes, I expect we will be finding a LOT of smaller rocks near the Earth.

Asteroids have a broad range of albedo, basically the brightness of the surface can vary from the blackest coal (like 3-5% of the light reflecting) to concrete (up to about 50%). All visible range telescopes will be susceptible to a bias in their observations, since a big black rock will be as bright as a smaller paler rock. We know that the asteroid belt favors the dark material.

In a couple of years, the Near Earth Object Surveyor (NEOS) space telescope will launch. NEOS is an IR telescope and will not have the same albedo bias. The trade off is that it will measure the black body radiation, meaning asteroids have to be nearer the sun. Broadly these are very complementary surveys, Rubin will be fantastic for filling out the main belt, and NEO Surveyor will do a great job on our neighborhood.

Source: I worked at Caltech on NEOS, I wrote the code they use to predict known asteroid orbits:

https://github.com/dahlend/kete

Edit: I failed to mention that Rubin is a big deal for a lot of time-domain astronomy, I'm just being selfish talking about asteroids only.

I love your selfishness. Learned a lot, while sipping my second coffee and eating my breakfast before diving into work. Thanks kind stranger.

I loved astronomy as a kid and the town I grew up in has a "solar system way", basically a long street where a kind fellow (who in his freetime taught astronomy to nerds like myself and had built his own oberservatory in his backyard) had - with the blessing of the city - built a scale model of the solar system on a length of about 1.5 kilometers (a bit less than a mile).

I always found it fascinating when walking "through our solar system" with about 13 times the speed of light (normal walking translated into the distance at that scale) how veeeeeeeeeeery far apart things get in the solar system.

Sadly only in German: https://www.muenchberg.de/erleben/tourismus/tourismus-und-fr...

Edit: And yes - Pluto is still in there. It was built before the demotion - and they kept him in when doing the renovation last year (I was not in my home town since then - I so need to see it, when I visit the next time).

Selfishness tends to work well for everyone when practiced by a rational individual ;)

I’m pedantic: s/rational/romantic|idealist|not-cycical-person/

No need for all that extra stuff, just be rational enough to realize humans do not exist in a vacuum, and trust those feelings that tell the healthy mind to be kind, and indeed, that other have those feelings too.

Not pedantic enough. You failed to define cycical, which may be a misspelling of cyclical, but is impenetrable in meaning if so.

Or maybe it's a typo of cynical rather than some craziness.

Good luck with cleaning out the Musky foreground!

Took me a bit to derive "Elon-Musk-created" from "Musky".

In the meantime, I imagined high-jumping muskelunges...

For anyone passionate about orbital dynamics: IMO it would be great to get more eyes on and thorough critiques of the Tychos model put forth at https://www.tychos.space where there is a book, visual simulator, forum, etc.

The sincere claim put forth appears to be that Tycho Brahe was almost right, and that something like this is in fact true:

  - The planets except for the Earth orbit around the Sun
  - The Sun orbits around the Earth
  - The Earth has its own small orbit

It is pretty dense information, but seems important if true. I believe that the Tychos model is claimed to be just as consistent with observation as the conventional model, if not more so (with some arguments in the favor of the Tychos model as more likely, which escape me).

The best intro to cut to the chase may be at https://book.tychos.space/chapters/4-intro-tychos but I think that the writers would do well to summarize their main arguments somewhere.

What is this, flat Earth theory for people with bachelors degrees? There is a 0% chance this is true.

It can seem that way. They are more or less ultra-realists and ultra-skeptics.

Here's a 1-page abstract from the 2025 Demysticon conference: https://files.catbox.moe/j8rd0s.pdf

An excerpt from the abstract is below, listing some issues they have with the mainstream heliocentric model, which are presumably resolved elegantly by the Tychos model:

  Anomalies of the Keplerian/heliocentric model include:

  1: whether the Sun has a binary companion,
  2: why only Mercury and Venus have no moons,
  3: why Venus always presents the same face to Earth at its closest approach,
  4: the “anomalous” precession of Mercury’s perihelion, and other aspects of Mercury and Venus,
  5: the cause of the General Precession (Newton’s lunisolar wobble theory is not it, it does not match with observables),
  6: why Mars and Sun exhibit 79-year cycles locked at a 2:1 ratio (and many other “harmonies” found between bodies),
  7: why there is a sidereal diurnal variation of G, in interferometry results, and in the movements of stars,
  8: why sunspot formation location shows a geocentric preference, and more.

