The supermoon: what is it and when is the next one?

A supermoon is the rare occasion when a full moon coincides with the moon being at its closest point to the Earth. When will the next supermoon be, and what does it involve?

The moon revolves around the Earth, each revolution taking 29.5 days. The moon’s orbit is elliptical, so the moon reaches its closest point to the Earth (perigee), and its furthest point (apogee), once each in every 29 days.

A supermoon occurs when the full moon coincides with the moon being at its closest point to the Earth – its perigee. In other words, we see the full moon when it is at its perigee, the closest it can come to the Earth. The same term is also used for the new moon. Thus, when there is a new moon (i.e. we cannot see the moon), and it is at its closest point to the Earth, this is also called a supermoon.

When is the next supermoon?

Because it requires several factors to coincide, a supermoon is a fairly rare event. The dates of next supermoons:

  • 2017 Sunday, 3 December
  • 2018 Tuesday, 2 January
  • 2019 Monday, 21 January
  • 2019 Tuesday, 19 February

What happens during a supermoon?

First of all, the moon will be at its biggest and brightest in the sky. The night of a supermoon is when you can observe the moon at its maximum size. Remember, though, that when the moon is rising above the horizon, there is an optical illusion that makes the moon seem very large. This is unrelated to the supermoon.

Secondly, the closeness of the moon to the Earth affects the tides, which are at their strongest during a supermoon.

Also, statistical studies suggest that the full moon influences people’s psychological and physical wellbeing, so this influence can be expected to be at its strongest during a supermoon. This is only a theory, though, requiring further evidence and studies.

What does a supermoon look like?

Bigger and brighter

During a supermoon, the moon looks approximately 7% bigger and 16% brighter than during an average full moon.

Biggest in winter

In winter, the Earth is closer to the sun, and during a supermoon the sun’s gravity pulls the moon more strongly towards the Earth. This makes winter supermoons look bigger than summer ones.

Biggest at moonrise

When the moon is rising, it appears just above the horizon and looks enormous and very beautiful. This is because it appears against the background of objects in the landscape, so we can compare its size with familiar things like trees, buildings, mountains etc. This effect is called the moon illusion.

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