# What 'area' is the sky of the earth?

• April 2nd, 2012, 06:08 PM
Quantime
What 'area' is the sky of the earth?
What is the total 'area' of the sky we can see from earth? Not sure how to phrase this but what would be the value of space that the sky equals, if say the moon was 1cm in diameter? (using that as just an example to try to explain what I mean)

Say for instance at one point on earth as far as the horizon all around (assuming the earth has no hills or dips), what would be the area of space out of all space visible across the sky that one could see.

Then what is then the total 'area' of the sky we can see? I wanted to then be able to map exactly what percentage of the sky around the earth that the moon covers at average distance.

Not sure if I made that seem clear?
• April 2nd, 2012, 06:23 PM
mathman
I think it would be much clearer if you looked at in terms of solid angle rather than area. The sky that is visible is about 1/2 the total, so the solid angle would be 2π steradians. The moon solid angle is 6.4236x10^-5 steradians (I got this from the second reference).

Solid angle - Wikipedia, the free encyclopedia

Lunar Calibration - Lunar Irradiance Model