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Comment by superposeur | Hacker News Reader

Do you know what advantage Euclid offers over Webb?

Also, the Lagrange point is where Webb and some other stuff is located — is it getting crowded up there?

It's not really about one being better than the other, just that they're designed for different purposes. Euclid is a survey telescope built to research dark matter, for which it has a large field of view so that it can build up a picture of the entire sky in all directions. JWST is focused more on investigating the early universe, for which it has a much larger primary mirror (gather more light), but has a lot of other capabilities as well.

Euclid has a much smaller primary mirror, and its spectroscopy capabilities are limited compared to JWST (it doesn't need all the same bells and whistles). It also can't observe as far into the infrared as well as Webb. However, as stated, it has a wide field of view and enough photometric color and spectroscopic resolution to do it's main job of measuring galaxy shapes and positions and their redshifts in support of investigating dark matter.

Euclid is a survey telescope so closer to the Nancy Grace Roman telescope which might be sent out around 2027.

https://www.nasa.gov/missions/roman-space-telescope/nasas-ro...

There is also another earth based sky survey telescope, the Vera Rubin Observatory up next year. That one is kind of interesting because it will produce a massive amount of data with data processing to detect if an object in the sky changed brightness or position over time and send out alerts to scientists or anyone else interested.

https://www.lsst.org/

Back when 10TB was enough space for the entire Sloan survey, Vera Rubin Observatory was expected to produce 1TB every night. They dug a trench up into the mountains to lay a fiber optic cable specifically (and only) for Vera Rubin.

Not to quibble but it is an even more mindboggling 15TB/night.

https://www.ipac.caltech.edu/project/rubin

Haha, it must be inflation. Back when I was involved the 1TB number was the one being thrown around. Thanks for posting that link. IPAC is really doing well for themselves with all the new projects they're hosting.

That must be it! A few years ago, an old high school chum who works on the Rubin also mentioned the 15TB number. I neglected to ask if that was raw FPA output that would be processed down to smaller sizes or sent as-is. The project has been going for a while so maybe the technology to do it became practical in the interim? Whatever they do send, it is still an astronomical amount of data. I'll show myself out.

Lsst.org is now saying 20TB, or ~ 60 Petabytes for the whole run.

JWST is observing the infrared only and has a narrow field of view.

Euclid is wide-angle with both visible and infrared capabilities.

Thanks — is there a short answer to what can wide angle get you?

Literally what it says - a wider field of vision. Read the text on the ESA page.

Euclid aims at measuring the shape of as many galaxies as possible to observe statistical effects that let us draw conclusions about the dark matter distribution

A wide angle lets you image something like the Andromeda galaxy or nebula all at once in the same frame.

A narrow angle is more "zoomed in" so to image a larger structure you'll need a lot of exposures and build a mosaic. It takes a lot longer which means you have to monopolize the instrument for a long time.

If you want to image large structures like galaxy clusters a wide angle telescope is more efficient. Since the lifetimes of telescopes are limited (fuel, coolant, etc) you want to spend that time getting the most data out of the instruments.

Not that you're wrong, but galaxies in our neighborhood aren't really of concern to Euclid. The mission is to determine the expansion history of the universe, for which we will observe billions of galaxies. The handful of galaxies in our local group, which don't contain any information about the expansion history anyway, are less than a drop in the bucket.

Also, frames can just be stitched together if necessary. And Andromeda is larger than the field of vision of Euclid.

A large field of vision just helps you cover a large amount of sky in a reasonable time frame.

Star/galaxy surveys.

For example there were a bunch of articles recently about 'stars disappearing'. That's because we take snapshots of wide ranges of the cosmos every once in a while and compare them. We can use this to figure out the direction and velocity of stars in our own galaxy. And in some cases things appear and disappear that are rather unexpected. You don't get that from narrow angle photos.

More data. Euclid is for filling databases with survey data covering large-scale structure in the universe. Webb is for looking at very small, very distant single objects. Two different instruments for two different experiments.

Consider comparing a fancy DSLR with a telephoto lens to a night vision security camera. Each does what the other can't, and you deploy them for different tasks.

Should also note that "wide angle" is very much relative and in this case means "about the apparent size of a full Moon in the sky" – so vastly different from what a photographer would mean by "wide angle" =)

it is a telescope after all, so of course it's going to be scoped in. anyone confusing wide angle photography with a telescope is just not comprehending concepts very well.

