Moon halo over Canberra
© Via Facebook
Moon halo seen in Canberra
Australians observed a mysterious halo around the moon on Wednesday night.

People living in New South Wales and the Australian Capital Territory observed differently sized rings around the moon, which appeared to change depending on where people viewing them lived.

Canberrans reported seeing a ring around the moon while others in the NSW towns of Moss Vale, Callala Bay, Woonona, Camberwarra and Culburra also saw it.

Many people posted pictures of the night sky phenomenon to social media, questioning what exactly had caused the ring to appear.

The Bureau of Meteorology's Helen Reid explained the moon ring was caused by cloud coverage over NSW and the ACT.

Moon halo Callala Beach, NSW
© Facebook
Moon halo seen from Callala Beach, NSW.
'It's just very fine cloud that would be scattering the light as it came through,' Ms Reid told Yahoo News Australia.

'With the moon light coming through quite well, there was probably an even covering for it to scatter the light, just like a rainbow sort of effect through the cloud droplet particles.'

More specifically, hexagonal ice crystals suspended in the clouds cause the moonlight to refract, creating a ring effect.

Moon rings are also known as winter halos as they mostly occur during colder months when there is more cloud coverage.

They are also known as 22 degree halos as light is required to deviate by a minimum of 22 degrees to create the halo effect.
Moon halo Woonona
© Facebookj
Moon halo seen from Woonona, NSW.
The optical phenomenon can also be caused by sunlight, which is responsible for the rings often seen around the sun.

Twenty-two degree halos are often confused with coronas, which also have a ring-like effect.

But the key difference between 22 degree halos and coronas is the the former is caused by ice crystals while the latter is caused by water droplets.