00:01
All right, so let's say the star alpha centauri has an apparent brightness or an intensity, we'll say, of 2 .7 times 10 to the negative 8 watts per square meter as viewed from earth.
00:14
And it is a distance, we'll call this r, of 4 .4 light years away.
00:21
So we want to know how intrinsically bright it is in terms of the power output.
00:26
So first let's convert 4 .4 light years to meters.
00:31
This should be 9 .45 times 10 to the 15th meters per light year.
00:38
And so if we do that, this should be 4 .158 times 10 to the 16th meters.
00:50
And so the power output, sometimes called the luminosity of a star, is going to be the intensity that we receive on earth times four.
00:58
Pi little r squared so 2 .7 times 10 to the negative 8 watts per square meter times 4 pi times 4 .158 times 10 to the 16 meters squared and so if we multiply all those numbers together we get a power output that is somewhat comparable to the suns it's about 5 .8 we'll say 7 times 10 to the 26 watts.
01:32
The sun's power put is like 3 .89 or something...