That moon is Super!

Anyone who is into Omens is probably having a field day right about now, especially if they work for CNN.  It's an unquiet Earth, this blue orb where we live. 

Tonight is going to bring along yet another omen -- a full moon which appears to be much larger than normal.  Much larger.  What can this mean!?? Run!!! Toss some virgins into the nearest volcano...  Gather together in loud lamentation! Repent! (well, the repent bit is usually always a good bet, but still...)

Settle down. Enjoy.  It's the March full moon.  And yes, it's HUGE.  That's because the Moon, our planet's faithful companion, is at its closest approach to the Earth in two decades.  It's what Science calls Perigee -- as opposed to Apogee when it's at its furthest reach.  Yes, this may well bring with it stronger tides, as it has every time it has come that close, but that is a normal part of the Moon's orbiting pattern. Been there, done that. The Moon swings around Earth in an elliptical orbit, meaning that it is not always the same distance from the Earth. The closest the Moon ever gets to Earth is 364,000km, and the furthest is ever gets is around 406,000km. This Full Moon on March 19, 2011 will see a slightly closer approach of 357,000km).

 
Twenty years is a good long time, though, and there will be plenty of people who have never had the chance to witness this.  Particularly if the last one happened on a cloudy night... which would push back the timeline considerably.

And yes, it looks bigger -- a full moon at perigee will appear 10% larger than a full moon at apogee...

Here's the fun bit -- while it will indeed appear much bigger than normal, it really isn't. It's all an illusion, a trick of the eye.   Nobody changed the actual size of the Moon!

Ebbinghaus Illusion: both orange dots are the same size!

The full moon always looks larger on the horizon than it does in the sky. It's called the Moon Illusion. When the Moon is low on the horizon there are lots of objects (hills, houses, trees etc) against which you can compare its size. When it’s high in the sky it’s there in isolation. This createssomething akin to the Ebbinghaus Illusion, where identically sized objects appear to be different sizes when placed in different surroundings.

This is a welcome Full Moon -- in older times, people gave names to all the full moons. In March, as temperatures began to warm and the earth to thaw, earthworm casts appeared. This heralded spring, the return of robins, the approach of the planting season and the end of winter's lean menu.  It was dubbed The Worm Moon.

Here in the northern regions, tribes knew this as the  Crow Moon -- because the cawing of the crows signalled winter's end. If you've been outside lately, you've probably heard them!  Some tribes called it   Crust Moon, because the snow cover becomes crusted from thawing by day and freezing at night.

The Sap Moon, marking the time of tapping maple trees, is another variation. To the settlers, it was also known as the Lenten Moon, and was considered to be the last full Moon of winter.

But tonight, March 19, it's simply the Super Moon -- a marvellous little chance to interact with science, learn cool new phrases like the Ebbinghaus Illusion, and say a little "Welcome Back" to spring.