I did some calculations on that moon from the comic. This was just some quick and dirty math, so if I messed up or fudged the numbers too much, feel free to double check.
Anyway, the size of the moon in that picture is somewhat dependant on its height off of the ground. The real-world troposphere is about 17 km, which I used as the absolute maximum. However, I used a distance of about 100 m for the minimum, since clouds in Equestria are generally much closer to the ground. I also used a distance of 2 km as a medium between the two extremes.
If the moon is 17 km off the ground, then by my calculations it has a radius of 127.5 km, a surface area of 204, 282 sq. km and a volume of 8, 681, 988 cu. km.
If the moon is 100 m off the ground, then it has a radius of .75 km, a surface area of 7.1 sq. km and a volume of 1.77 cu. km.
If the moon is 2 km off the ground, then its radius is 15 km, its surface area is 2, 827 sq. km and its volume is 14, 137 cu. km.
For comparison, our moon's radius is 1, 737 km, its surface area is 37, 930, 000 sq. km and its volume is 21, 958, 000, 000 cu. km.
edited 4th Apr '13 8:54:48 PM by IrishZombie
Oh, no! They've all transformed into giant, Swedish, lederhosen-clad yodelers! Run!