A common saying about something very rare is that it only happens “once in a Blue Moon”. This year we will have two chances for that, and the first will be worth watching.
A “Blue Moon” is the name given to the second full moon in one calendar month. In most years, there is only one full moon each month.
The full moon on Wednesday January 31will be just such a moon. It is also a “supermoon”, meaning the moon is closer than normal to the Earth.
However, the January Blue Moon has another interesting feature. Because it will be directly opposite the Sun, the Earth will cast a shadow over it, causing a lunar eclipse. For a period of time, the moon will be blotted out from the sky, then return.
The time of the eclipse, and how long it lasts, depends where you are in the world. For Australians, the eclipse begins son after sunset, at 9:51pm (AEST), and lasts for just over five hours.
Some social media posts claim that this is the first Blue Moon total eclipse in 150 years, but in fact that is only true for the American continents.
There will be a second Blue Moon this year, on 2 March. Blue Moons usually occur once every few years, but two Blue Moons in one year is much rarer, occurring only every 19 years. So the next time there is a Blue moon in both January and March will be 2037.