The term blue moon has two definitions, depending on who you ask. In the 1930s, the Maine Farmers’ Almanac invented the name blue moon when it divided the year into four seasons, separating them with the equinoxes and solstices, giving a name to the three full moons in each season. Very occasionally, a season had four full moons instead of the usual three, and the blue moon was given to the third of the full moons.

Some time later, blue moon became the term to describe the second full moon in a single calendar month. Despite it not being the original definition, this is the one that seems to have become most popular. Whichever way you describe it, the Moon doesn’t appear blue, but despite that it’s still worth going out and watching the Moon, as blue moons only occur once every 2 or 3 years (depending on your definition). The next blue moon after this will be either 31 May 2026 or May 2027.

Pack an evening picnic. Find a location where you have a clear view to the eastern horizon. Rally family and friends and enjoy a lovely evening watching as our nearest celestial neighbour rises.

When to look:

20th August, from 5.15pm. The Sun won’t have set at this time, so it will be harder to see the Moon rise. However, as it gets a bit darker, you’ll have no trouble!

21st August from 6:28pm. The Sun will have just set, making it easier to see the Moon as soon as it starts to rise.

Which direction to look: The Moon rises in the east.

Something interesting

Because the Moon’s phases cycle, on average, 12.37 times yearly, once every 2.8 years, a year contains 13 full moons rather than the usual 12. This awkward ratio of 12.37 is because the Earth’s seasons are determined by the period of the Earth’s orbit around the Sun, while the Moon’s phases are determined by the period of the Moon’s orbit around the Earth. 

What craters can you see on the Moon?

When you observe the Moon, take it one step further and identify a crater or two. Some great tools help you out with maps of all the features on the surface of the Moon. Before you know it, you’ll point out the Tycho Crater or the Sea of Tranquillity to friends and family. Try some of these free apps and software:

Moon Phase and Libration Visualizations

Moon Globe (for iOS)

Moon Atlas 3D (for Android)

LunarMap Lite (for Android)

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There’s always something interesting happening in the night sky and country WA is the best place to catch all the action.