Question

why is the equator hotter than the north and south poles?

Answer 1

Because the amount of light striking a unit area is greater at the equator than at either pole.

The following might help.

Take a ruled piece of paper and pretend the lines represent rays of light coming from the sun. Now take another piece of paper and lie is verticially on that one, such that the lines on the two pages line up. Note that each line-to-line interval in the second sheet receives exactly one line-to-line interval on the first sheet. That is analogous to the equator.

Now, hold the second sheet near its last line and start rotating it clockwise, until it has been rotated about 45 degrees. Now note that each line-to-line interval on the second is matched up with LESS than 1 line-to-line interval the first. Thus, less rays of sunlight are striking each unit area when the surface it tilted away from being perpendicular to the light source.

As you rotate it more and more, each unit on the rotating sheets receives less and less line-intervals (light rays). This models near the poles.

Answer 2

The sun appears overhead near the equator -- from 23.5 degrees North to 23.5 degrees South. The farther from the Equator the farther the sun's rays have to travel.

http://geography.about.com/library/misc/blequator.htm