Why Saturday’s 'supermoon' will be beautiful, but not super

McMaster astronomer Robert Cockcroft, manager of the university's McCallion Planetarium, explains that a "supermoon" typically happens once a year, when the moon's elliptical orbit comes closest to Earth during a full moon. But the nickname makes it sound like a much bigger deal than it actually is.

"Will people know it's a supermoon on Saturday? Only if they've read about it," Cockcroft says.

The full moon at perigee, as astronomers call it, is 14 per cent larger than an average full moon, but barely larger than the full moons that come before and afterward, since the proximity of the full moon changes gradually over the course of the year.

The closeness of the "supermooon" does bring higher tides, but they rise only two or three centimetres beyond average, says Cockcroft, a PhD candidate in Astronomy and Physics.

While scientists don't consider the "supermoon" to be a big event, they do welcome the chance to talk about astronomy.

Cockcroft says myths about the full moon persist, despite scientific evidence that shows for example, that there is no link between lunar cycles and natural disasters, nor is there any relationship between madness -- or lunacy -- and a full moon.

One genuine mystery about a full moon is why it looks larger near the horizon than it does in the open sky.

"It's not fully understood exactly what happens," Cockcroft says. "It's definitely an illusion, and you can test this yourself."

The "moon illusion" makes the moon look like it's receding as it reaches the open sky, but if you hold up a dime against the moon in both places, the illusion is broken.

For those who will be looking at the full moon during Saturday's perigee, Cockcroft says its most fascinating features include the maria -- smooth fields of hardened lava once thought to be seas -- and the impact craters, particularly the rays that emanate from them where displaced matter has settled in spokelike patterns.

Those seas and craters lend themselves to imagination -- forming images of a man, a woman and even a rabbit.