Re: Why do the legnths of day and nght change throughout the year?

Nicole, as you perhaps already know, we have different seasons because Earth is tilted with respect to its orbit. Mad Astronomer Phil Plait has an image showing this tilt on his Web site. When we're tilted closer to the Sun it's summer, and the Sun's apparent path over the sky is longer, therefore the time needed for Sun to move across the sky is larger. In winter, we tilt away from the Sun, the Sun's apparent path shortens and the Sun crosses the sky faster.

Interesting fact: Places far north (over polar circle at 66 degrees latitude) tilt so much from the Sun, that the Sun never completly rises in winter and on the other hand never setting in summer.

[It's worth pointing out that the northern hemisphere is tilted toward the Sun in June and July, but it closest to the Sun in December and January.]