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Mercury’s winged messenger: Hugh Hunt organises planet viewing at Trinity

Visitors to Great Court are often surprised by its splendour and size. On 9 May 2016 there will be an added attraction. Tourists and students alike should be able to see the transit of Mercury across the sun (if the sun shines).

Hugh in Great Court © Paul Ashley
Hugh in Great Court © Paul Ashley

For this infrequent astronomical event – which happens roughly 13 times a century – an attempt will be made to view the transit beneath Queen’s Gate using a ‘special’ Mercury viewing device. ‘Actually, it’s all quite low tech,’ says Dr Hugh Hunt, Master of Planetary Ceremonies on Monday or, more properly, Reader in Engineering Dynamics and Vibration at Cambridge, and a Fellow of Trinity.

All you need is a small mirror to reflect the sun onto a screen in a dark room. It’s very simple, and it’s the perfect technique for viewing a solar eclipse. But to see Mercury the mirror needs to be very small, about the size of a pea, and it has to be held very still using a tripod.

Dr Hunt is known for recreating engineering history for documentaries watched by millions worldwide, from Barnes Wallis’ ‘bouncing bomb’ and Hitler’s ‘supergun’, to crafting the Colditz escape glider and helping motorcyclist Guy Martin break a speed record.

On 9 May, Dr Hunt’s focus will be on heavenly sights – brought down to earth via his reflected pinhole device and two ordinary telescopes as back-up.

The shadowy disc of the planet Mercury will begin to traverse the sun at precisely 12.12pm, taking several hours to pass across the sun’s disc and departing at 7.42pm. It will be the first time Mercury has transited the sun since 2006. Mercury is the smallest and fastest planet in the solar system, and it is the closest to the sun.

Planetary passages across the face of the sun are relatively rare – only the transits of Mercury and Venus can be seen from Earth. Dr Hunt explains:

A transit is just like a solar eclipse when the moon obstructs the sun, and even though the planets are much bigger than the moon they are so far away from us that they appear as small dots on the disc of the sun. The orbits of Mercury, Venus and the Earth are slightly inclined to each other – a bit like a pair of intersecting frisbees. That means that the planets don’t always line up perfectly in front of the sun.

Venus' silhouette against the sun © Hinode JAXA/NASA/PPARC
Venus’ silhouette against the sun © Hinode JAXA/NASA/PPARC

Venus transits are especially rare, occurring in pairs once a century, says Dr Hunt. He arranged a successful observation at Trinity of Venus’ journey in 2004 – there won’t be another one here until December 2125.

Those wishing to view Mercury’s transit on Monday should head to outside B2 Great Court where telescopes belonging to Trinity Fellow, Dr Richard Serjeantson, and Dr Tim Cutts, of the Sanger Institute, will be set up from noon. Dr Hunt will be present with his viewing device between noon and 2pm, and Lord Rees, the Astronomer Royal and former Master of Trinity, will also drop by.

‘We’re all set – all we need is a sunny day on Monday,’ said Dr Hunt, ‘and the weather is looking good!’

The Mercury viewing will take place noon-2pm on Monday 9 May if the sun shines. Visitors are welcome from 11.45am, free of charge.  Please remember, don’t look directly at the sun as it can damage your eyes.

Regular visiting rules and fees to enter the College will apply from 2pm.

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