The behind the stars star signs

An astronomer's journey through the real zodiac

- Mary McIntyre

Mary McIntyre takes us on a guided tour of the 13 zodiacal constellations and their most beautiful night-sky jewels

We've all heard of the zodiac and 'star signs', whether we believe in the latter or not. But you may be unaware that the signs of the zodiac are real constellations in the night sky, just waiting to be observed and explored.

The origins of the zodiac lie in early civilisations that relied on the movement of the Sun, Moon, planets and stars to mark the passage of time. Our ancestors realised the Sun and planets passed through a small group of constellations along an imaginary line known as the 'ecliptic', which is the plane of the planets' orbit around the Sun, as seen from Earth. The ancient Greeks called this the zodiac, meaning 'circle of little animals' because most of these constellations were named after animals. In astrology, the zodiac is divided into 12 'signs', but in astronomy we know the Sun actually moves through 13 constellations over the year (the 'extra' one being Ophiuchus) and most are visible for several months. They climb the dawn twilight in the east and are visible earlier each night as they move westwards until, months later, they sink into evening twilight in the west. As a result, the path the Sun takes during a year appears to be moving backwards against the zodiac (see chart overleaf). Due to precession - the slow change in the direction of Earth's rotational axis - the Sun no longer travels through them on the same dates as it did when the signs were first assigned.

Let's take an astronomer's tour of the real zodiac - the 13 constellations and the best night-sky targets to see in them.

Aries
Best time to see: September to February
Sun transits this sign: 19 April-14 May