A guide to what's up in the sky for Southern Australia
Starwatch May 2024 - Thu 2nd May 2024
Published 2nd May 2024
A myriad of bright stars adorn the late autumn evening sky.
Galaxy NGC 5128 - Wed 1st May 2024
Published 1st May 2024
Galaxy NGC 5128—Centaurus A
Comet Pons-Brooks - Wed 10th Apr 2024
Published 10th Apr 2024
Looking west on the evening of April 27., 30 minutes after sunset. Locate the orange star Aldebaran, then scan to the left until you come to a fuzzy spot in the sky. Train your binoculars on it, the comet will be 239 million kilometres away. Graphic generated with Stellarium planetarium software.
M104 - The Sombrero Galaxy - Tue 9th Apr 2024
Published 9th Apr 2024
M104 - The Sombrero Galaxy. Distance: 31 Million Light Years
Starwatch - April 2024 - Mon 8th Apr 2024
Published 9th Apr 2024
Some of the brightest stars in the whole sky can be seen during these crisp autumn evenings.
Starwatch - March 2024 - Wed 6th Mar 2024
Published 6th Mar 2024
What a wonderful time of the year this is to be observing the night sky. The weather is warm, the nights clear, and the Milky Way shines directly overhead!
Object of the Month - Mon 4th Mar 2024
Published 4th Mar 2024
Eta Carinae Nebula (NGC 3372)
Distance: 7500 Light Years
Right Ascension: 10 : 43.8 | Declination: -59 : 52
What a wonderful time of the year this is to be observing the night sky. The weather is warm, the nights clear, and the Milky Way shines directly overhead!
Also overhead, are the two brightest stars in the whole sky. A little over to the north is Sirius, and a little to the south is Canopus.
It’s not just these two stars that make the summer night sky so glorious. Let's begin low in the north. Using this month's star chart, find Capella. Note that the star is a golden yellow in colour. It's the same type of star as our Sun, albeit a trifle larger. Unseen, except in the largest telescopes, Capella has 3 other stars that revolve with it around a common centre of gravity. At approximately 50 light years distant, the light from Capella now reaching us left at the time when palaeontologist, Donald Johanson, discovered a 3.2-million-year-old hominid skeleton in Ethiopia on November 24, 1974. The skeleton, later called Lucy, was the oldest known example of a human ancestor to have been found.
Higher and to the north-east, we find Castor and Pollux. They form the heads of the twins of Gemini. Pollux is about 11 times the diameter of our Sun, 35 times as bright, and almost twice as massive. And it’s that mass that determines the future of Pollux.
Whilst there’s no formula for predicting how long a person will live; a single number determines how long a star will live: its mass. Genetics, nutrition, exercise, and other factors all play a role in our longevity. But that’s not the case with the stars.
Mass is what makes all the difference in a star’s lifespan. At 2 billion years of age, Pollux is roughly half as old as the Sun. But it’s already finished its “normal” lifetime; the phase the Sun is in right now.
During that normal lifetime, a star “burns” the hydrogen in its core to make helium. When the hydrogen is gone, the core gets smaller and hotter, so it begins to burn the helium to make carbon and oxygen. At the same time, its outer layers puff up like a balloon, making the star much brighter. That also makes the star’s surface much cooler, so it glows reddish-orange, as Pollux does now. Because of its larger mass, it burns everything faster!
Over time, Pollux will get even bigger and brighter. Then it will expel its outer layers, briefly surrounding itself with a colourful bubble of gas. That bubble will quickly fade, though, leaving only the star’s small dead core; a hot ember known as a white dwarf. The same fate awaits the Sun, perhaps 4-5 billion years in the future.
You can see the 9-day old gibbous Moon just above Pollux on the evening of March 19.
You will notice that the bright moonlight has a significant impact on stargazing. Many of the fainter stars become invisible to the naked eye reducing the splendour of a dark sky. However, it can also be a beautiful addition to a night-time scene. Like the Full Moon rising over a body of water, or illuminating a rustic rural scene.
A couple of examples for you to look at are shown below.