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

The planet Mercury will pass in front of the sun on Monday in a rare event called a transit. It will be visible across Canada during the day, but don't look directly at the sun with your eyes to see it.

Mercury is the closest planet to the sun and also the smallest in our solar system, just slightly larger than our moon.

It even looks like our moon, with a barren, rocky surface strewn with craters.

The speedy little planet is hard to spot in telescopes because it is always close to the brilliance of the sun. As a result of that close proximity to the solar inferno, only two spacecraft have journeyed there. That's why a transit is a convenient and safe way to study the planet from the safety of Earth.

Thanks to an alignment of the sun, Mercury and the Earth, which only happens about a dozen times per century, astronomers will track Mercury's motion as it crosses in front of the solar disc to get precise measurements of its orbital speed, as well as the nature of its thin atmosphere.

The surface of Mercury gets blasted so hard by solar radiation that the ground heats up to 427°C during the day, burning sodium atoms right off into space.

Mercury 2006 transit

The path of Mercury during its 2006 transit is shown in this composite image created from observations by the Solar and Heliospheric Observatory. (SOHO/NASA)

This gives the planet a long, thin, gaseous tail like a comet. That tail should become visible to some instruments when it appears against the bright face of the sun, giving scientists a chance to study its composition.

For the rest of us, the transit will begin at 7:16 a.m. ET and be visible for seven hours, so for people in the West, it will already be in progress when the sun rises.

But do not try to see it with the naked eye.

The sun is far too bright to look at any time, so don't risk blinding yourself trying to see a little dot. You won't see anything anyway. And sunglasses will not protect you.

But there are several options to view the event safely. The Royal Astronomical Society of Canada will be setting up telescopes with proper solar filters on them on the grounds of Parliament Hill in Ottawa, as well as in many communities across the country. Check for notices in your area.

Make your own projector

You can also make a projector out of a pair of binoculars. But again, do not look through the binoculars directly at the sun.

The absolute safest way to see it is to watch it live via online broadcasts from professional observatories on the ground and in space. Two good sites are here and here.      

Most people have never seen Mercury because it barely peeks above the horizon — either just after sunset or just before sunrise. To see it exposed in the middle of the day is a rare treat.

But if you miss it, the next transit opportunity will not be until 2019.

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