A Transit of Venus DIY parallax kit

I've been wondering what the parallax effect in a Transit of Venus actually looks like. I know the 18th century astronomers used it to measure the solar system, because it says so in books. (See my post of June 6th The Transit of Venus in history which includes some good links). But just how pronounced is this parallax effect? Can anyone see it or is it miniscule?  Well, see for yourself ...

Here's a pair of computer generated images of the transit that happened a fortnight ago. 

Transit of Venus, 6 June 2012, 02:00 UT from Capetown

Transit of Venus, 6 June 2012, 02:00 UT from Cork

They show the transit at the same instant, 2am Universal Time.  One from Cork and the other from Capetown.  The pronounced black dot is Venus. The grey dots are sunspots. There is a small but quite definite difference in where Venus appears on the Sun’s disc. The effect is much too small to detect when you view these two images together on the screen. But you can see it very clearly if you flick between them.

Try it! It's a bit a of do-it-yourself job I'm afraid, and here's my suggestion how to go about it.

Create a new folder on your computer’s desktop and save each image into it.[1] Then click on one of the images to view it …  this will open your computer’s viewer software … now click the right arrow key to view the other image ... by repeatedly clicking the right arrow, you will see Venus shifting up and down. That’s parallax. 

Venus seen from Capetown appears higher up (further north) on the Sun’s disc than Venus seen from Cork.  

In the diagramme, A is the apparent position of Venus viewed from Capetown, and B is the apparent position of Venus viewed from Cork. (The diagramme hugely exaggerates the AB distance. Strictly speaking the Earth should be a small dot like Venus.)

Seeing Venus wobble as you flick between the two images, helped me to appreciate what Edmond Halley was banging on about when in 1716, he instructed the next generation of astronomers: go to the ends of the Earth to detect the parallax in the 1761 Transit of Venus, and use this to measure the solar system.  I won't go into how, as it involved trigonometry.

That, and some additional notes and links, are in this pdf file.

Thanks to Tony Jackson and Terry Moseley for help putting this together.

[1] In case you need instructions for saving the two images, here goes for Windows users. I assume you’ve already created a new folder on your computer’s desktop called Venus. Now hover over one of the above images, right click, and choose the menu option Save Image As. Save it into the Venus folder. Do the same for the other image. Your Venus folder now contains two images and you can flick between them.

Libraries without money better than money without libraries

Just seen a rather good libraries slogan, pity it's a bit long for a placard ...

Libraries will get you through times of no money better than money will get you through times of no libraries

Library campaigners with placards outside the high court in December 2011 [1]

Attributed to Anne Herbert, an American writer, born 1952, of whom I know nothing.  It seems she derived it from a quote of Gilbert Shelton (of whom I also know nothing): "Dope will get you through times of no money better than money will get you through times of no dope."

Another of her pronouncements is:  "Practice random kindness and senseless acts of beauty."

UK Library campaigning links:

    Voices For The Library  

    UNISON libraries campaign  

    Save Our Libraries campaign, one year on (Guardian books blog, Jan 2012)

[1] The high court protesters were from Brent, in an unsuccessful bid to obtain a judicial review of closures. (Photo: Guardian) 

The Transit of Venus in history

Watched today's transit of Venue 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 28th 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.

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:

http://www.youtube.com/watch?v=-nXv9YvkNyA&feature=relmfu

# The transit from the International Space Station:
http://www.youtube.com/watch?v=w5Lx4fC42KI&feature=relmfu

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

Judi Dench reads "Love is not love, which alters when it alteration finds"

     Let me not to the marriage of true minds
     Admit impediments. Love is not love
     Which alters when it alteration finds,
     Or bends with the remover to remove:
     O no! it is an ever-fixed mark
     That looks on tempests and is never shaken;
     It is the star to every wandering bark,
     Whose worth's unknown, although his height be taken.
     Love's not Time's fool, though rosy lips and cheeks
     Within his bending sickle's compass come:
     Love alters not with his brief hours and weeks,
     But bears it out even to the edge of doom.
        If this be error and upon me proved,
        I never writ, nor no man ever loved .

                   Sonnet 116

Listen to Judi Dench reading this

It seems Judi Dench remarked to the BBC’s James Naughtie that she liked to read a Shakespeare sonnet every day, so he asked her to recite just one. She obliged with sonnet 116.  Apparently this happened impromptu on 23rd May at a Royal Academy party marking the contribution of the creative arts in Britain during the last 60 years, to celebrate the Diamond Jubilee.

The first ever Transit of Venus - is this picture right?

