Hi, im writing a project on ways to measure the angular size of our sun and distant stars.(adsbygoogle = window.adsbygoogle || []).push({});

I've been given a list of ways this can be done and have been told to research them. However im having trouble finding information on 2 of the methods.

Using the transit of planets: im assuming this can only be applied to our own sun as other planetary systems are difficult to find - only through variations in the intensity of light output from the star as the planet passes across it, this also has the problem of finding a system where the orbital plane lies perpendicular to the line to the observer.

So using the fact that planets in our own solar system (mercury and Venus) pass between the earth and the sun how can you use this to find the angular size of the sun?

Is it by again determining the variation of intesity output - this doesnt seem right to me, the size of the sun relative to the planet in this case is much too big and would be difficult to get an accurate reading.

Which leaves one method i think. Knowing the radius of the planets orbit, its angular size, distance to the earth etc, you can measure the time it takes to pass across the sun - therefore knowing the angular size of the sun. N.B ignoring that the orbits are circular etc.

Is this correct?

The second way:

Stefan's Law. This one i dont have many ideas for - the law itself

P = (sigma)AeT**4

Stars are black bodies = e = 1

I = P/A

So I = (sigma)T**4

Now we can find the intesity of light from a distant star. If we can find the distance to the star and assume that it is main-sequence, then we can anticipate the angular size of the star?

Thanks for any help, very much appreciated

Phil

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# The angular size of stars - prac astronomy

**Physics Forums | Science Articles, Homework Help, Discussion**