Wednesday, June 6, 2012

The Transit of Venus in history

Watched it on the web. Many crashes. Slightly disappointing. No, it's the history that excites me. There's a heap of stuff on the web about how the Transit of Venus was used for measuring the heavens in the 18th century.  Here's the best I found.  First,  Stuart Clark on the Guardian science blog.  He says that in scale and ambition, plans to record the transit of Venus were the 18th century equivalent of the Large Hadron Collider.

There's a book just brought out by the historian Andrea Wulf: Chasing Venus: The Race to Measure the Heavens, which documents the collaboration required to observe and track the 1761 and 1769 transits.

She discussed the book on the Guardian Science Weekly podcast of 25th May.

And a few days ago she gave a lecture to the Royal Society. This link allows you to see the video, or download the audio.

The maths: how the Transit of Venus tells us our distance from the Sun

Imagine two different people, one on each pole of the Earth, viewing the transit of Venus. The person on the North pole sees Venus following one path across the Sun. The person on the South pole sees Venus follow a slightly higher path, one that's shifted a little to the north. Because we see the Sun as a circle, these two different paths will have different lengths. Halley proposed that an easy way to measure the difference between the lengths of these two paths would be to time the transits, using the four phases of the transit — the first, second, third, and fourth contacts — as indicators. With the two different paths known, the distance between the Earth and the Sun can be pretty easily calculated using trigonometry and Kepler's third law of planetary motion.

If you want a bit more, including just a few equations,  this explainer is for you, it's from the Exploratorium museum in San Francisco.

Guardian Science blog: Transit of Venus as it happened

The Guardian, as we used to say, and I still do, is definitely where it's at. Trawl through their live blog, dead now of course, for snippets of history, images of the transit, and comments as it occurred.

Edmond Halley, portrait by Thomas Murray, c. 1687 (detail)
This is Edmond Halley, the English astronomer and geophysicist.  A true giant. From beyond the grave, he it was who launched the world expeditions to view the transit. In 1716, he instructed the next generation of astronomers: This is what you have to do. Fifty years from now, in 1761, there will be a Transit of Venus, and you all have to work together. It's all in the Guardian blog, scroll down for this image.

Tuesday, June 5, 2012

The Transit of Venus 10 hours from now

An astronomer points to Venus on a projection
from the solar telescope at the Astrophysical
Institute of Potsdam in Germany on 8 June 2004.
Photograph: Sven Kaestnerj/AP
The transit starts at tonight at 22.04 UTC [1] (that’s 11.04pm BST, 4 minutes after midnight Central European Time, and if you're in the US, 6.04pm EDT). 

Venus takes nearly seven hours to cross the face of the sun.

From most of Europe the transit will be in progress at sunrise on Wednesday, and the last hour or more of it will be visible. Just about the worst place to see it is in County Cork, Ireland.  Only a few minutes if you're lucky. Despite the odds, a number of Cork Astronomy Club members are having a crack at it. None of us will ever see this again.

There are more websites than enough devoted to this event but here is my small selection of the most useful:

[subsequent note: have shortened this by deleting links that disappointed ]

# For beginners, a Q & A from The Guardian

And two NASA ScienceCasts. 

# An intro to the Transit of Venus and the history:

# The transit from the International Space Station:

[1] Coordinated Universal Time (UTC) is what I used to call Greenwich Mean Time