Cayman Islands residents and visitors will have the extremely rare chance to watch the planet Venus transit across the face of the Sun in the late afternoon of Tuesday 5 June. This opportunity will not occur again for 105 years.

In honour of the 21st anniversary of the Cayman Islands Astronomical Society (CIAS), the public is invited to safely view this momentous event from the rooftop of 62 Forum Lane, Camana Bay from 5 to 7pm. There will be a small astronomy exhibition and a number of CIAS telescopes on hand, fitted with specialist solar filters. Solar viewing glasses will be provided.

On Tuesday 5 June, it will take Venus over 6 hours to make its transit across the Sun; the planet will appear as a ‘dot’ which will cross its surface. School children will enjoy watching CIAS members conduct a worldwide experiment to time the two points when Venus starts and finishes its journey across the Sun. These two moments in time are not easy to measure; the second of which produces a famous ‘tear drop’ effect, when Venus is at the edge of the Sun’s disk.

Transits of Venus across the Sun were once considered to be of the greatest importance to science, and huge efforts were expended trying to record them. After a first attempt to predict th event by Johannes Kepler in 1631, it was first observed eight years later by Jeremiah Horrocks.

This enabled, for the first time, accurate measurements in astronomical distances to be made, and in particular the distance from the Earth to the Sun. This important ‘yard stick’ is still called the ‘Astronomical Unit’.

Each successive transit attracted world-wide expeditions, including the famous expedition of British explorer James Cook, who was dispatched to Tahiti in 1769 to record the times of this phenomenon. The primary purpose of the expedition was to obtain measurements that could be used to calculate more accurately the distance of Venus from the Sun. If this could be achieved, then the distances of the other planets could be worked out, based on their orbits. Today, transits are still considered to be important, and recent new techniques will be tested to search for planets in other solar systems.

If you are thinking of observing the Sun from elsewhere, CIAS recommends waiting until close to sunset, when the sun is low on the horizon and safer to observe. Please note: observing the Sun directly (even through a telescope or camera lens) can seriously damage your eyesight – and your camera lens.

Transits of Venus occur in pairs separated by eight years. Each pair is in turn separated by an alternating interval of 105.5 and 121.5 years, making a cycle of 243 years. The last transit of Venus was in June 2004, where modern instruments gave the best views ever and the next transit of Venus will not be seen from Earth until 2117.

Join the Cayman Islands Astronomical Society for this once in a lifetime event – just don’t think about how old your children’s children will be in 2117!

For more information, contact [email protected] or visit Facebook.com/Cayman Islands Astronomical Society.