A question was posed that I decided to have a crack at, and I want to check my understanding. This isn't homework by the way, just trivia. Also the thread title is not really correct but I didn't want to complicate things! Here's the question: What is the relative difference in the distance from the sun of two points on the earth. Specifically Montreal, Canada and Melbourne, Australia. I started by finding out their respective latitudes. With these in hand, I drew a circle and some interior right triangles and set about finding the horizontal distance component from the equator to the point on the circle. I'm pretty sure I have these correct, here is my data so far: Radius of Earth: 6378.1km Montreal: -Latitude: 45.5081° N -Horizontal distance from equator: 1908.3km Melbourne: -Latitude: 37.7833° S -Horizontal distance from equator: 1337.3km Now, I need to account for the axial tilt of the earth, which is 23°. Given that it's the middle of summer/winter, the difference in distance from the sun will be at a maximum. What I did was to get the horizontal distance component for a point (the equator) at 23° latitude, which is 507km, and +/- from my above results, and I get a relative difference in distance of 1585km between the two cities. Anyone care to comment or correct my reasoning? :) Also, what is a good resource for astronomical measurements? I'd like to turn this into a program but I need to know about the elliptical orbit of the earth.