The Space SE question JWST detector heat load asks

...what is the heat load from the collected radiation of the main mirrors on the detector, and how does that vary depending on what objects or fields are being imaged?

and that might be addressed by considering the brightest point source and the brightest extended region integrated over a given detector's field of view. It would not be a trivial question to answer without doing a lot of checking.

To that end, and potentially to help answer authors there, I'd like to get an idea of the following:

Question: What does the celestial sphere look like in thermal IR?

There may be surveys at say 10 or 20 or 30 microns from previous IR space telescopes or even at certain wavelengths from the ground. I'm guessing that besides the Sun and Moon there are not a lot of bright stars nor planets, except for Venus and perhaps Mercury, and that dust in the galactic plane will dominate, but I could of course be way off!

I don't want to specify this question so narrowly that a good answer can't be posted, so I will leave this particular one a bit broad to allow for helpful and informative answers.

update: On the question of wavelength; I'm pretty flexible here. If I were to specify 1 - 30 um and it then turns out there's a beautiful survey at 31 - 42 um but it never gets mentioned, that would be sad.

  • 1
    $\begingroup$ 9 µm: esa.int/Science_Exploration/Space_Science/… $\endgroup$ Feb 3, 2022 at 8:43
  • 2
    $\begingroup$ Also the WISE all-sky map at 3.4, 12 and 22 $\mu$m $\endgroup$ Feb 3, 2022 at 17:49
  • $\begingroup$ Not from space, but the ground. I recently built a cloud detector using a low resolution IR sensor. The only astronomical object that shows up is the Sun (not sure if I tested the moon). This thread has some photos. cloudynights.com/topic/… $\endgroup$ Mar 11, 2022 at 16:46
  • $\begingroup$ I think you might need to be a little more specific about what you think "thermal IR" entails. How much shorter than 10 microns is allowed? How much longer than 30 microns? E.g., this link defines "thermal IR" as basically 1-15 microns... $\endgroup$ Mar 11, 2022 at 17:15
  • 1
    $\begingroup$ @uhoh Well, most astronomers would consider “100 microns” as far-infrared, not radio; the transition is more in the vague region of 300 microns (e.g. “sub-mm” radio telescopes like JCMT and ALMA tend to start at $\sim 400$ microns). But you update helps. $\endgroup$ Mar 12, 2022 at 10:33

1 Answer 1


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, so the disk of the Milky Way defines the "equator".

For the shorter wavelengths, I'm using observations from the Diffuse Infrared Background Experiment (DIRBE) instrument of the COBE satellite. [Source] The first images are for the shortest wavelengths (shorter than "thermal IR"): 1.25, 2.2, and 3.5 microns. These are dominated by emission from stars in the Milky Way, though you can see zodiacal light concentrated near the ecliptic plane -- this is the backwards-S-shaped curve of diffuse emission. For 1.25 and 2.2 microns, this is sunlight scattered by dust grains in the inner Solar System; at 3.5 microns, there's an equal contribution from actual thermal emission from the dust grains.

enter image description here

The second figure shows longer-wavelength maps from DIRBE: 4.9, 12, 25, and 60 microns. Here, you can see the growing dominance of thermal zodiacal dust emission, which is strongest in the 12 and 25 microns wavebands. At 4.9 microns, the Galactic emission is still mostly from stars, though there is a contribution from hot interstellar dust. At longer wavelengths, the Galactic emission is thermal mission from the interstellar dust; and in fact this dominates over the zodiacal emission in the 60 micron waveband. (This is because the Galactic dust is generally cooler than the zodiacal dust.)

enter image description here

For even longer wavelengths, I'll turn to maps from the AKARI satellite: 65, 90, 140, and 160 microns (out to the approximate limits of what is traditionally considered "far-IR"). [Source] You can see that thermal emission from the zodiacal dust is still present at 65 and 90 microns, though it's mostly gone from the longer wavelengths. Galactic dust emission is the dominant source in all the AKARI wavebands.

enter image description here


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .