The September night sky

By: CLIVE JACKSON

[email protected]

Clive Jackson is the Director of the Astronomical Observatory of Tavira (Sitio do Malhão, Tavira) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.

THIS IS the month of the Autumn Equinox, when on September 22, the Sun crosses the celestial equator on its journey south. This marks the end of summer and the beginning of autumn in the northern hemisphere.

Over in the southwest, just after sunset, the bright planet Venus will be seen very low on the horizon. The planet Mercury and Mars are close to Venus this month but much too faint to see without optical aid. As the month progresses, Venus climbs higher in the evening sky and by the month’s end sets more than an hour after the Sun.

Over in the south in the evening sky, Jupiter is unmistakably shining with a golden colour in the constellation of Sagittarius. The Moon will be below Jupiter on September 9. The constellation of Sagittarius contains the central area of our galaxy and if you follow the Milky Way straight up from Sagittarius on a clear dark night, you can see our Galaxy from the inside.

Signus-Rift

Practically overhead in the evening night sky, the Milky Way will be seen to split into two branches that run parallel to each other in the constellation of Cygnus. This is called the Cygnus-Rift and marks a lane of dark dust and gas that fills the spaces between the stars. This is the material that collapses to form new stars when stirred up by a shock wave from a supernova explosion. In fact the very atoms that make up our bodies were created when a giant star blew up in this area of the galaxy around five billion years ago.

The full Moon in September is called the ‘Harvest Moon’ and happens on September 15. This full Moon rises at sunset and for several nights before and after this date the bright Moon rises just as darkness falls. This was very helpful in allowing the gathering of crops to continue on into the night before the invention of electric lamps. Many societies based their social activities on the phases of the Moon, as it was important to be linked into the cycles of nature.

The Moon is at First Quarter on September 7, full on September 15 and Last Quarter on September 22 and New again of September 29.

For more information, please call Clive Jackson on 281 321 754, fax 281 324 688, email [email protected] or visit http://www.cdepa.pt