The Transit of Venus

by Deb on June 4, 2012

Venus Transit

Photo of the 2004 transit by Jan Herold.

If your social media feeds are anything like mine, they are currently going crazy about the transit of Venus. I have emails, tweets, updates and more tweets reminding me that it’s the last time this century we’ll get to see it. So for those of you for whom this blog is your sole science reminder, I’m adding my 2c worth.

What

A transit of Venus is when Venus passes between us and the Sun. It is similar to an eclipse except the distance between the Earth and Venus makes it appear as a tiny dot travelling across the Sun. It’s a great way to get an idea of the relative size of the sun, given that Venus is roughly the same size as Earth.

When

Because Venus orbits inside Earth’s orbit, they line up relatively frequently. But usually Venus is above or below the plane of the Earth so we don’t see it. Transits occur in pairs 8 years apart, with long gaps over 100 years in between. There was a transit in 2004 and the next one won’t be until 2117, so this is almost certainly your last chance to see it.

It will be on June 5th/6th and the exact time depends on your location. In central Australia it starts at 7:45am and goes until 2:15pm, so there’s plenty of time to catch it. To find the times at your location, use this handy calculator.

Where

Most of the world is going to get some chance to see it, although not everyone will see the whole thing. This map tells you what you’ll see in your area.

transit map

How

DO NOT LOOK DIRECTLY AT THE SUN. You will burn your eyes and you won’t see anything anyway. View the transit in the same way as you would an eclipse, using a telescope, binoculars or pinhole camera to project the sun onto a screen. This is our setup:

Shade

Put a mask around the telescope to make it easier to see the image.

telescope

A lot of guessing and looking for landmarks gets the telescope in roughly the right direction, then move it until you see an image on a screen behind it.

sun

The sun and clouds projected on a paper screen, the shade makes it easier to see.

You can do the same using binoculars or even a couple of pieces of card.

Why

It’s interesting and unusual! Scientists are observing the transit for all sorts of reasons, by seeing how a known planet behaves crossing a known star it will help us detect and study exoplanets. It will also help us study Venus’ atmosphere and climatology, and it can help us calculate the distance from the earth to the sun.

This is important historically to Australians. Captain Cook was sent to Tahiti to observe the 1769 transit, and then search for the Great South Land. He was far from the first, or even the first European, to discover Australia, but his was the first organised expedition and led to British colonisation.

Extras

Depending on clouds I’ll be posting photos throughout the day here and Facebook and tweeting them through Instagram. Join in for my first live tweet science event :D

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