What's a Transit?

@Julien asked how he could see June's Venus transit, but before I get onto that I thought it'd be a good idea to make sure everyone knows what a 'transit' actually is.

A photograph taken of the 2004 Venus transit by
Gestrgangleri using special equipment so as not to
destroy his telescope or melt his own retina.
Space is made up of all sorts of things, such as planets, stars, moons and the like, whirling around each other. Sometimes, a few of these things line up for a brief time. When one object appears, from the point of view of an observer, to move across the face of another one, this is called a transit.

When the Moon passes in front of the Sun, we call it an eclipse. When it blocks our view of the Sun completely, we call it a total eclipse. The general term for one object passing in front of another and blocking our view of it completely is an occultation. This can only happen if the closer object appears to be the same size in the sky or larger than the background object. If the object doing the passing appears too small to block the more distant object out completely, we call it a transit.

During sunrise on the morning of June 6th* 2012 Venus will appear to cross the face of the Sun. The last time this happened was in 2004- I remember watching Patrick Moore talking about it on the TV in my bedroom in my student house. The next time this happens will be in 2117, which means, unless there are some significant and unprecedented advances in medicine or you discover a magic door, you won't be around to see it.

I'll say at this point that, given that this is a transit of Venus across the face of the Sun, you really shouldn't be looking at it with your naked eye. Let me put that more strongly: do not try to view the event with your naked eye: if you look directly at the Sun for whatever reason and at whichever time, it stands a very good chance of being the last thing you'll ever see, ever. At all. So don't do it.

So how do I see next month's Venus transit safely?

If you're reading this blog then you probably find the idea of rare astronomical events quite exciting, and given that this is the last chance of your lifetime, then you'll want to have a good go at viewing it. But how?

That's for the next post.

Watch this space! But remember, DO NOT LOOK DIRECTLY AT THE SUN. Ever.

* As viewed from the UK, Europe, Asia and North-East Africa - America will need to view as the sun sets on the 5th.


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