Mercury makes rare transit of the sun today

Canadians got a rare view of Mercury as it crossedin front of the sun today.

Mercury beganmaking its way across the face of the sun at 7:12 a.m. ET andcompleted its crossing at 2:42 p.m. ET, moving from east to west.

It's not safe toview such an event without proper solar filters, but solar-filter telescopes wereavailable at public observation events held across the country by astronomy clubs, observatories and universities. Mercury is so small that astronomerssaid it wasunlikely to be visible without binoculars or a telescope (equipped with solar filters, of course).

• Mercury transit: How to watch the rare event
• Local publicviewingsof the May 9 Mercury transit across Canada

For those who couldn'tmake it to one of those events, NASA wasstreaming a variety of coverage that includeda panel discussion with NASA experts about the event, along with live images from the Solar Dyanmics Observatory satellite.

The event was also beingstreamed online starting 7 a.m. ET by Slooh, an organization that broadcasts celestial events online from telescopes around the world.

Transits of Mercury happen only about 13 times a century the last was in 2006 and Canada isn't always as well-placed to see the entire event as it is this time. The next will be in 2019, but after that, there won't be another daytime Mercury transit viewable from Canada until 2049.

• Mercury transit a rare celestial event, but don't look directly at it: Bob McDonald

Not only are Mercury transits rare, but they're also some of the best opportunities to see the closest planet to the sun. Typically, it's tricky to observe even at night, because it's only ever visible near the horizon close to dawn or dusk, and you need to know where to look.

Mercury orbits the sun every 88 days, but isn't visible every time it passes between the Earth and the sun because Earth's and Mercury's orbits are tilted relative to each other. That means Mercury often appears above or below the sun when viewed from Earth.