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Historical evidence
supporting the existence of the concept
The concept of constellations can be traced back to as early as 4000
BC. The credit for the oldest known representation of constellations
goes to Sumer (now Iraq). Evidence that supports this has been found
in the form of motifs displayed on seals and vases among other
objects. All of us are familiar with the twelve signs of the zodiac.
These were known by the Babylonians around 450 BC.
The Greek poet Aratus of
Soli has mentioned descriptions of forty-four constellations in his
work Phaenomena. Ptolemy, an Alexandrian astronomer and
mathematician, described forty-eight constellations in his work
titled Almagest. Of the forty-eight described by him,
forty-seven are known today by the same name.
The constellations
recognized by the Greek and the Chinese were similar to the ones
recognized by Sumerians. In fact, the constellation recognized in
the Northern Hemisphere today are based on Greek constellations.
Zodiac Signs
One of the first sections a person is tempted to look for in a
newspaper is the daily forecast. Most of us do it, if not out of
belief then just out of idle curiosity. We check the forecast
assigned to our zodiac sign. And we decide upon our zodiac sign on
the basis of the dates given under each sign.
Ancient astronomers
noted that the sun makes a yearly journey across the celestial
sphere. The twelve constellations referred to as the signs of the
zodiac were identified on this basis. And different times of the
year were assigned to them, on the basis of the sun being in the
same region as the identified constellation at the same time.
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Ptolemy, an astronomer
from the second century, named the twelve zodiac signs. The twelve
constellations with their English names are:
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Aries – Ram
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Taurus – Bull
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Gemini – Twins
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Cancer – Crab
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Leo – Lion
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Virgo – Virgin
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Libra – Balance
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Sagittarius – Archer
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Capricorn – Goat
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Aquarius – Water Bearer
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Pisces – Fishes
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Some other
interesting names
A few other well known constellations have interesting names based
on names of animals and birds. They are: Cetus – whale, corvu –
crow, equuleus – little horse, Ursa Major – Great Bear, Canis Minor
– Lesser dog.
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Johann Bayer, a 17th
century German astronomer introduced a system wherein the name of a
constellation is preceded by a Greek letter. One thousand three
hundred stars have been named as per this system. For example, Beta
Persei is the name given to a star Algol in the constellation
Perseus.
Scientific basis of
constellations
The matter of definite boundaries of each constellation was a
matter of speculation. The situation was however remedied by the
International Astronomical Union in 1930, by fixing definitive
boundaries in such a way that constellations do not overlap each
other. To aid them in this, astronomers use a system akin to the
latitude and longitude system in geography. Coordinates are used to
pinpoint the location of objects in the sky. The altazimuth system
and the equatorial system are the widely used coordinate systems.
The concept of a celestial sphere – an imaginary globe surrounding
the earth – is used to help in fixing of coordinates. One of the
main uses of constellations is for tracking artificial satellites
and assisting in the location of specific stars. |
