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Supermoon will spring a total solar eclipse on Friday

03/19/2015 05:00 EDT | Updated 05/18/2015 05:59 EDT
Perfectly positioned celestial watchers are in for a triple threat this Friday as the skies have aligned for a rare flurry of activity. A total solar eclipse and a supermoon will usher in spring.

After a bitterly cold winter that set cold-weather records in some provinces, it seems fitting to celebrate spring's arrival with some cosmic pomp.

"It is unlikely ... for these things to line up," says Christine Wilson, president of the Canadian Astronomical Society.

Spring equinox marks 'the coming of spring'

March 20 is the first day of spring for those in the Northern Hemisphere. Southern Hemisphere residents will celebrate fall's arrival or perhaps mourn the end of summer.

At 6:45 p.m. ET, the sun will sit right above the equator — a moment known as the vernal equinox.

That moment hails "the coming of spring," says Paul Delaney, a professor at York University's department of physics and astronomy.

It's only twice a year that the sun's travels directly intersect with the celestial equator — the projected location of Earth's equator in space. About six months before the vernal equinox, the Northern Hemisphere welcomed fall and the Southern Hemisphere spring with the September equinox.

Canadians living where the sun hasn't yet set can look up to see it perfectly positioned above the equator. But "nothing unusual" happens in the sky, says Delaney, and only those aware of the equinox will know it's happening. He also doesn't recommend looking directly at the sun.

'Serendipitous' total solar eclipse

In a "purely serendipitous" coincidence, that same day, some earthlings can see a rare total solar eclipse, he says. It's an infrequent occurrence, that may only happen every 50, 100 or 1,000 years, depending on who you ask.

"Solar eclipses themselves are very rare."

A solar eclipse can only happen during one phase of the moon's roughly 29-day cycle. During its new moon phase, the moon slips between the Earth and the sun. The moon's shadow needs to hit Earth for humans to see a solar eclipse.

Since the moon travels on an elliptical orbit that is "tilted slightly" compared to Earth's orbit, says Wilson, that shadow doesn't land on Earth often. Most years, perfect conditions create two solar eclipses, according to NASA, though a few years have seen up to five.

Total solar eclipses — when the moon is so close to the Earth that it completely covers the sun — are even less likely.

Between 2000 BC and AD 3000, nearly 12,000 solar eclipses will happen, NASA estimates. Only 3,173 or about 27 per cent of those will be total solar eclipses, like Friday's.

Supermoon would be invisible without eclipse

That day's third celestial phenomenon, a supermoon, is likely helping fuel the full solar eclipse, Wilson says.

There's some debate in the astronomy world over what constitutes a supermoon. Most astronomers agree it's when the moon is closer to Earth than usual during its orbit. On average the moon is some 380,000 km away, but can be as far as 405,000 km. On Friday, the moon will be only about 360,000 km away, says Delaney, making it look much bigger than usual.

Some astronomers say the term supermoon only describes a moon during its full phase. However, Richard Nolle, who coined the term in the late 1970s, has written it can be a full or new moon. Friday's supermoon is a new moon.

When the moon is closer to Earth, it's more likely to create a total solar eclipse, says Wilson, because it's better able to cover the sun from our perspective.

Without the eclipse, humans wouldn't see Friday's supermoon. During the new moon phase, a moon is invisible to the human eye because its location makes it hard for people to see the sun illuminating it.

Right place, right time to see eclipse

The bad news is most Canadians won't get to see either the total solar eclipse or the supermoon. The best views will go to people in Europe and parts of Africa and Asia.

"You really have to be in the right place at the right time," says Delaney.

There's a small chance some St. John's residents could sneak a glimpse, but most Canadians will have to wait for two coming total lunar eclipses, says Gary Boyle, former president of the Royal Astronomical Society of Canada's Ottawa Centre.

Sept. 28, Ontarians and those living in the Maritimes can catch a lunar eclipse, while Ontarians and those living west of the province can see one on April 4.

The bright side is that total lunar eclipses are safe to view without eye protection, he says, while solar eclipses require special eyewear.

Without being able to see much of Friday's celestial flurry, Canadians can still take solace in one more thing, says Delaney.

"Enjoy the fact that at 6:45 [ET] that evening, spring has really arrived."

When phenomena will occur, by time zone

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