While November 14 might just be another Monday for most of us, it’s a very special day for the Earth-Moon relationship. That’s because there’s going to be an extra special supermoon, one that hasn’t happened since January 26, 1948 – that’s sixty-eight years! If you miss this one, you will have to wait until November 25, 2034 to catch a sighting as close as this.
For the unaware, a supermoon happens because the Moon’s distance from Earth is constantly changing. You see, the Moon’s orbit is not a perfect circle but rather elliptical, which means it’s closer at some point, and then farther away a few weeks later. Plus, the Moon goes through phases – from new moon all the way to full moon – depending on the amount of light it receives from the Sun and its position.
When these two things – closest approach (the scientific term for it is perigee) and full moon – happen at the same time, we get a supermoon. If you’re interested, the technical term for a supermoon is “perigee-syzygy of the Earth-Moon-Sun system”, where syzygy means the straight-line configuration of the three celestial bodies.
The thing is, there is more than one prevalent definition for a supermoon. Some maintain that a supermoon occurs when the satellite’s centre is less than 360,000 kilometres (about 223,694 miles) from Earth’s centre. The average distance, by comparison, is 384,400 km (about 238,855 miles). By that logic, supermoons tend to happen every month or so.