As the cool winter temperatures start to settle in around us here in Sydney, the southern night sky gears up for a dazzling show that is the envy of all northern hemisphere skywatchers and observers. We get the special treat to enjoy the wonders of our home galaxy, the Milky Way.
That’s because during the southern hemisphere winter months, the centre of our galaxy is high in the sky, with the extended arms and disc of the magnificent structure stretching from horizon to horizon. This gives us a beautiful view of many star clusters, nebulae, bright stars of many different colours, and the marvellous dust lanes that remind us that we are looking inwards towards the centre of our home galaxy, from the outer suburbs.
July also features a chance to catch the gas giant planets (Jupiter and Saturn) in our solar system as well as some of the inner planets – like Mercury high in the sky early in the month, or Venus catching up to Mars around July 15.
When we look at the night sky with our eyes, we are catching waves of light (or electromagnetic radiation) in what is known as the ‘optical bands’. Simply put, these are the visible colours of the rainbow that your eyes have evolved to tune into.
But the electromagnetic spectrum stretches well beyond the optical bands and into other frequencies. When we go higher than optical, we reach the ultraviolet bands – the same ones that cause many of our skins to tan – then x-rays and gamma-rays. Thankfully for us – and all life on Earth – our precious atmosphere does a pretty good job at blocking out most of these forms of light, as they can be harmful to living things.
Then, if we go lower than optical, we first reach the infrared bands. These are the heat that your skin is sensitive to – like feeling which direction the warmth of the Sun is coming from, even when you close your eyes. Going a little lower, we get to the microwave bands – the same stuff that reheats your cup of coffee at home – then finally we get to the radio bands, which is what we hear in our cars and at home.
The thing is, different objects and different processes in space send out all of these different frequencies – our Sun, for example, sends out radio waves, heat, visible light, UV light and x-rays. Many objects in space do this. And by studying these different bands, we can learn about different occurrences about each object. It’s like having x-ray glasses or radio ears!
In my upcoming livestream with Sydney Observatory, we will check out some of these objects – like the supermassive black hole in our galactic centre, or a few galaxies – even the Moon – in different wavelengths as well as optical, learning about each feature. I hope you can join me on our multiwavelength adventure around the galaxy, and beyond!
Rami Mandow is an astrophysicist and the founding director and editor of Space Australia. He is hosting Sydney Observatory’s next Southern Sky Livestream on Friday, July 16 at 7.30pm. You can register on the Facebook event and watch along from home.
Want to see more? Broadcasting from the Sydney Observatory, and starring a new guest astrophysicist each month, see deep-sky objects and other highlights of the Southern sky live through Sydney Observatory’s telescopes. See the line-up and register to watch here.