1. The radius of the Sun is 7 X 10^5 kilometers. Use powers of ten to show that the Sun's radius is about 100 times the Earth's radius.

2. Given that an astronomical unit is 1.5 X 10^8 kilometers and a light-year is about 10^13 kilometers, how many AU are in a light-year?

1 x 10^13
----------
1.5 x 10^8

equals

.667 X 10^5 or 6.67 X 10^4
More exact is 63,239.4913

So if the earth is 6.4 X 10^3 radius
and the sun is 7 X 10^5 just take 6.4 X 10^3 times 109 to get 7 X 10^5
Means the sun is 109 times bigger than earth.