Count the stars in the Southern Cross during winter solstice and map light pollution in your suburb

Winter is the best time to see the rich beauty of the sky when we look straight into the centre of the Milky Way. And Sunday night is the longest night of the year in the Southern Hemisphere, which makes it perfect for counting the stars in the Southern Cross. If you do, you’ll contribute to a world record attempt to map light pollution across Australia.

Whether or not you get to see full beauty of the Milky Way — or even the Southern Cross — depends upon where you live, says astronomer Fred Watson. If you’ve struggled to find the Southern Cross from your backyard during COVID you’re not alone. In areas that have high levels of light pollution you can see only four — or even three — of the constellation’s main stars. While satellites can detect raw points of light across the globe, there is very little data about how Australians are affected by light at ground level.

But if you count how many stars you can see in the Southern Cross this Sunday night, during the winter solstice you could help fill in some of the gaps. The information collected contributes to the Globe At Night international citizen science program, which measures light pollution around the globe. There were only six readings from Australia until April, when the Australasian Dark Sky Alliance, ran its first star count during lockdown. Now there are 770. The idea is to do the star count again on a much larger scale to get a baseline across Australia and New Zealand, says Marnie Ogg, who heads the Alliance.

Counting stars in the Southern Cross for this weekend’s world record attempt is easy and no special equipment is needed. All you need to do is count how many stars you can see using just your eyes (not binoculars or a telescope) and match it to the maps on the website that best represents what you can see. These maps provide an approximation for the star’s magnitude, and the Bortle Scale. You can also note cloud conditions and nearby light sources. And don’t let any cloud cover — even rain — put you off. “Even if your sky is cloudy … it doesn’t negate the entry,” Professor Watson says.