Missed the Harvest Moon? Here's Your Guide to Upcoming Supermoons

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On Tuesday evening, Australians gazing at the night sky might have spotted an exceptionally brilliant and noticeably large moon.

This marked the year’s first supermoon, also referred to as a ‘harvest moon’ — the bright full moon that appears closest to the beginning of autumn in the north and spring in the south.

The term comes from the era when farmers relied on the moonlight to gather crops late into the night in the northern hemisphere, particularly important during autumn’s abundant harvests.

If you missed the harvest moon, don’t worry; more supermoons are expected before the year concludes.

What is a supermoon?

The moon doesn’t quite orbit Earth in a perfect circle. Supermoons are full moons that coincide with the moon’s closest approach to Earth in its elliptical orbit, making it appear around 10 per cent larger because it’s closer to us.

The moon’s nearest point to Earth is known as perigee. During its 27-day orbit around Earth, the moon reaches both its perigee, approximately 363,000 km away, and its farthest point — or apogee — roughly 405,500 km from Earth.

Supermoons are rare and only a few occur each year, but another two can be expected in the coming months: on 5 November and 4 December.

Adam Batten, an astronomer from Swinburne University of Technology, said supermoons come in sets every year due to the position of the Earth around the sun and the position of the moon around Earth.

“Due to the Earth’s orbit not shifting much between months, supermoons can occur consecutively. If there’s a supermoon one month, it’s likely the adjacent months will also feature supermoons because their relative positioning doesn’t drastically change,” Batten remarked.

Beyond dominating the night sky, supermoons can also cause tangible changes on Earth in the oceans.

“Moons are obviously very linked to the ocean tides, so a moon that is closer to the Earth will have a bigger effect,” he said.

“Tides tend to be stronger during a full moon and even more so during a supermoon, leading to potentially larger king tides given the right conditions.”

Wait, what is a full moon again?

Batten said the different phases of the moon can be thought of as different positions around the Earth, and full moons happen when the moon is directly opposite the sun, with the Earth in between.

That’s because the sun’s light reflects off the moon back onto the Earth.

A bright, large moon behind clouds. A skyscraper can be seen next to it.

This week’s harvest moon, as seen from London. Source: Getty / Dan Kitwood

The opposite of a full moon in the lunar cycle is what’s known as a new moon.

“Aligning the moon on the same side of Earth as the sun results in a ‘new moon’, making it very dark as the sun, moon, and Earth line up,” Batten explained.

‘No-one talks about micromoons’

Conversely, a ‘micromoon’ occurs when the moon is at its greatest distance from Earth on its elliptical path, appearing much smaller.

This will occur in around March, Batten said, and while it may be less exciting to see, it provides better conditions for viewing the stars.

“No-one talks about a micromoon and it’s a real shame — it’s better for astronomy if the moon is smaller,” he said.

“The moon’s actually a little bit of a pain in the butt for a lot of astronomers; it ruins a lot of nights. A full moon blocks out so many stars, it makes it really hard to observe things from the ground. So, we actually like it when the moon is as dark as possible or as small as possible.”