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What is a Blue Moon? | August's Sturgeon and Blue Supermoons 2023

2023 is flying by and it's now almost August, a month which will bring us two full moons — and two supermoons, at that! The Sturgeon Moon will come at the start of the month, on the 1st, and the Blue Moon will arrive at the end, on the 31st.

The last Blue Moon was in 2020, and the last 'blue supermoon' was in 2018, so August's Blue Moon is certainly one to look out for. In this article, we'll explore supermoons, what a Blue Moon actually is, and where August's full moon gets its name from. At Sent Into Space, we're certainly excited to see two full moons inside of one month!

What is a supermoon?

The Moon orbits the Earth once every 28 days (approximately). The Moon's furthest point from the Earth is called its apogee, and its closest its perigee. A supermoon is a full moon which occurs when the moon is at or near its perigee, and as such, supermoons were historically known as perigean full moons. The term 'supermoon', however, was coined in 1979 and has quickly become the more popular term, perhaps owing to its accessibility.

Full moon, blue supermoon

Supermoons are closer to the Earth than other full moons, and so to anyone observing one from the Earth's surface, they are brighter and larger than any other full moon. In fact, a supermoon is approximately 27,000 miles closer to Earth than a micromoon, the full moon which occurs when the Moon is at its apogee.

Where does the Sturgeon Moon get its name from?

August's full moon is called the Sturgeon Moon. Sturgeons are a prehistoric fish, having been around for 200 million years, since the Mesozoic Era. The August Moon was named the 'Sturgeon Moon' by North American fishing tribes who noticed that the fish appeared in greater numbers during this month than any other.

Sturgeon fish swimming in a dark river illuminated by a light

The name 'Sturgeon Moon' may be the one that we use most, but it isn't its only name — August's moon has also been called the Ricing Moon by some indigenous American tribes such as the Ojibwe people, and the Grain Moon by the Anishinaabe people.

What is a Blue Moon?

You have probably heard some variation of the phrase 'once in a blue moon' to explain the occurrence of something rare. But what actually is a Blue Moon?

The first thing to establish is that it's not actually blue in appearance — a Blue Moon looks the same as any other full moon. We actually don't know where the Blue Moon gets its name from. It's thought it could have originated from a mispronunciation which caught on, or a 17th century idiom, but we don't know for sure.

Clouds illuminated by a full moon

When it comes to defining a Blue Moon, there are two different definitions. The most popular definition — the idea that a Blue Moon is the second of two full moons in a month — is actually not correct. A Blue Moon is the third of four full moons in an astronomical season – which can sometimes be the second in a month, but this is not what makes it blue.

'Astronomical seasons' may sound complicated, but they are actually fairly simple. An astronomical season is demarcated by a solstice and equinox, i.e. spring begins at the spring equinox, summer at the summer solstice, autumn at the autumn equinox, and winter at the winter solstice.

A solstice occurs when the Earth is at its closest (summer) or furthest (winter) axial tilt from the Sun, and an equinox is when the Earth's axis is tilted almost equally towards and away from the Sun. The equinoxes happen in March and September and the solstices in June and December — but which one is spring, summer, autumn, or winter depends on where on the planet you are, e.g. the Northern or Southern Hemisphere.

There are usually three full moons in an astronomical season, and so when there are four, the third of these is a Blue Moon. Blue Moons happen generally once every two years, hence the phrase 'once in a blue moon'.

Seeing the full moons this August

The Sturgeon Moon is the first of August's full moons, and will be visible in the sky on Tuesday the 1st of August. According to the Greenwich Royal Observatory, it'll be at its fullest at 7.31 pm — so if you want to see it, it seems that you won't have to stay up too late!

The Blue Moon comes at the other end of the month, gracing the sky on Thursday the 31st of August. This one will be at its fullest at 2.35 am, but will appear full all night. As both of these moons are supermoons, they will look larger and brighter than a full moon usually does from Earth — and they're the only supermoons we'll see in the sky this year, so make sure to take a look!


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