20 votes

Which (if any) space telescope would have worked longer if it hadn't simply run out of helium?

Past infrared telescopes (IRAS, Spitzer, others I can't remember) in space have generally used expendable liquid He. They either ceased operation or lost a large part of their capability when the He ...
John Doty's user avatar
  • 1,876
18 votes

Which (if any) space telescope would have worked longer if it hadn't simply run out of helium?

The Herschel infrared telescope is another recent telescope that stopped working once it ran out of Helium for its coolant.
Rob's user avatar
  • 2,035
16 votes

Why is detecting brown dwarfs difficult?

Brown dwarfs have historically been difficult to detect (directly) simply because of how faint they are. Typical luminosities may range from $10^{-3}L_{\odot}$ to $10^{-5}L_{\odot}$ depending on ...
HDE 226868's user avatar
  • 36.6k
13 votes
Accepted

Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?

There's a pretty good discussion at this page. There are several factors at work: The smaller isoplanatic angle, as you note. This limits how much of the sky you can observe with AO, since your ...
Peter Erwin's user avatar
  • 16.7k
12 votes
Accepted

Was GRAVITY built to look at one star?

No, the GRAVITY instrument is multi-purpose. This link gives you all the papers that have cited the instrument description paper. The list of papers shows that it has been used for studying: the ...
ProfRob's user avatar
  • 152k
10 votes
Accepted

Question: By design, JWST cannot observe in the anti-sun direction. Is this due to Gegenschein backscatter?

I'm going to say no. Gegenschein is, as you note, reflected sunlight, and is the brightest part of the (reflected component of the) zodiacal light. It's not very bright in the optical (there are no ...
Peter Erwin's user avatar
  • 16.7k
9 votes
Accepted

Why was helium hydride (HeH+) the universe's first molecule?

At the risk of self-plagiarism: (https://physics.stackexchange.com/a/532568/43351 with a bit added). Molecular chemistry in the early universe requires species with bound electrons. Helium hydride is ...
ProfRob's user avatar
  • 152k
9 votes
Accepted

Did they ever figure out why Parker's WISPR cameras were able to see the surface of Venus? Mischaracterized filter, or unexpected atmospheric window?

There's actually a paper by Wood et al. (2022) that came out focused on this. It discusses the expected detection given the expected emission (using a model that combines the surface emission and the ...
Peter Erwin's user avatar
  • 16.7k
9 votes

Acetylene at Uranus? What's JWST's evidence and current thinking of how it's possible?

I think part of the issue here is that you seem surprised to learn that JWST detected acetylene in the atmosphere of Uranus, as though this is both unexpected and merits a certain amount of skepticism ...
Peter Erwin's user avatar
  • 16.7k
6 votes
Accepted

Is there an IRAM satellite that measures thermal radiation at 250 GHz, or was this a ground-based instrument?

The Nature paper by Bertoldi et al. (2006) says: Our millimetre observations were performed with the Max-Planck Millimeter Bolometer (MAMBO-2) array detector at the IRAM 30 m telescope on Pico Veleta,...
astrosnapper's user avatar
  • 8,357
6 votes

What are IRAS sources?

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 ...
Rory Alsop's user avatar
  • 5,063
6 votes

Is it possible for a planet to heat up its moon to habitable temperatures solely through infrared radiation?

Consider a planet with effective temperature $T$ radiating as a blackbody, emitting a total luminosity $L=4 \pi \sigma R^2 T^4$. At distance $a$ the power per square meter will be $$P = \frac{L}{4\pi ...
Anders Sandberg's user avatar
6 votes
Accepted

What is the infrared self-luminosity value of Jupiter and Saturn?

According to Li et al. (2018), the internal heat coming from Jupiter (and emerging almost entirely as infrared radiation) is $7.485 \pm 0.160$ W/m$^2$. If we take an average radius for Jupiter of 70,...
ProfRob's user avatar
  • 152k
6 votes

Acetylene at Uranus? What's JWST's evidence and current thinking of how it's possible?

A compilation of the known compositions of the gas giant planets (by number density), compiled from several sources indicated in the table, is given Lodders 1. References cited in the table [2-6] are ...
Oscar Lanzi's user avatar
  • 1,113
5 votes
Accepted

Why is the "green" comet C/2014 Q2 (Lovejoy) red in this picture?

