What are the tropics of Cancer and Capricorn?
Think of the tropics of Cancer and Capricorn like the equator. On the Spring and Autumn Equinoxes (such as the one that just passed on March 20th) if you stand on the equator at noon the Sun will be directly overhead (at 90o). Here in Seattle the highest the Sun ever appears in the sky (at noon on the Summer Solstice) is 65o.
Because the Earth is tilted, on the solstices the Sun is further north or south in the sky than it is on the equinoxes. So, if you stand on the equator, the Sun is no longer directly overhead. On the Summer Solstice, if you stand on the Tropic of Cancer (the northern Tropic) the sun will be directly overhead. On the Winter Solstice, if you stand on the Tropic of Capricorn (the southern Tropic) the sun will be directly overhead.
Here are some pictures to illustrate this.
~ A l i c e !