Every Monday really is longer than the last, says astrophysicist Dr Brad Tucker from his post at the Mount Stromlo Observatory.

That's because each year the moon inches away from the Earth by about 4 centimetres, lengthening our days as it slowly pulls free of the planet's orbit.

But, this Monday at least, the moon will be closer than usual as the first and last supermoon of 2017 rises.

A "supermoon" is a rare lunar event in which the moon appears up to 14 per cent bigger and 30 per cent brighter than normal. 

Known as the "cold moon" in the northern hemisphere, it happens when the moon is not only full but orbiting close to Earth.

On average, the moon is shining 382,900 kilometres away in space, but its orbit isn't perfectly circular. According to Dr Tucker, it can vary by 50,000 kilometres.

"That's quite a lot when you think about it," he said.

On Monday, less than a day after the official December full moon, the moon will make its closest approach to Earth for the month, coming within 357,492 kilometres of our planet at about 3.45am. 

But Dr Tucker said the best time to see the main event will be at moonrise a little after 8pm on Sunday, as the moon lifts clear of the horizon.

And there's no fancy gear required. 

"Looking through a telescope, you almost don't want to do that because it's so bright it's almost blinding," Dr Tucker said.

"This is a good phenomenon to see with the naked eye."

As to the best vantage point in Canberra, Dr Tucker suggests making the climb up Mount Ainslie or Black Mountain tower where the city will be spread out below.

"You'll see all the houses and it will look bigger on the horizon against faraway objects."

Of course, with the skies darkening for what is promising to be an almost biblical downpour this weekend, conditions to view the supermoon will be less than ideal.

But, while the weather might be wild, Dr Tucker said the full moon will have no effect on our moods.

"Waking up at 4am on a Monday to see the moon will have a worse effect on your mood than the actual supermoon!"

Fun supermoon facts:

• While we had no less than three supermoon events last year, this is the only observable supermoon of the year.
• The supermoon on November 14, 2016, was the closest since January 26, 1948.
• The point on the Moon's orbit closest to Earth is called the perigee and the point farthest away is the apogee.
• A micromoon is a full moon or new moon that takes place when the centre of the Moon is further than 405,000 kms from the centre of Earth.
• Although the Sun and the Moon's alignment cause a small increase in tectonic activity, the effects of the supermoon on Earth are minor and they definitely aren't linked with mood changes in people.

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