Question

The apparent angular size of the moon is about 1/2 degree, how many full moons could fit across the apparent size of the Andromeda galaxy?

Answer 1

About `6`

Explanation:

The Andromeda galaxy is about `2.5` million light years distance from us and has a diameter of approximately `140000` light years.

So it subtends approximately:

`(1.4*10^5)/(2.5*10^6) = 0.056` radians

In degrees, that's:

`0.056 * 180/pi ~~ 3.2^@`

So about `6` times the angle which the full moon subtends.

That having been said, we only usually observe the bright central area of the Andromeda galaxy by naked eye or small telescope under normal conditions, so it appears much smaller than it actually is.