The September night sky – 9pm

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.

Welcome to the September night sky. This is the month of the Autumn Equinox that marks the official end of summer in the northern hemisphere.

The sun is moving southwards in the sky and this causes the days to get shorter and the nights longer.

Normally we do not notice this change much, but at the Equinox the rate of change is at its greatest and this is when we first become aware of the nights “drawing in” due to the sun setting several minutes earlier each day.

The bright planet Venus is still visible over in the west at sunset but it is getting lower each day. On September 11 the thin Moon will be close to this planet.

September is the month of the opposition of the giant planet Jupiter and on the 21st it is at its closest to Earth in the constellation of Pisces.

This planet is 12 times the diameter of Earth and 1,300 times the volume, and on the night of 23rd the full Moon will be close to Jupiter.

This year Jupiter is lined up with distant gas giant planet Uranus, although the pair will appear quite close to each other they are in reality very far apart, they appear close due to the fact of them being on the same line of sight, and this gives you your best chance of finding this distant planet if you have never seen it before.

A small telescope or a pair of binoculars would have to be used as Uranus is just slightly too faint to see with just your eyes alone.

Uranus is exactly one degree to the north of Jupiter and will appear as a pale greenish star like object about the same brightness as the Moons of Jupiter.

This distant planet is actually four times the diameter of Earth but it is more than two billion kilometres further away than Jupiter and that is why is appears to be so small.

On the southern horizon the summer constellations of Scorpios and Sagittarius are now fading in the southwest after dark to be replaced with the autumn stars of Capricorn and Aquarius. While over in the north we can just see the constellation of the Great Bear or Ursa Major. It is right on the horizon and therefore not well visible this month.

High overhead during late September nights we can view the constellations of Pegasus and Andromeda. Just visible on a clear dark night is a galaxy in the upper part of Andromeda. This galaxy is more than two million light years away and is generally regarded as the most distant object visible with the unaided eye.

The Moon is at last quarter on the 1st, new on the 8th, first quarter on the 15th and full on the 23rd.

Clive Jackson is the director of the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.

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