Question

On any given day, why does the photoperiod vary throughout the world?

I have no idea about what they're asking? :S

Answer 1

Start with these definitions of photoperiod.

http://www.google.com/search?hl=en&defl=en&q=define:Photoperiod&sa=X&ei=HGdYTeDBA8m4tweFqqzMDA&sqi=2&ved=0CBMQkAE

Then think about the rotation of the earth.

Answer 2

Is it because when one part of the earth is facing the sun they go throught daylight and other side go through darkness?
I'm totally not understanding this.

Answer 3

The sun reaches its northernmost point over the Tropic of Cancer in June. At that time, the north Polar regions receive 24 hours of daylight and the south Polar regions receive 24 hours of darkness.