Cancer, a constellation and the fourth sign of the zodiac. Cancer is the Latin name for crab; presumably, the unknown person who named it thought the constellation resembled that animal in shape. The Tropic of Cancer, an imaginary line 23 27' north of the Equator, marks the northernmost points reached by the sun's vertical rays. It is so named because in ancient times the sun was highest in the northern sky when it was in the same area of the sky as Cancer.
Our knowledge of space changes all the time as new discoveries are made. But some ideas about the universe have never really held water – including the one that everything is made of frozen H2O.
A look at the night sky at any time of year will reveal a faint band of light stretching across the sky -- our solar system's home, the Milky Way. How much do we really know about it?