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Marlborough College
Oxford Astrophysics
Green Templeton College

'Someone has hole-punched the Sun'

The 2004 Transit of Venus, Tuesday 8th June

Getting Marlburians up at 6am had to be a major event ...and it was.

The weather was for once superb. The whips of cloud that had hung around in the East from about 4am were slowly clearing and the Sun was rising high enough for the telescope to start tracking it at 5.45am. A couple of pupils arrived at 5.30am having got the start time wrong (as in fact had the BBC Wiltshire webpage, until corrected). By 6am a crowd had started to gather and by 6.15am all eyes were on the Solar Scopes (projecting an image of the Solar disc) or peering through Eclipse shade filtered specs or scanning the Sun's disc through the 10" awaiting the arrival of Venus as predicted in 1631 and first viewed in 1639. This day hour and minute had been anticipated for so long...would it arrive? The first tiny sign of non even circumference of the Sun occurred visibly at 6hrs 20mins and 30 seconds, this was first contact and the excitement was palpable, here it was ready to make the 6 hour journey across the Sun visible form Marlborough last in 1882 (see diary excerpt) and not visible again for over 100 years from here. To be in a position to see all 4 contacts (see diagram) is even rarer and it will be the 24th Century before that happens in Marlborough.

As Jeremiah Horrocks the Englishman who at 22 found an error in the great Johanness Kepler's calculation that meant a transit would occur in 1639 not next in 1761, enabled him to witness the event first. His poem (see below) beautifully illustrates the passing of time and the legacy left to our ancestors to witness this event, itself highlighting the clockwork precision of the Solar System.

Our 'time' was entered in the European Southern Observatory's world-wide experiment (we were one of 760 Schools and 2000+ observers). Our measurement was the 3rd onto the internet and the precision was an awesome 99.83% accurate.

Second contact was also hard to judge, though the quality of our instrument and lenses meant that although the exact separation of the dot form the circumference was hard to see, there was no real black-dot effect (which had so altered the accuracy of early measurements, including those of James Cook (see drawing).

For this 'black dot' had inspired the 18th century Astronomers to depart on expeditions all over the globe to measure the times of contact and thus by trigonometry to find the distance to the Sun and hence set a scale to the Solar System. In 1761 the Seven years war meant that expeditions form England and France came under attack from each other and many lives and equipment were lost and measurements missed. With 1769 transit it was obvious that someone had to go south of the Equator in to largely uncharted waters. Maskelyn the Astronomer Royal was too important to risk, so his number 2 Charles Green was sent (he had successfully tested Harrison's Chronometer (ref: 'Longitude' by Dava Sobel) in the Caribbean. The navy however did not wish to risk their ship with an Astronomer in charge, so promoted Lieutenant James Cook to Captain and told him to take the Astronomers and their telescopes to the newly discovered island of Tahiti. They got there, stockaded themselves in ( to keep out inquisitive natives ) and successfully viewed the transit. The rest if history, James Cook sailed on and bumped into New Zealand and the Australia. But for the 'black dot' the Antipodes' discovery would have had to wait and indeed they might have been claimed by France or Spain.

As the dot separated from the limb, the Sun looked more and more if someone had simply taken a hole punch to it, the disc of Venus was so perfect and so black. For those who had watched the Transit of Mercury in May 2003, Venus was 5 times the size and much easier to see. The gathering crowds of pupils, staff (both teaching and non-teaching) there were mixed views, from the perspective of scale (Planets, including the Earth, really are very small) to the lack of dimming of sunlight to the simple view of the dot.... but all felt they were part of an historic moment.

At 8.30am the Observatory opened to the Public and a steady stream of people and then classes from Local Schools arrived to be all given the same introduction and ability to view by eye, then projected image and finally through the 10".

Eventually at 12 hours 04 minutes and 37 seconds Venus hit the other side of the Solar disc, more times were taken and the last group of visitors just caught the final moments and then it was gone, on its way, destined to cross again in December 2008, though only viewable from the USA or Pacific. The observatory emptied, only the debris of grass cuttings brought in on shoes and empty breakfast bags and plastic cups bore witness to the 400+ visitors (averaging more than 1 per minute). We were lucky, there will be other events, but I feel there will not be another like this in my lifetime.

From September 2004, CEB will be the first official Director of the Blackett Observatory and may be contacted via the College to arrange visits. Summer School courses also run at the Observatory

Addenda:

1) Horrocks' Poem

Oh! then farewell, thou beauteous queen!
Thy sway may soften natures yet untamed,
Whose breasts, bereft of the native fury,
Then shall learn the milder virtues.
We, with anxious mind, follow thy latest footsteps here,
And far as thought can carry us;
My labours now bedeck the monument for future times
Which thou at parting left us. Thy return
Posterity shall witness; years must roll away,
But then at length the splendid sight
Again shall greet our distant children's eyes.

Jeremiah Horrocks (1618-1641) Ref: ESO vt-2004 website

2) Diary entry

Wednesday, December 6th, 1882

"After Hall observed the transit of Venus several times through a smoked glass....." Ernest Firth (B1 1877-1884)

Thanks to T.Rogers, Archivist