Mainzer et al. 2014 characterize the performance of the reactivated NEOWISE. Having run out of cryogenic coolant for the original WISE's 12 and 22 μm bands, it only detects in the 3.4 and 4.6 μm ...
Mike G's user avatar
  • 18.7k
5 votes
Accepted

What exactly is the risk to any JWST instrumentation when looking at objects that are "too bright"?

The MIRI uses Si:As doped detectors which I believe are just about destruction-proof. The spectral dispersion is done with Ge and ZnS material, also tough things. There's a wealth of info on the ...
Carl Witthoft's user avatar
5 votes

What are the bright dots in some galaxies in the first JWST image?

Myung Gyoon Lee et al 2022 seem confident that they are globular clusters. Faisst et al 2022 seem to also consider the possibility that they could be stripped cores of dwarf galaxies. They are both ...
Prallax's user avatar
  • 4,431
5 votes

Narrowband imaging wavelengths in NIR?

The main problem with NIR is that the atmosphere quickly becomes opaque for various bands inside the range due to the absorption bands of water vapour. E.g. see a lecture document on spectral ...
planetmaker's user avatar
  • 19.4k
5 votes
Accepted

Narrowband imaging wavelengths in NIR?

Yes, there are some obvious nebular emission lines in this range - the whole of the Paschen series (transitions in hydrogen atoms to the $n=3$ level) lie between Paschen alpha at 1875 nm to the ...
ProfRob's user avatar
  • 152k
4 votes

Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?

The simple answer for the wavelength part is that performance of AO systems degrades the shorter in wavelength you look. The basics of what happens is as you go to shorter the wavelengths of light, ...
veda905's user avatar
  • 225
4 votes
Accepted

Can the WISE telescope detect black holes?

Black holes are black. They are only observed directly by telescopes if they are accreting matter. Any radiation observed comes from the matter surrounding the black hole. Generally speaking, the ...
ProfRob's user avatar
  • 152k
4 votes

How much infrared radiation is emitted by a bow shock?

Has the amount of energy being emitted from R Hydrae's bow shock been studied? Yes, here are a few papers: "Detection of a Far-Infrared Bow-Shock Nebula Around R Hya: the First MIRIAD Results" (July ...
Rob's user avatar
  • 2,646
4 votes
Accepted

What's that limit, where we start to see infrared galaxies?

Galaxies give off a range of frequencies of light: Visible, but also infrared, microwave, and radiowaves. at longer wavelengths, ultraviolet, Xrays and gamma rays at short wavelengths. But stars give ...
James K's user avatar
  • 122k
4 votes

Number of lenslets in wavefront sensor array

Generally speaking as many as possible because the number of lenslets determines the lateral wavefront resolution. But in reality there are a few factors to be considered. Wavefront sensor Say your ...
WDC's user avatar
  • 454
4 votes

Is it possible for a planet to heat up its moon to habitable temperatures solely through infrared radiation?

Partial problem with Anders' answer: 730K is a "hot Jupiter", which I think are usually kept hot by stellar insolation, which would also heat the proposed moon. Removing that heat-source: ...
user19177's user avatar
4 votes
Accepted

What does the celestial sphere look like in thermal IR?

Let me see if I can provide some examples of the general background (not including small-angular-size sources like planets and individual stars). These are all-sky projections in Galactic coordinates, ...
Peter Erwin's user avatar
  • 16.7k
4 votes
Accepted

Why is infrared the ideal band to detect the earliest and most-redshifted galaxies?

Large stars emit much of the there energy in the visible and near-ultraviolet wavelengths, but a galaxy at z=10 will be observed most brightly in the infra-red. Moreover, lots of the interesting ...
James K's user avatar
  • 122k
4 votes

What is the infrared self-luminosity value of Jupiter and Saturn?

The luminosity of an object is proportional to the square of its radius and the fourth power of its temperature, Jupiter has radius of 0.1 solar radii and a temperature of 160 or 0.0285 of the sun. So ...
James K's user avatar
  • 122k
3 votes

First Confirmed Visual Observation of Gravitational Lensing

The first identified gravitationally lensed object is known as the Twin Quasar. The Twin Quasar (also known as Twin QSO, Double Quasar, SBS 0957+561, TXS 0957+561, Q0957+561 or QSO 0957+561 A/B), was ...
PM 2Ring's user avatar
  • 14.5k
3 votes

What determines the surface material of the ALMA and Spitzer telescope?

They're all mirrors, they just operate in different wavelength ranges. A wire fence could be a mirror if the wavelength is big enough. The surface is an easy problem to solve. Pick any material and ...
Florin Andrei's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible