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It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert,
by joshvm 5y ago
It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight. At the South Pole on a clear night we would walk out to the dark sector (where the telescopes are) with our headlamps off because it just wasn't necessary. The only illumination sources outside were red safety lights[1] and we'd normally turn those off for long exposure photography. You do need a fast lens though, and that inevitably means lots of glass.
Whether the telescope is reflective enough to get a good photo is another matter - I would guess not, it's designed to minimise stray light.
As for IR, the telescope is probably bright compared to the background at least for now. The main issue though is whether you'd need to actively cool the engineering camera. Cooling stuff in space is difficult because you can only really dump heat via radiation. It's probably not worth the weight to carry a separate cryocooler just for that. The inability to conduct heat is partly why it takes so long to cool down, aside from minimising thermal stress on the infrastructure.
[1] The main reason they exist is so that you have a point of reference when walking about outside, particularly on foggy or cloud days. The meteo folks also use them as visibility markers in winter - e.g. IceCube is something like 1km from the station by line-of-sight. Turning them off for a brief period is usually fine and we'd notify the station before we did it. On a clear night though you don't need them at all.
- JohnBooty 5y agoIf you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight This reminds me... I need to experience this firsthand at some point. Thank you! Question: how much (if any) of that light is due to atmospheric scattering? ie, the sun's light hitting the daytime side of the earth, being scattered in our atmosphere, and faintly illuminating the night side of our planet? Would the same be true in the zero-atmosphere environment of space? Here are some possible answers: https://space.stackexchange.com/questions/25901/how-bright-is-starlight-in-deep-space https://space.stackexchange.com/questions/25901/how-bright-i...
- joshvm 5y agoPlenty of places around the world offer dark enough conditions (but make sure it’s a new moon) - in the US you just need to get out to Arizona or Joshua Tree (or similar empty places). In Europe and elsewhere look for International Dark Sky Reserves. In general go visit places where telescopes are built. Possible that some of it is from scattering and then if course you wouldn't get that in space as there's no atmosphere to scatter from! Scattering is incredibly faint though, even compared to starlight. See also gegenschein and the Zodiacal light - both are backscatter effects.
- joshvm 5y agoSlight addendum - actually you often want satellites to be reflective. Dark means good radiator, but also good absorber and a black spacecraft is about as bad as you can get for thermal management if you point it in the wrong direction. For an Earth orbiting craft that means it’ll overheat in sunlight and then dump everything in shadow - lots of thermal stress and not good for instruments that like a constant temperature. That’s why you often see sats covered in polymide foil.