What’s up? The night sky August – September 2023

Small white dots on a black sky

Night sky highlight for July to September

Image shows the western sky around 6.30pm on 18 August with Mercury, Mars, a thin crescent Moon and the star Denebola to the right.

Made using the free software Stellarium: http://stellarium.org/

After the excitement of the solar eclipse in April we’re back to concentrating on the night sky for July through to September.

The evening sky in July sees three planets visible in the west: Venus, Mars with the elusive Mercury from mid-month. In August Venus is replaced by Saturn in the evening sky, with both Saturn and Mars still visible in September. Mercury is generally a difficult planet to view as it is always close to the Sun so only ever visible around sunset or sunrise.

There are two full Moons in August, the first on 2 August and the second on 31 August. The Moon is at perigee for each of these, meaning it is slightly closer to us than normal due to its elliptical orbit. Sometimes termed Supermoons, these will appear slightly larger than usual though in practice most people would not be able to tell the difference. Regardless, it is always stunning to watch a full Moon rise in the east.

Winter months as always provide the best views of our galaxy, the Milky Way. Around a New Moon, when night skies are darkest, the dust lanes and bands of stars are clearly visible. The centre of our galaxy is found in the constellation of Sagittarius which is high overhead in the evening sky in September. Whilst not visible to our eyes or optical telescopes, the centre of the galaxy contains a supermassive black hole, Sagittarius A* (or Sgr A*). It has a mass of about 4.154 million times that of our Sun. Using radio telescopes, astronomers can image the disc of material accreting around the black hole.

A glowing red dough nut on a black background

This is the first image of Sgr A*, the supermassive black hole at the centre of our galaxy. The new view captures light bent by the powerful gravity of the black hole. Credit: Event Horizon Telescope (EHT) Collaboration

Rob Hollow, Education Manager, CSIRO