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The start of Autumn

By: CLIVE JACKSON

Director of the Astronomical Observatory of Tavira and the Camera Obscura, specialising in education and public outreach.

[email protected]

WELCOME TO the September night sky. This is the month of the Autumn Equinox. This is the point in the Earth’s orbit around the Sun where the Equator is pointing toward the Sun and the axis of its rotation is in line with its orbit.

This signifies the start of autumn in the northern hemisphere and the end of summer. It means that on the actual date of the Equinox (September 23), everywhere on planet Earth will experience 12 hours of night and 12 hours of day.

If you look to the east after sunset, by the time it is fully dark, you should see the tiny cluster of stars rising called the Pleiades or the Seven Sisters. This pretty group of small bright stars is not a constellation but a galactic star cluster recently formed and is approximately 450 light years away. Most people can see six or seven stars in this cluster but through binoculars or a small telescope dozens of diamond-like stars can be seen sparkling away low in the east.

Harvest moon

As the Sun sinks lower in the daytime sky, the Full Moon rises higher in the nighttime sky. This is a special time of the year when a sequence of events happens naturally to the Full Moon. Normally, the Moon rises 30-60 minutes later each night, but around the Equinox time, the angle of the orbital motion of the Moon lies nearly parallel to the horizon so as the Moon moves eastwards in the sky, its time of rising changes very little for a few nights. This is called the Harvest Moon, as it was very helpful in the past in illuminating the fields to help bring in the crops quickly before autumn rains could spoil them.

At around midnight, in the east-northeast, the red planet Mars can be seen rising.

Mars is in the constellation of Taurus and, at the end of the year will come to opposition, that is when it is closer to the Earth. It will be on December 24.

Through a telescope, Mars will appear very small, but this winter, when it is at its highest in the night sky, any details on the surface will be a little easier to spot.

The Moon is at Last Quarter on September 4, New on September 11, First Quarter on September 19 and Full on September 26.