00:01
In question number nine, we're asked to compare the apparent brightness of the sun from jupiter with the apparent brightness of the sun from earth.
00:09
The formula for the apparent brightness of a star, little l, is equal to big l, luminosity, divided by four times pi times d squared, where d is the distance away from the star, from which we're measuring its brightness.
00:28
And the problem, we're given that jupiter's distance from the sun, i'm going to call that d sub j, that's equal to 5 .2 times earth's distance from the sun, which i'm going to call d sub e.
00:43
Now, we could plug in the value for the sun's luminosity and the value for earth's distance and multiply it by 5 .2 to get jupiter's distance from the sun.
00:55
But let's make things simpler and just go with using as few numbers as possible to work this out.
01:03
So the apparent brightness from earth is going to be equal to big l divided by 4 times pi times d sub e squared.
01:15
And then the apparent brightness from jupiter is going to be equal to big l over 4 times pi x x squared.
01:28
We can substitute for d sub j by replacing it with 5 .2 d sub e...