Constellation
A constellation is the pattern formed by the stars in a particular region of the sky, with boundaries that are officially defined. The sky is divided into 88 constellations, and this division is the address system of star maps.
| In brief | A constellation is a region of the sky whose boundaries are officially defined, and the pattern formed by the stars within that region. |
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| Astronomical account | The sky is divided into 88 constellations by the boundaries fixed by the International Astronomical Union in the 1920s. The members of a constellation are not a physical group; they are visual patterns formed along our line of sight by stars at different distances, and in modern usage a constellation denotes a region of the sky. |
| Use in astrology | Astrology uses the ancient constellation names of the zodiac belt as the names of the signs; the interpretation, however, rests not on the constellation itself but on the equally divided slices of the ecliptic. In this sense the constellations have left astrology a legacy of names and symbols. |
| Evidence status | Constellation boundaries and the measured distances of the stars are verified data of observational astronomy. There is no scientific evidence for a relationship between star patterns and human character or destiny; that link belongs to the domain of cultural narrative. |
| Common misconceptions |
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The pattern is ours, the stars are independent
The stars of a constellation are most often unrelated to one another physically: some are hundreds and some thousands of light years away, and they appear side by side only from our point of view. It is human culture that sees the patterns and names them; different civilisations have drawn different shapes from the same stars. Today's list of 88 constellations, with its exact boundaries, was standardised by the International Astronomical Union in the 1920s.
The constellation as an address system
In modern astronomy a constellation is a region rather than a shape: every point in the sky falls within the boundaries of exactly one constellation. The sentence "a new comet is in the constellation Hercules" says not that the object is related to the stars of Hercules but that it appears in that region of the sky. This is a mapping practice much like the boundaries of a city.
Their relationship with the signs
The 13 constellations that cross the zodiac belt gave their names to the 12 signs of astrology; but while the signs are equal slices, the constellation boundaries are not equal, and precession has shifted the two systems apart over time. For the detail you can look at the Zodiac record.
Related terms: Zodiac, The Ecliptic, Precession