Gloria LeVine, age 11, of Tucson, Ariz. for her question:
How did the Tropic of Cancer get its name?
The Tropic of Cancer is a line parallel to the lines of latitude which run clear around the globe. It is near latitude 23 degrees north of the equator. The Tropic of Capricorn is near latitude 23 degrees south of the equator. The wide belt between these two circles is called the tropics. Strange to say, both the Tropic of Cancer and the Tropic of Capricorn are named for constellations of the zodiac.
The zodiac is a huge, heavenly circle of 12 constellations which come and go with the seasons, We always see the sun against a background of one of these 12 starry constellations. Also, throughout the year, the sun seems to travel a path which takes it north and south of the equator. At the equator, the noon sun is overhead, The noon sun is lower in the sky as we travel north or south of the equator. When we have summer, this path takes the sun north of the equator. When we have winter, the suns path takes it south of the equator, And each month of the year takes the sun through one of the constellations of the zodiac.
When the South Americans and the Australians are having summer, we are having winter. For us the noon sun is low in the sky. In the southern hemisphere, it is overhead a little south of the equator. For us, each day gets shorter, for them each day gets longer until December 22. This is the day of the winter solstice when the sun reaches the limit of its journey into the southern hemisphere.
For the southern hemisphere, this is the longest day of the year and the noon sun is overhead as far south as the Tropic of Capricorn. At this time of year, the sun is in the zodiac constellation Capricorn the Goat.
The Tropic of Capricorn is the point where the noon sun is overhead on the longest day of the year south of the equator:
Right after the winter solstice, the sun begins its journey north. The noon sun creeps higher in the sky north of the equator. It is no longer overhead at the Tropic of Capricorn. South of the equator, each day gets a little shorter. North of the equator, each day gets a little longer and the noon sun is overhead further and further north from the equator until June 22.
This is the day of the summer solstice. The sun reaches the limit of its journey into the northern hemisphere. We have the longest day of the year and the noon sun is overhead at the Tropic of Cancer. At this time of year, the sun is in the zodiac constellation Cancer, the Crab, The Tropic of Cancer is the point where the noon sun is overhead on the longest day of the year north of the equator.