# Tag Info

72

It's cheaper. (1) With adaptive optics you can get 0.1 arc second resolution on the ground (admittedly only on a mountain top with particularly good air flow, but still!). This eliminates one of the major advantages of space until you get above several meters mirror diameter. (2) Rocket fairings are the shrouds which protect payloads during the supersonic ...

63

It's a problem because there are still lots and lots and lots of ground-based telescopes. Ground-based telescopes are still (by far) the biggest optical telescopes, and the cost of space telescopes is prohibitive for many research projects. It will be a long time before a telescope anywhere close in size to the VLT can be launched. Most space telescopes are ...

21

Large masses can bend light, but space is largely empty. The light from distant stars and galaxies rarely passes close enough to another star or galaxy to have deviated. On the few occasions when it does, it is special and notable. For example, the Einstein cross looks like four quasars in a (very small) square, with a galaxy in front of it. In fact it is ...

20

Your first question - is JWST going to orbit Earth - is a little complicated. It will follow a mission profile that will send it to the Sun-Earth $L_2$ Lagrangian point. It will take the telescope about three months to achieve its orbit in $L_2$. Now, $L_2$ is unstable, and so some station-keeping - essentially, course corrections by thrusters - will be ...

19

Hmmm no, it wouldn't be cluttered with debris, and yes, it's a good idea to park the JWST (James Webb Space Telescope) at the Sun-Earth L2 point. The five Lagrange points are unstable, for one because of the gravitational anomalies of the two massive bodies of the Lagrange system, eccentric orbits, and there are many other factors to their instability. At ...

17

In addition to Mark's great answer ... Why are we building larger land-based telescopes instead of launching larger ones into space? If you had money for two homes, one near work and a 'summer cottage' in the woods, how would you divide your budget? This question is a follow-up to Do bigger telescopes equal better results? Yes, and I'm not a fan of ...

15

To expand on the "space telescopes are expensive" aspect: Space telescopes cannot be maintained or repaired. This applies not just to things like optics and instruments, but also to space-specific equipment like gyroscopes and thrusters (the James Webb Space Telescope has an estimated lifetime of $\sim 10$ years, set by the supply of fuel for the ...

14

All "big" instruments have observation logs, so does Spitzer. The complete logs are here but there's also a filtered log for solar system observations which shows basically all planets and especially many minor planets. That said, it's not a general sky survey telescope due to its FOV of 5' x 5', so it's not meant to discover objects in ...

13

It's complicated. Until late-20th century, we've tried to make bigger and bigger monolithic telescopes. That worked pretty well up to the 5 meter parabolic mirror on Mount Palomar in California in the 1940s. It kind of worked, but just barely, for the 6 meter mirror on Caucasus in Russia in the 1970s. It did work, but that was a major achievement, for the ...

10

A handful of space telescopes are located in Langrange point L2, 1.5 million km from Earth. This is much farther away than the Moon, and far outside Earth's atmosphere. WMAP and Planck, which measure the cosmic microwave background (CMB), are located here because Earth is a hundred times brighter than the CMB in this wavelength region. Herschel observes in ...

10

Currently New Horizions is temporarily hibernating; it's last activity was two months ago. So I'm going to post a supplementary answer here because it is "operational" in the sense that it still works and will be used again, even though it is not "active" at the moment. The most recent and farthest-from-earth telescopic observations that ...

9

Freeform optics are a response to the specific challenge of cramming a telescope in a very limited space. A traditional instrument would have all optics symmetrical and aligned on the same axis. It would waste a lot of space within the cubesat. Also, traditional designs tend to be much longer than they are wider; they don't fit well in a cube; it is very ...

9

Convolution is not a uniquely invertible process in the presence of random noise in your image. Deconvolving a noisy image can give misleading results, even if you have perfect knowledge of the PSF. In general, when you are fitting models to data, it is far better to compare the models and data in the observational space of the data, where the uncertainties ...

9

Answering your subquestion about building on the moon: This is subject to the same launch costs and restrictions as a space-based 'scope, plus you have to deal with landing and with gravitational sag. So the first thing you need is a functioning moon base that can manufacture all components from local raw materials. Once that's in place (insert large ...

