It’s what people have been calling the supermoon, but it may not look as super sized as you may expect.
Professor of Physics and Astronomy at Western, Robert Cockcroft, says the term has been made up by the media. Astronomers actually prefer to call it a full moon at perigee.
“Perigee basically means that the moon is closest to the Earth. The moon in it’s orbit isn’t always at the same distance from us. The reason why everyone is getting excited at the moment about this particular supermoon is because the moon is as close as it has been for decades and it won’t be this close again for another couple of decades.”
The moon will be 14% larger and 30% brighter, but when observing it, it may not be noticeably larger. Professor Cockcroft uses an analogy with pizza.
“If I showed you say a 14 inch pizza versus a 15 inch pizza than I put them both behind my back and brought one of the pizzas out and showed you, could you guess whether it’s the 14 or 15 inch pizza? Probably not. Same with the moon. So it might not look that spectacularly big.”
This is part of the reason astronomers don’t use the term supermoon because the size is not as dramatic as the name makes it out to be, and many people compare it to the size of the moon they see on the horizon.
“This is a real effect, the moon is getting closer to us. It is not a moon illusion which people sometimes see when the moon is on the horizon versus when it’s high up in the sky. That’s just your brain playing tricks on you.”
Cockcroft says you can use a dime to test a moon illusion. If you hold one out straight in front of you and align it with the moon, and then again over head when the moon is higher up in the sky you will see that it fills the same space and is in fact a moon illusion.
There are still practical implications to learning about the supermoon.
“The moon effects the tides on the Earth. If you are close to tidal regions, during the period of the supermoon you will have larger than normal tides and lower than normal tides as well.”
The Cronyn Observatory at Western will be open to the public from 7:00 to 9:00pm with multiple telescopes available to observe the moon and other sights of interest.