WELCOME TO the September night sky. This is the month of the autumnal equinox, when the Sun crosses the celestial equator or, in other words, takes its journey southwards. It will be on September 23 this year and it means that, at this time, the whole world will have equal length of day and night. It also marks the end of summer and the start of autumn in the Northern Hemisphere.
Just after sunset on September 7, the Full Moon will rise in the east, but it will have a slightly strange appearance. The upper part of the disc of the Moon will be dark in colour, as the shadow of the Earth will be seen to fall on this part. This is a partial lunar eclipse. Although not particularly rare, it is worth seeing.
Another sight worth looking at will be in the early evening of September 12, when the Waning Moon will pass in front of the Seven Sisters star group. The Moon will take several hours to pass the cluster completely, because this tiny cluster is actually six times bigger than the Moon. Although it might seem that the Moon is quite large in the sky, it is only one-half of a degree across, and it would take 720 Full Moons to go completely around the horizon!
After midnight, in September, the grand constellation of Orion will be rising in the east. This is a sure sign that summer is over and it is now down hill all the way to winter.
Low in the west now, just after sunset, the planet Jupiter is rapidly disappearing in the evening twilight.
The Moon is Full on September 7, Last Quarter on September 14, New on September 22 and First Quarter on September 30.
• Clive Jackson is the director of the Astronomical Observatory of Tavira (Sítio do Malhão) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach. Tel 281 321 754, Fax 281 324 688, e-mail [email protected] – visit www.cdepa.pt