A small error in a simplified (non-relativistic!) model does not in any way imply the truth of its diametric opposite.

PS: I find it entertaining that I can judge the crackpot level from the URL itself without even having to click it.

If you're just here looking at the HN comments: check out the article. It's really well-written and has a bunch of nice visualizations if you like astronomy things.

The last picture made a bit sad and feel pity for astronomers : "Satellite swarms mar Rubin’s pristine view"

I imagine these are like mosquitos in photoshoot where you try to capture a super hot model.

I guess Rubin will be the last telescope built on the Earth surface right? Little use to have stronger eyes only to have them blinded...

Building telescopes in high-earth or solar orbit has other advantages too: you can make them much bigger, and don't have to account for atmospheric distortions, etc. The downside is cost of launching them, but the same SpaceX that's 'ruining' the images is also making it much cheaper to launch them into space.

I visited there a few months ago, and satellites are not a big concern for Rubin in particular. It will visit every part of the sky over 800 times and add all those images together, and since the satellite trails won't cover the same things every time the overall impact on data is minimal. They estimate less than 1%, so the plan is to just run the survey for 1% longer.

Discussion a year ago (75 points, 22 comments) https://news.ycombinator.com/item?id=39927682

The mirror coating timelapse video is pretty awesome https://www.youtube.com/watch?v=Gg9UPS7ndRA

Why is the substrate glass? Lack of reactivity? Ability to remove imperfections? As a layman with almost zero knowledge of telescope construction, I feel like a heavy amorphous solid would not be my first choice for the base layer underneath the reflective/mirror coating.

Its not your normal soda-lime glass, its more of a glass-ceramic material that have very low coefficient of thermal expansion, something like zerodur: https://en.m.wikipedia.org/wiki/Zerodur , which means it can keep its shape and focus even under varying temperature

Interesting demo by Huygens Optics: https://youtu.be/qi8jmEbWsxU?si=rj0I3k-l74Xhg7vC

I think while the smaller mirror here is Zerodur, the larger one is just borosilicate,

https://astro.arizona.edu/news/rubin-observatory-achieves-an...

That would be an odd choice.

A large glass mirror once cracked because they "only" allowed one year for it to cool.

The second one was allotted three years.

I see some parallels with magnetic resonance imaging. I worked on a project optimizing MRI scans a few years back. I remember the PI in the project essentially acknowledging that analyzing single MRI images is absolutely more art than science, but there's a ton of value in getting periodic MRIs (say yearly) and looking at the diffs. I imagine a lot of the value coming from Rubin will be due to this, as well as the reason it was built for speed.

The starlink streak issue is real, but isn’t this type of survey uniquely well suited to compensate for it, because it takes repeated exposures in relatively quick succession, meaning the odds of a given pixel being obscured by a streak in successive images get very low? Still not ideal but seems manageable compared to other telescopes running non-automated surveys.

As I understand it, the orbit for each satellite is very precisely known.

Which I think/hope means you can remove/identify known satellites in the images mechanically.

That doesn't help if the distant light you're interested in was blocked. It's not an aesthetic concern. You can't remove the satellite and put the interesting light back. It's just gone. That could be a supernova or some as yet unidentified phenomena that only exists for a moment.

It's gone for the very brief moment the satellite blocks it.

The article says Rubin pictures are 30 seconds exposure, which should leave at least 29* seconds of data.

Of course, there will unavoidably be some degradation.

* This number is backed solely by my personal intuition

That’s not how it works, especially for Rubin. In practice what it means is much lower statistics on streaky data over time. The streaks are not point sources either, so they have a disproportionate impact. You can deal with this through survey strategy to some extent.

You can almost think of this as something similar to vignetting in the final data products. Certain areas will have lower statistics and especially lower temporal resolution based on the season depending on where they are relative to the horizon near twilight.

