A constellation is simply a collection of stars, imaginatively linked together to represent a person, animal or object in the night sky. In this way astronomers are better able to organize the heavens into some recognizable form, and make locating stars and other astronomical objects easier. In 1922, the International Astronomical Union (IAU) recognized 88 modern constellations, 48 of which are based upon those recorded by the Greek astronomer Ptolemy around 150 AD in his treatise called ‘Almagest’.
Many of the constellations in use today have the names of characters from Greek and Roman mythology. These ancient civilizations believed their gods dwelled in the celestial heavens, and so naturally looked for and found those deities in the pattern of the stars. As well as gods, many mortals who had done something heroic got to live in the skies too, as well as the creatures and objects associated with their legends. Out of all the recognized constellations, 42 depict animals, 29 relate to objects, while 17 are either humans or mythological characters.
The location of many different constellations in the night sky is important, as together with some of their neighbors, they often recount stories from the world of legend. Likewise, constellation families refer to groupings of constellations within the same region of the night sky, some of which also share some kind of ancient mythological relationship. Of the eight constellation families, Hercules (19) contains the most constellations, followed by La Caille (13), Bayer (11), the Zodiac (12), Ursa Major (10), Perseus (9), Heavenly Waters (9), and Orion (5).
Zodiac is a Greek word meaning “pertaining to animals,” with the zodiac constellations included in the overall list of 88 constellations. The 12 traditional signs of the zodiac occupy an 18° wide band of sky centred on the ecliptic plane, which is the path the Sun, Moon, and planets seem to travel in the sky throughout the year. Naturally, this 360° ring marks the line along which any solar eclipse will also be seen to occur, and hence its name.
Throughout the year, the Sun appears in front of each zodiac constellations for a month or so, but as this takes place during our daytime, the view is obscured from view. If we could see the occurence, we would observe the Sun slowly drifting in an easterly direction onto a different zodiac constellation as it its continues its annual journey across the sky. The 12 zodiac signs are as follows: Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, and Sagittarius. In astronomy, there is also another constellation which intersects the ecliptic called Ophiuchus (serpent-bearer), which is sometimes referred to as the 13th zodiac sign.