On Sunday night, have a look at the moon — it will be bigger and brighter than at any other time this year.
The full moon on Sunday is a supermoon – one that is up to 14 per cent bigger and 30 per cent brighter than a regular full moon.
- Send photos of the supermoon to yournews@cbc.ca
It's also an extra-special supermoon – the biggest and brightest of three in a row – the previous one was on July 12, and the next one will be on Sept. 9.
That may make it a nuisance for anyone hoping to watch the Perseid meteor shower near its Aug. 12 peak, as the moon's glare will make it hard to spot many of the meteors.
But the supermoon is a special astronomical treat in itself, as it's literally the closest look you'll get at the moon all year.
In fact, that's what makes it appear bigger – during a supermoon, the moon is closer to the Earth than it is during a regular full moon. That's because the moon's orbit around the Earth is elliptical and lopsided, so that it's closer to the Earth on one side of the orbit than the other.
On average, the moon is 384,000 kilometres away, but it is about 363,000 kilometres away at the closest point, its perigee. And it is around 406,000 kilometres away at its furthest point, its apogee.
That means that a full moon that happens during the perigee is around 43,000 kilometres closer than a full moon during the apogee, making it appear bigger.
Supermoons are moons that take place on the same day as the perigee, and on average, they happen about once every 13½ months.
On Sunday, the moon will turn full during the same hour as the perigee – "arguably making it an extra-super Moon," according to NASA Science News. The astronomy news website EarthSky is calling it a "super" supermoon. Slooh, which streams astronomy events live online, is calling it a "mega-moon" and is hosting an observing event on the internet.
The Aug. 10 perigee, which takes place at 17:44 GMT (1:44 p.m. ET) will be the closest of the year – at that point, the moon will be just 356,896 kilometres away, according to the Lunar Perigee and Apogee Calculator hosted by Fourmilab.
According to NASA, the moon will become full less than half an hour later, at 18:09 GMT (2:09 p.m. ET)
In most populated areas of Canada, the moon will rise between 8 and 9 p.m. (although it will be a little later than that in the far north), and is best viewed shortly after moonrise for the most impressive effect – not only will it be closer and fuller at that point than later in the evening, but it tends to appear bigger when it's close to the horizon.