So, a single image could be lost, but there is supposed to be 1000 or so good images of that area over the survey, about 100 a year. With the satellites, potentially you’ve now lost 3–8 images a year for any given section of the sky (probably more near the equatorial plane), lowering your statistics of the entire survey 1-10%, depending on the declination.

I’m spitballing numbers, there are actual papers you could read though.

Rubin is “wider, deeper, faster”. This reduces all of those dimensions to some extent, but especially the deeper.

That fits with how I was thinking of it. I had something like this in mind: https://www.sciencealert.com/galaxy-speared-with-black-holes...

Galaxies are tiny little things in a telescope's view and a satellite always in that view, even if it's only one out of so many shots, could make it harder to glean useful data from an interaction between two galaxies like that. That beam is moving at near the speed of light and a telescope like this could tell us if there are fleeting but significant changes in all that power interacting with matter. Unless a satellite interferes with that light at just the wrong time.

Is there a figure somewhere on how many TB of images this will produce per day when running in automated sky survey mode?

> The vast archive, growing by 20 terabytes each night, will after 1 year contain more optical astronomy data than that produced by all previous telescopes combined.

73 PB over the full runtime of the survey. That’s a nice new datacenter filled to the brim with images.

Probably about 10 racks if using dense HDDs.

Storage densities these days are kinda amazing, it's not that much of a datacenter. Assuming you chunk it with triple redundancy, that's 220k TB raw. 10k 22 TB disks, you put them in one of those 4U 50 disk storage pods. 200 pods, 10 of those in a rack with some space left for a switch and power, so that's only 20 racks.

Only 50 disks? WD sells a 102 disk 4u box and Seagate sells a 106 disk one.

The Rubin Observatory will generate approximately 20TB of raw image data per night, with an annual data production of about 15PB for the 10-year survey.

I found this pdf presentation with lots of great technical details about data management and a devops infra oriented view of this telescope: https://ci-compass.org/assets/602137/2025jan23_cicompass_rub...

Worth a read for the devops guys around here!

  - about 20TB per day, around 100PB expected for the whole survey
  - 0.5PB ceph cluster for local data
  - workloads on 20 nodes kubernetes cluster/argocd
  - physical infra managed with puppet/ansible
  - 100Gbs(+40Gs backup) fiber connection to US-based datacenter for further processing

Insanity - love it

If you think this is insanity I encourage you to look up the expected data to come out of the SKA. Even after several processing steps they expect several hundred PB/year (the raw data which is not being archived is several orders of magnitude more). That is only SKA-low I think for SKA-mid we are talking Exabyte/year. I recall that their chief scientist said once they are operational they will process more data than google and facebook combined.

Yeppers: https://en.wikipedia.org/wiki/Square_Kilometre_Array

In-page search for "data challenges". Pfew, that's a lot of data.

I wonder if they could reduce the data size at rest by using specialized compressing techniques. Your probably could build an averaged "model" of the sky observed by the telescope (probably with account for stellar parallax and bright planets) and store only compressed diffs, not full images.

But I guess, since storage is relatively cheap, it's simply impractical to bother with such complexity.

There's quite a bit of black out there. That should compress easily.

The usual lossless image compression algorithms is the given. I am talking about compressing it further since the telescope observes the same (or largely overlapping) patches of the sky and the most significant signal is stars, which are more or less "constant". At the very least, they probably could use the lossless "animation" compression algorithms like APNG or FLIF for consequent images of the same sky patch.

Look up fpack and funpack.

actually the telescope devops guys were hiring a couple years ago on HN: https://news.ycombinator.com/item?id=38101085 :-D

Holy shazbot! I thought the author was being a bit hyperbolic about the "built for speed" part...

"The test drive shows off just 20% of Rubin’s maximum speed. At full tilt, a runner wouldn’t be able to keep up.

Presumably measured at the edge of the platform, but still... WOW!

Q for astronomy people: This is tracking the sky movement as it takes the pictures right? Also, with the atmosphere moving, is there a limit of how large the telescope can be and take photos from earth, before it can't get more quality?

