00:01
In this problem, we have this star betelgeuse somewhere here, and we know its angular diameter as measured from earth.
00:13
So we have this geometry essentially.
00:18
This is the angular diameter and it is given to be 0 .040 arc seconds.
00:29
And we know the distance from earth to this star.
00:35
Let's call it lowercase d.
00:37
It is 720 light years.
00:41
So the question is, what is the actual diameter of this star? let's call it capital d.
00:50
Since this distance is much larger than the size of the star, we can use this approximation to relate all these three parameters.
01:06
Capital t is approximately equal to d times theta d.
01:11
So we have 0 .040 arc seconds times 720 light years...