Eh, yes, because this is not an astronomy forum, there may be plenty of people who don't have a good idea of what "wide angle" means in that context. So IMNSHO a clarification was entirely appropriate, and thinking otherwise is rather arrogant. I didn't mean that "wide angle" would mean something like a 24mm camera lens, but more that it's much more narrow than even long telephoto focal lengths like 200mm or 400mm or even 600mm!

Especially given that this is a survey mission whose purpose is to image large parts of the sky, it could be entirely plausible to a layman that its angle of view were much wider than 0.7 degrees!

How's the Nancy Grace Roman Space Telescope compare to Euclid?

Euclid has visible imager and near-infrared spectrometer and photometer. Webb is all infrared. So they have non-overlapping missions even when observing the same structures and objects.

Also space is very large. The L2 orbit is gigantic and the probes are teeny tiny in relation. So it's hardly crowded in any sense.

I'm sure crowded is far off, but it's still interesting to think how they interfere with each other's instrumentations (given the field of vision is immense in comparison to their size), is there some type of space control traffic involved?

The L2 point is about 1.5 million kilometers from Earth. The various probes like Webb and Euclid orbit around that point at (IIRC) about a million kilometers. The various probes in that orbit will effectively never interfere with each others instruments.

As for coordination, at that orbit, it's going to likely be the individual agencies coordinating with one another. Every probe/satellite launch gets COSPAR IDs and other tracking IDs through various national and international agencies.

More on L2 orbits https://webbtelescope.org/contents/media/images/01F4STZH25YJ...

Good find, I was looking for a similar (or maybe that) image for illustration. It's a good description and illustration of Lagrange orbits.

What advantage does a flatbed scanner have over a polaroid camera? They both capture light, but with different optics and for different purposes.

Copy and pasting a previous comment: https://news.ycombinator.com/item?id=36558940

Euclid is a deep sky survey space telescope. Like many space telescopes, it's designed to run cold (-140C) to extend viewing into infrared bands ground telescopes can't access. Being a sky survey instrument, it has a wider field of view than Webb, 0.5 square degrees versus 0.0025 sq deg.

It's something of a follow-on to ESA's Gaia astrometry space telescope, which surveyed the entire sky out to visual magnitude 20 and in 320–1000 nm light, while Euclid will specifically examine the 15,000 square degrees of the sky the Milky Way doesn't cover, out to magnitude 24.5 and in 550-2000 nm light. Both dimmer and more redshifted. (Fun fact: both Gaia and Euclid are made largely out of silicon carbide, including the optical bench and mirrors, which has become a ESA specialty.)

For another comparison, the first Sloan sky survey (using a 2.5m ground based telescope much bigger than Euclid) took 5 years to image 8,000 square degrees down to magnitude 22.2 and only out to 893 nm. Again, Euclid can see objects dimmer and more redshifted.

These press photos are of large, interesting objects, like nebulae and nearby galaxies. Amusingly enough, though, for Euclid's mission these are obstructions, which are getting in the way of all the dim smudges in the background that it's actually supposed to be capturing. A cloud passing in front of a mountain you're trying to take a picture of. We'll either need to send another telescope a thousand light years away to image them, or wait thousands more for Sol to travel along its orbit in the Milky Way and move them out of the way.

>Also, the Lagrange point is where Webb and some other stuff is located — is it getting crowded up there?

For stability reasons, spacecraft orbit around L2 rather than sitting at its center. Here's a diagram of JWST's orbit: https://i.stack.imgur.com/sBH2i.png It's a bent ellipse that's 1.6 million km in length along the long axis, considerably larger than the orbit of the moon. You could put three million telescopes on that orbit and they'd each be a kilometer apart.

Thanks and great diagram — I’d imagined a tiny orbit around L2, not one the size of the entire earth!

The diagram does not make this clear at all, but the big circle is the orbit of the Moon. The Earth is only 12,756 km in diameter, and the tick marks are 200,000 km apart. If drawn to scale on that diagram, it would be 2.7 pixels wide.

Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen...

the word point used with Lagrange is bit misleading if you're thinking of it as an actual point. The satellites at a Lagrange "point" are actually orbiting the point like it is a NULL pointer in a 3D app (if you have familiarity with that concept). Also, space is big.

It images a large patch of sky in 600megapixels at once. It's an overwhelmingly more valuable telescope by how much it gathers at once, JWST only captures a tiny dot, in similar resolution.

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