Supermoon? What supermoon?

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[img_inline align=”right” src=”http://padnws01.mcmaster.ca/images/supermooncomparison.jpg” caption=”The ‘supermoon’ of March 19, 2011 (right), compared to a more average moon on December 20, 2010 (left). Photo by Marco Langbroek.”]Yes, it will be marginally brighter and larger, but Saturday's so-called “supermoon” is
not going to be noticeably different from the full moon of the month before or after.

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 “supermoon” 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, he says.

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 spoke-like patterns.

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