With the winter still grinding on in most parts of Canada, it is nice to be able to see in the sky that spring is on the way.
One of the obvious heralds of spring is the golden star Arcturus, which appears in the eastern sky in late winter. It’s easy to find, but to double-check, find the dipper, follow the curvature of the handle in the direction away from the bowl, and you will end up at Arcturus.
The other seasons have their herald stars too. In summer, red Antares will lie low in the southern sky. In the autumn, white Fomalhaut appears low in the Southeast. The star of winter must be Sirius, sparkling like a diamond in the dark winter sky.
Our ancestors imagined all the stars and other objects in the sky were fastened to a great crystal globe enclosing the Earth, which they called the “Celestial Sphere”. The Earth lay in the middle. They believed this sphere rotated once a day, turning in the westward direction, which would explain why we see stars rising in the east and setting in the west. In addition, they noticed that the planets, Moon and Sun move along a particular path around the sky, which they called the ecliptic. The Sun makes a complete cycle of the ecliptic each year. Its path around the ecliptic takes it through twelve constellations, which have become known as the “Signs of the Zodiac”.
Since the glare of the Sun makes it impossible to see whatever other stars are in the sky when it is above the horizon, we only get to see the stars during the night. As the Sun moves along the ecliptic, some constellations vanish into the glare and others are emerging, giving us different stars and constellations for each season. Of course today we know it is the Earth that goes round the Sun and not the reverse, but this explanation as to why we see different stars and constellations at different times of the year still applies.
The zodiacal constellation the Sun happened to be in when we were born is known as “our sign”. However, we cannot see that constellation on our birthdays because the Sun will be sitting there and the stars will be hidden in the glare. We have to wait until it has moved on, so we can see our sign and its neighbouring constellations in a night sky.
For example, the constellations we see high in the sky these spring evenings will be in the daylight sky in the late summer and autumn. These include the zodiacal signs for those with birthdays around that period. Find the Dipper and the two pointers opposite the handle, and instead of following them upwards to the Pole Star, go downwards instead, and you will find a constellation comprising a triangle and a reversed question mark that together look like a crouching lion. This is Leo, “The Lion”. Faint stars to the right of the question mark form Cancer, “The Crab”, and further west lies the Pleiades star cluster and Taurus, “The Bull”. That bluish-white star lower in the Southeast is Spica, the brightest star in Virgo, “The Virgin”. However, over the centuries, the wobbling of the Earth’s axis has made the zodiac slip forward one sign, so if you were born in spring, you are actually not an Arian; you are a Piscean.
Jupiter dominates the southwestern sky during the night. Saturn rises around 11p.m. The Moon will be full on the 27th.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory, Penticton.