9

The gravitational focus you are talking about is actually a minimum value, defined by parallel rays of light from a very distant star just skimming past the Sun as they are bent according to General Relativity. The general formula for such lensing is that light is bent through an angle (in radians) of $$\alpha = \frac{4 GM}{c^2 r},$$ where $M$ is the mass ...

8

I'm not familiar with the design of the ProjectBlue telescope, but I think you have answered your own question. The habitable zones for Alpha Cen A and B, are approximately centred at 1.25au and 0.7au. Both are at a distance of 4.37 light years. 1au at 4.37 light years, subtends an angle of 0.74 arcseconds. If working at blue wavelengths (the aim appears ...

8

The James Webb Telescope is the next one on the launchpad that you might be familiar with. Although there are a few differences that one ought to be aware of. NASA has an entire program of telescopes to observe the universe, and many of them are designed for different wavelengths of light. The James Webb is primarily designed for the infrared part of the ...

8

This article contains a list of space telescopes. It's likely to be nearly complete. The extent of the Earth's atmosphere is not very well defined. The altitude at which Hubble orbits (about 550 kilometers above the surface) is above almost all of the atmosphere, but there's still enough residual air to cause some slight drag. It's not higher because it was ...

8

As the article you reference makes clear, the defocusing is deliberate. It spreads the light of bright stars (the main targets for CHEOPS) over more pixels and hence mitigates saturation and non-linearity problems in the detectors. The first light images look very similar to simulated pre-flight images (e.g. Hoyer et al. 2020; Futyan et al. 2020). The first ...

8

tl;dr they're a bit too small for SOHO and STEREO and only visible in EUV The "campfires" are described as a few hundred km across, The smallest of those campfires are about the size of a European country, according to Berghmans. which means that from Earth (or SOHO or STEREO) they will subtend from one to a few seconds of arc (a few micro-...

8

In addition to the target list linked to by @planetmaker in their answer, there are two recently published review articles (from Nature Astronomy) summarizing the many different aspects of Solar System science that were done with Spitzer: Lisse et al. (2020), "Spitzer's Solar System studies of comets, centaurs and Kuiper belt objects" Trilling et ...

7

The James Webb Telescope will not be orbiting around the Earth, but the Sun, at a distance of 1.5 million kilometers or 1 million miles from the Earth. A benefit to sending it further away from the Earth is that there's less of the interference of light pollution from the Earth. The JWST's mirror is 21 feet wide, though, so its sensitivity to this will be ...

7

It's very unlikely that large optical telescopes will ever be built on the Moon, because the Moon is almost the worst possible place to build them. (The surfaces any of the planets other than Earth are worse.) It has no particular advantages over orbit and costs a lot more to build there. The Moon looked like a good location when observatory technology ...

7

As the question Instrument aperture sizes on Hubble Telescope shows, the focal plane area is large enough to focus on several instruments at the same time (but with each capturing a different area). If two objects of interest are separated by a certain angle (the instruments are fixed within the focal plane), the telescope can be rotated so that two ...

7

Gravitational lensing works from anywhere beyond the focus, so in that sense, we could use any star as a gravitational lens. The problem is that the field of view is tiny. We only get any useful information from alpha centauri as a gravitational lens if the target object is almost exactly behind alpha centauri from our point of view. To look in a slightly ...

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More than 20 if the Wikipedia's List of Space Telescopes is accurate. I extracted the active ones, and removed duplicates (to the best of my knowledge): Swift Gamma Ray Burst Explorer AGILE FGST IKAROS NuSTAR Astrosat Insight (Chinese: 慧眼) Спектр-РГ (Spektr-RG) The famous Hubble Space Telescope, HST, see hst STSat-1 IRIS Hisaki Lunar-based ultraviolet ...

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One thing I always like to add is that ground based telescopes benefit from being able to take huge amounts of data. The Vera Rubin Observatory will have a 3.5 Gigapixel camera. There are proposals to sometimes run it in a mode with 1 second exposures. So we're talking data rates of gigabytes per second. If you have dedicated fiber lines you can deal with ...

6

The IRAS Point Source Catalog, Version 2.0, is a catalog of some 250,000 well-confirmed infrared point sources observed by the Infrared Astronomical Satellite (IRAS), i.e., sources with angular extents less than approximately 0.5, 0.5, 1.0, and 2.0 arcminutes in the in-scan direction at 12, 25, 60, and 100 microns (um), respectively. This includes some ...

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