Ask A Scientist Astronomy Archive

name         Fernando
status       student
grade        K-3
location     NY

Question -   Why do the north pole and the south pole have 6 months of 
daylight and 6 months of darkness?  How can there be only one sunrise and 
sunset each year, not day?  I heard that on the first day of fall, there 
are twelve hours of daylight and 12 hours of night.  Please help.
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Fernando,

Try this: You need a ball, a marker pen, a flashlight and a reasonably 
dark room. Mark a spot on the ball with the letter "N". On the opposite 
side of that mark, mark the ball with the letter "S". Then, in the middle 
(between the two marks) draw a line around the whole middle section. Now 
bring the ball to a dark room and shine the flashlight on the ball such 
that the light is hitting directly on the middle line that you drew. If 
you did this just right, then the N and S will be at the top and barely 
getting light. As the ball rotates you can will see that that gives the 
night/day or sunrise/sunset for the middle line. but notice how, as you 
rotate the ball, the N and S spots always receive some light from the 
flashlight?

So if the Earth did not have a tilted axis, then the north (N) and south 
(S) poles will always get sunlight. But with a slight tilt, these spots 
will get either get a lot of sunlight or none depending on the direction 
of the tilt. Thus, as the tilt axis changes, the days can be very long or 
the nights can be very long.

Greg (Roberto Gregorius)
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