The atmosphere is always an issue, we can correct for many of the effects using adaptive optics, but there are always limits. The advantage you get from going bigger on the ground is that you are making a bigger "bucket" to put photons in. More photons = fainter objects are visible, this is the motivation for projects like:

https://en.wikipedia.org/wiki/Extremely_Large_Telescope

Typically for non-adaptive optics telescope the atmosphere will limit you to the scale of about an arcsecond. Meaning objects which take up less than an arcsecond of the sky will appear as points. Adaptive optics telescopes however have much better resolving power.

The seeing in Chile is closer to .7 arc seconds. Sub-arcsecond seeing for Rubin has already been achieved across the focal plane.

As I said, just an order of magnitude estimate for many non-adaptive optics telescopes.

At some point you'll be diffraction limited even at the scale of Earth. The larger your effective aperture, the better you can resolve. Adaptive optics helps get big telescopes closer to diffraction limited performance. That's the best you can do with a given optical system, barring some funky microscope setups. Trying to beat the diffraction limit has occupied a lot of very smart minds.

https://en.m.wikipedia.org/wiki/Diffraction-limited_system

Practically to go really big you need to use interferometry. There are radio experiments that can do this at Earth scale - the Event Horizon Telescope can image very small objects (black holes) by making simultaneous observations from all over the world. The telescopes point at the same place and use very very good timestamping. At the South Pole we have a hydrogen maser for that. Then all the data gets sent somewhere for correlation and a lot of processing. The analogy I like most is imagining you have a big mirror (Earth) but you've blacked out almost the entire surface except a few points where the telescopes are.

Radio is particularly amenable to this because you can build big dishes more easily than for visible light, and the diffraction limit is lower because it's proportional to wavelength/aperture. So in addition to big dishes, you're observation wavelength is much much longer (mm vs nm).

There's a log-log plot on that wiki page which is quite difficult to read, but the important point is that radio is all the way at the top and the best we have is the VLBA.

Visible interferometry is much harder...!

it tracks the sky. The exposures here are never longer than 30 seconds for the normal survey mode. They bounced around a lot, it was going to be 2 15s images so you can do cosmic ray rejection (and other things)

I visited the cleanroom where they manufactured and assembled the lens and processing unit before shipping to Chile. world’s largest digital camera at 3200-megapixel image in a few seconds.

Has this not been affected by USA science cuts?

It's been over 10 years since they started. I don't know what the funding details are, but overall this is not really working on a scale that 5 months would change.

It looks like the current administration may kill other projects mid-mission:

"Among the other programs set to lose funding are a craft already on its way to rendezvous with an asteroid that's expected to pass close to Earth in 2029, and multiple efforts to map and explore the acidic clouds of Venus. Researchers worry that abandoning missions would mean investments made by earlier generations might be lost or forgotten."

https://phys.org/news/2025-06-trump-dozens-nasa-missions-thr...

So I'm not sure any US government-funded science project is safe.

The time the tree has spent growing is only loosely correlated with the time it takes to fell it.

No, but its space-based counterpart was cancelled (the 2.4 meter wide-field survey telescope).

https://en.wikipedia.org/wiki/Nancy_Grace_Roman_Space_Telesc...

It has not been cancelled as of now, the cancellation has only been proposed, not passed.

> alerts for each new “transient”—as many as 10 million every night

How are astronomers going to deal with that many alerts?

There are automated "alert brokers" that will filter these alerts to make them manageable- you can subscribe to phenomena that you're interested in and get only those alerts.

This sounds so cool. I sure hope this isn't one of the projects threatened by impending cuts to science funding.

I suspect the better question is "how badly affected are project science goals by the funding uncertainty". I'm not US-based, but from what I've heard no astro projects are unaffected.

fictional question: how much detail would we see if we could somehow make a telescope with a 1 million km diameter

Not exactly the same, but https://en.wikipedia.org/wiki/Very-long-baseline_interferome... is a technique used in radio astronomy which uses two receivers a long way apart and a very accurate clock to approximate having a radio telescope the size of the distance between them. By putting one receiver on a satellite, measurements have been made with a separation of 300,000km.

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