Australasian Science: Australia's authority on science since 1938

September 2012 guide and star chart

By David Reneke

Your guide to the night skies this month.

Someone who once tried to count them said there were more stars in the Universe than heartbeats for every human who ever lived! Now that’s a big number. Have you ever wondered where the names of some of the stars come from?

There are billions and billions of stars but only some 6,000 or so are visible to the naked eye. Of those only a handful of the brightest have proper names like Sirius or Betelgeuse, the rest are simply given letters of the Greek alphabet.

Sirius is well known because it is the brightest star in the night sky. It was equally important to the ancient Egyptians who associated it with their goddess Isis. And you’ve probably heard of Betelgeuse because of that movie even if it’s often mispronounced as ‘Beetle-juice’ right? Even our Australian aborigines have legends about the stars and constellations in their Dreamtime.

Heading towards Christmas we’re also heading into the best sky watching period, and things are going to get interesting. So, grab your telescope, I’ll grab mine, and I’ll meet you on the lawn.

Saturn makes its way towards the western horizon this month with Mars below. The bright star Spica (Virgo) can be found sitting to the left of Saturn. On the 18th the crescent Moon joins the pair. Then on the 30th, Mercury can be seen below Spica, with Saturn above and to the right.

Rising around midnight in the east Jupiter still shines as the king of the planets. Although it’s late, this is a good time to view and photograph Jupiter and its moons, and its visible right up until sunrise!

Venus remains in the eastern sky this month to continue its stint as the ‘Morning Star.’ Catch it below Jupiter blazing away in brilliant white light. During the early part of the month, the twin stars of Gemini, Castor and Pollux, can be found to the left of Venus. The Moon sits alongside Venus on the morning of the 13th.

The Spring Equinox occurs on September 22 at 2.49pm. The Sun shines directly on the equator and this is the time when many people believe that we experience 12 hours of equal day and night throughout the world. This is also one of only two days in the year when the Sun rises due east and sets due west.

Remember, our Solar System is basically divided into two halves. The inner half includes Earth and Mars, which are known as the rocky planets, and are quite small, made of rock and have thin atmospheres or none to speak of, in the case of Mercury.

The outer planets, Jupiter, Saturn, Uranus and Neptune are known as the Gas Giants, and are all huge and made mainly of gas. Pluto, on the outer extremity of the Solar System, is small and made of rock and ice and, as we all now know, is no longer classed as a true planet.

Haven’t got a telescope yet? Probably the most important piece of advice I have is the best telescope for you is the one you will use most often. There’s no point in buying a big complicated piece of equipment when a smaller more modest setup will mean you can be up and running in minutes.

Back outside, gaze directly overhead at sunset. The curl of the Scorpion’s tail can be seen near the teapot shape of Sagittarius. The Milky Way spans the sky overhead, looking splendid as it stretches almost north -south

Now turn eastwards and you should notice an orange star looking a little lonely with not many other stars nearby. This is called Fomalhaut, the mouth of the Southern Fish. Lower down, rising out of the south east is the brilliant star Achernar.

Wow, just seeing that star in the evening again reminds me that summer is not too far away!

David Reneke is a feature writer for major Australian publications including Australasian Science magazine and a science correspondent for ABC and commercial radio. Get David’s free astronomy newsletter at www.davidreneke.com