Night and day

Night and day

. The Earth rotates with respect to the Sun once every 24 hours, causing the sequence of night and day. Each point on the Earth’s surface moves in a circular track parallel to the equator, and each track spends a different time in the Sun depending on the season. This drawing depicts summer in the Northern Hemisphere and winter in the Southern Hemisphere. Because the northern part of the Earth’s rotational axis is tipped toward the Sun, circular tracks in the Northern Hemisphere spend a longer time in the Sun than southern ones.

Copyright 2010, Professor Kenneth R. Lang, Tufts University