"The Founder of English Astronomy", a painting by Eyre Crowe, 1891

I hope someone can tell me exactly what is going on in this 1891 painting, where the artist Eyre Crowe imagines Jeremiah Horrocks at the moment he witnessed the 1639 Transit of Venus.  What an evocative name. The goddess of love, and the brief and transitory nature of existence. The next one is in 6 days time on 5th or 6th June (depending on where you are [1]). In Ireland it's at dawn on Wednesday June 6th, and only the last few minutes will be seen, just as the Sun rises. And the next after that will be December 11, 2117 (a Saturday). [2]

In the painting Horrocks is projecting the image of the Sun, with Venus a small dark spot crossing it, on to a piece of card, on which he marks Venus’s trajectory.  

The 2004 transit (Wikipedia)

The event depicted is taking place late in the afternoon of 4 December 1639. Does the horizontal alignment of the telescope imply that the Sun is just about to set? Or am I trying to over-interpret Eyre’s painting? Perhaps he didn't know much about astronomy? I've seen it said that Horrocks actually used a camera obscura for his observation [3].

If the painting is right, then has Horrocks set up some arrangement of mirrors not shown?  How, I wonder, did he keep the telescope focussed on the piece of card throughout the transit, as the Sun and Venus declined in the sky?  And what is the contraption on the middle of the room?  

Horrocks witnessed the transit for about half an hour from 3.15 till sunset which might have been about 3.45 I suppose.  His prediction of when the transit would occur was accurate to (I think) a few minutes, but distrusting his calculations, he had been checking on the Sun continually, whenever free of clouds, for the previous 24 hours. Then just when the transit began, he was called away on urgent business (unspecified, but maybe as a clergyman he had to conduct a church service) so missed the beginning of it.

All this is in June’s edition of History Today which I saw in the public library in Cork but sadly don't have to hand as I write this. This link shows the first few paragraphs only.

Horrocks was the only person to predict the 1639 Transit, and he and his friend William Crabtree were the only two people to observe and record it. Horrocks was just 21 at the time, and died two years later. What a loss to science.  In several books I've looked at, his name doesn't even appear in the index.

Measuring the solar system

Venus transits are big events in the history of science.  In 1761 and 1769, astronomers undertook extraordinary expeditions to far-flung locations in the first global scientific collaboration.  I can recommend a Nature podcast on this. [4]

They were hoping to use their observations to calculate the size of the solar system. You can use a Transit of Venus to do this by comparing observations from widely different latitudes on Earth, and using the principle of parallax, trigonometry, and Kepler’s laws of planetary motion, which tell you the relative (though not absolute) distances of each planet from the Sun.

The June 2012 transit will help scientists to refine techniques to be used in the search for exoplanets, some of which are detected when they transit their stars.

[1] Worldwide map issued by NASA showing regions where the 2012 Transit is visible from, and when.

[2] The recurrence pattern is gaps of:  8 years, 121 years, 8 years, 105 years.

[3] John North, Fontana History of Astronomy and Cosmology (1994), p 349.

[4] Chasing Venus : Nature Podcast Extra (16 minutes).  Nature is one of the foremost scientific journals. Subscribe to their podcast and hear scientists talking to scientists.  As a taster try the episode of 26 January 2012, available on this page: hunting for 2,500 year old shipwrecks off the coast of Crete, insights into Alzheimer's from reprogrammed cells, and a research tool called 'primitive facebook' with hunter gatherers in southern Africa.

Why I'm voting No in the Irish austerity referendum

Socialist Party Vote No poster

To be honest it's only a gesture but gestures do matter. We’ve all heard the slogan a No vote is a vote against austerity. In itself that slogan sounds naïve - as the parties supporting a Yes have been quick to point out.

So a No vote is empty without a commitment to an ongoing campaign against austerity, and an expression of solidarity with the people of Greece. I'm afraid I'm too old and washed up to do a lot of campaigning these days but at least I'm supporting to the no household charge campaign. 

Incidentally the word austerity is much misused by politicians of the right, and most us have unwittingly fallen in with them. The original age of austerity was postwar Britain.  But the 1945 Labour government set up the welfare state and the NHS.  Look it up in a dictionary and you'll find austerity means the trait of great self-denial especially refraining from worldly pleasures.  But today austerity is being imposed because men in suits say that it’s necessary to satisfy the invisible gods of the financial markets, and it's used for a package of measures that increase inequality (already on the rise throughout the world for the past 30 years) and impacts mainly on the poor, and the people for whom worldly pleasures are already hard to come by.

The Irish referendum is to change the constitution to allow the government to sign up to the European Fiscal Stability Treaty, which will impose penalties on any government that runs a deficit budget.  It's supported by Fine Gael, Labour (the coalition parties) and Fianna Fáil, and opposed by the United Left Alliance and Sinn Fein. The vote is tomorrow.

A final point, there's no doubt a raft of new cutbacks and tax hikes has already been prepared, but will not be announced until after the referendum. The government got a fright from the backlash against the household charge, and you can be sure it is deliberately suppressing news.