Cancer is a constellation known as the Crab. It is a constellation of the Northern Hemisphere. Cancer lies between the constellations Gemini and Leo in the night sky. It is best viewed from around January through April. Cancer was among the 48 constellations defined by the ancient Greek mathematician Ptolemy. Today, it is one of 88 constellations recognized by the International Astronomical Union, the leading authority in the naming of heavenly objects. Cancer is also one of the 12 signs of the zodiac used in astrology (see Cancer ).
Cancer is commonly shown to include about five stars. The constellation can be drawn as three lines radiating from a central star to three nearby stars. One of these lines passes through another star.
The stars in Cancer are all dim compared to the brightest stars in the sky. Cancer is thus not usually visible around most cities due to light pollution. Light pollution is a brightening of the night sky caused by an abundance of artificial lighting.
