Expert: Jayendra Upadhye - 11/25/2008

Question
We know when we seee means light falls on an object and it enters in our eyes, that is what we "see". This phenomenon require medium. My question is that in the absence of medium in space ( outside  orbit of earth ) can we see sun or  other planets or stars what we can see from earth. If yes why and what will be temperature in space since we will be comparatively nearer to sun.

Answer
Hi Abhay,
I would like to know your age.
If you are young, i can understand.
if you are older, i will just say you are courageous and need to be complemented for not shying away in showing you "dont know" certain things.

Well, all of space in the vicinity of the earth's orbit (93 million miles from the sun), is uniformly irradiated by the sun at 1.4 kilowatt per square meter!

This is known as the solar constant.

By going into orbit around the earth, we are not really neaere or farther from the sun! What is a few 100 or 1000 miles in a distance of 93 million miles?

Even the moon gets more or less same dose of solar radiation. Even though it orbits us a 400,000 km distance!

Regarding "temperature" of space...it all depends on how much of the radiant solar energy one absorbs and how much we radiate away. (this is called Albedo). In space when exposed continually to solar radiation, and with no atmosphere for convective heat loss, things heat up till newtons law of cooling makes the radiative heat loss same as radiative heat gain. This stable temmperature is different for different things, depending on their color, texture, radiative efficiency.

Other wise in solar shadow, anywhere in space, things quickly cool to the "temperature of space", which is the temperature of the cosmic background radiation. (about 3 deg kelvin). Nothing can be cooler than that. The universe is at this temperature after cooling off from the time of the big bang. Period.

The solar constant itself will fall off as an inverse square of distance. The constant of that proportionality you can find if you know 2 values of the constant at differing distances.
(And know how to solve simultanous equations / matrices).

As to seeing, well we continue to see as we 'see' on earth! Except, intervening space between bright objects appears pitch black. As there is no medium to disperse light, and so there is no glare too.

regards
Jayen