(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

This is the questions:

1) The angular diameter of the sun measured from the earth is 0.52 degrees. Calculate:

i) the angular diameter in radians

ii) the sun's radius in meters

iii) The surface area of the sun, assuming that it is a sphere

2) Using L=aAT4 where L is the luminosity, a is the stefan-Boltzmann constant: 5.67X10^-8, A is the surface area, T is the temperature.

Calculate the total power and the power per m^2 radiated by the earth at a temperature of 228K. You can assume that the earth is a sphere of radius 6400km.

3. The attempt at a solution

Question 1:

Question i) is quite easy and found out that it is 0.00908

Question ii) is the major problem. I tried to assume that it is a triangle and used the sine rule (since i know the distance of the sun to the earth is 149X10^11m while the other angles in the triangle should be (180-0.52)/2. However, this gave me an answer of 1.4X10^9. If i divide by 2 (to find the radius), i ger 7X10^8m.

The answer at the back of the book is 1.4X10^9m. which is double my answer. I suspect that the book may be wrong but just wish to double check

Question iii) if i knew the answer to question ii), i would be able to do this.

Question 2: I thought that this question should be easy where i just put in the numbers into the equation... but i couldn't get the right answer...

L=aAT^4

L = (5.67X10^-8)*(4*pi*6400000^2)*(228^4)

L = 7.89X10^16

The book's answer is 201X10^15 W

Thank you very much

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

Dismiss Notice

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!

# Homework Help: Angular diameter

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