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Stars in your eyes

The Zodiac Signs - Astronomy and Astrologypainting of Ptolemy

A constellation is a groups of stars - not a single star.

By 2,000 BC, the Egyptians and Mesopotamians marked the seasons by the constellations Taurus, Leo, Scorpio, and Aquarius. However, the marking of seasons by constellations may go back even further to 5,000 BC.

The precise origins of the twelve constellations of the zodiac are unknown. The original Babylonian zodiac consisted of eighteen signs; however the twelve sign zodiac developed later on � probably as twelve was the number of months in the Babylonian year. The present day names of the signs of the zodiac were first described by the astronomer and astrologer Ptolemy who lived in the Roman Province of Egypt between 120-180 AD.

Ptolemy�s Zodiac constellations


Zodiac in astronomy

In astronomy the zodiac constellations are a convenient way of marking the sun's path across the sky. The zodiac is also a way for astronomers to mark the path of the moon and planets. Apart from this role, the zodiac constellations have no extra significance to astronomers than any other constellation.

Unlike the zodiac signs in astrology, which are all the same length, the astronomical constellations vary widely in size. The boundaries of all the constellations in the sky were agreed upon in 1930. This was essentially a mapping exercise to make the work of astronomers more efficient.

Note: the boundaries of the astronomers� constellations are not the same as the astrologers� zodiac signs. Along with the twelve original constellations, a thirteenth constellation, Ophiuchus,was placed by astronomers within the zodiac. So, astrologers have 12 constellations of the same length but astronomers have 13 constellations of different lengths.

Table of constellations and zodiac signs

This table shows the dates the Sun enters and passes away from the zodiac signs and constellations as defined by astronomers and astrologers.

Note that there is no astrological sign corresponding to Ophiuchus - although the constellation was known by Ptolomy in about 150 AD. Ophiuchus occupies an honoured place along the zodiac: amidst the cluster of dust and clouds looking toward the centre of the Milky Way galaxy.

Ptolemy was a Greek or Egyptian mathematician, geographer, astronomer and astrologer

ConstellationSignAstrological zodiacAstronomical observations
AriesRamMar 21 � Apr 19Apr 19 � May 14
TaurusBullApr 20 � May 20May 14 � Jun 21
GeminiTwinsMay 21 � Jun 21Jun 21 � Jul 21
CancerCrabJun 22 � Jul 22Jul 21 � Aug 11
LeoLionJul 23 � Aug 22Aug 11 � Sep 17
VirgoVirginAug 23 � Sep 22Sep 17 � Oct 31
LibraScalesSep 23 � Oct 22Oct 31 � Nov 23
ScorpioScorpionOct 23 � Nov 21Nov 23 � Nov 30
OphiuchusSerpentHolder not used in astrologyNov 30 � Dec 18
SagittariusArcherNov 22 � Dec 21Dec 18 � Jan 19
CapricornSea GoatDec 22 � Jan 19Jan 19 � Feb 16
AquariusWater CarrierJan 20 � Feb 18Feb 16 � Mar 12
PiscesFishFeb 19 � Mar 20Mar 12 � Apr 19

Thanks to our resident astronomer JG

Halley's Comet

Named after Edmond Halley. It is a comet that can be seen every 75�76 years.

240 BC - First recorded sighting of Halley's comet

467 BC Chinese observe Halley's comet

The most recent appearances have been in 1835, 1910, and 1986.

Halley will next return in 2061 or 2062.

I went in to a pet shop and said, "Can I buy a goldfish?" The owner said, "Do you want an aquarium?" I answered, "I don't care what star sign it is."