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Definition
The popular definition of a constellation is a group of stars that form a pattern when seen from Earth. However, for astronomers, all stars are part of a constellation. Astronomers draw boundaries around each constellation. The edges of these boundaries touch, dividing the sky into separate constellation regions. All stars within a constellation's boundary are part of that constellation, even if they are not part of the star pattern.
Seasonal Changes
Constellations appear to gradually shift to the west as the Earth orbits around the sun. During the summer, stargazers are looking in a different region of space than they are during the winter.
Nightly Changes
The constellations also appear to move from east to west across the sky each night. This apparent movement occurs because the Earth spins on its axis. Polaris, also called the North Star, appears to move little in the night sky because it is almost directly above the Earth's North Pole.
How Many Constellations
In 1930, the International Astronomical Union officially recognized 88 constellations throughout the entire sky. These include representations of 29 inanimate objects, 19 land animals, 14 men and women, 10 water creatures, nine birds, two insects, two centaurs, and one head of hair, serpent, dragon, flying horse and river. These numbers add up to more than 88 because some constellations include more than one item.
History of Constellations
Of the 88 recognized constellations, 50 date back to ancient Middle Eastern, Greek and Roman cultures. These are the brightest constellations and can be seen with the naked eye. Astronomers using telescopes identified 38 additional constellations in the 16th through18th centuries. These modern constellations include a peacock, a giraffe and a telescope.