By AMANDA JERMYN
Have you ever wanted a once-in-a-lifetime experience? If you missed the transit of Venus eight years ago, the one coming up on June 5 might just be your big chance. For most of us alive today, this is it because there won’t be another such event until December 2117, more than 105 years from now.
So what exactly is this rare phenomenon?
A transit of Venus occurs when the planet Venus passes directly between the sun and the Earth, becoming visible by obscuring a small part of the sun’s disk. During a transit, Venus is seen from Earth as a small black disk moving across the face of the sun.
This is similar to a solar eclipse, when the moon passes between the Earth and sun. Though Venus is almost four times the size of the moon it appears much smaller, and seems to cross the disk of the sun more slowly than the moon because it is much farther away from Earth.
Transits of Venus occur in pairs, eight years apart, separated by long gaps of more than a hundred years. The most recent occurred in June 2004, and the next, following this June’s transit, will occur 105.5 years from now. The only other planet whose transit across the sun can be seen from Earth is Mercury, with about 13 transits per century.
In 1627, Johannes Kepler was the first person to predict a transit of Venus, correctly forecasting the 1631 event. Though Kepler believed the next transit would only occur in 1761, Jeremiah Horrocks, an amateur astronomer in England, predicted another would take place in 1639.
Horrocks and his friend William Crabtree made the first known observation of a transit on Dec. 4, 1639. This enabled them to measure the diameter of Venus.
Subsequent transits were used to determine the distance from the Earth to the sun. Today one of the means of detecting exoplanets involves measuring the dimming of light that occurs as a planet moves in front of its star. So the 2004 transit provided an opportunity for scientists to hone their planet-hunting skills by studying the pattern of light dimming as Venus moved across the sun.
This year’s entire transit lasts just under seven hours. Due to the International Date Line, it occurs on June 5 in the western hemisphere and June 6 in the east, with the best view from the Pacific Ocean, including Hawaii, Alaska and the central Pacific islands.
North America will be able to see the start of it, until sunset, while south Asia, the Middle East and most of Europe will catch the last part, after sunrise. It will not be visible in West Africa and most of South America. In New England, the transit will begin at 6:03 p.m.
The safest way to view the transit is to project the image through a telescope or binoculars onto a screen. However it may be viewed directly through a telescope equipped with a solar filter or with the unaided eye, using a solar filter, special eclipse viewing glasses or Grade 14 welder’s glass.
One should never look directly at the sun as this may damage or destroy the cells of the retina, causing temporary or permanent loss of vision. Another safe way to observe the transit is to watch NASA’s live webcast from Mauna Kea in Hawaii. For more information on the webcast visit: http://sunearthday.nasa.gov/2012/transit/webcast.php
Here in Western Massachusetts, the Amherst Area Amateur Astronomers Association, together with the state Department of Conservation and Recreation and the Springfield Stars Club, will host a public Venus Transit observing program on Quabbin Hill at Quabbin Reservoir on June 5, starting at 5.30 p.m. Viewing of the transit begins at 6:03 p.m. and ends at sunset at 8:23 p.m. For more information, go online to www.venustransitquabbin.org
Enjoy this June’s transit of Venus! Next chance, December 2117!
Join the Springfield Stars Club on May 22 at 7:30 p.m. at the Springfield Science Museum for a round-table discussion on getting started in astronomy. Gain fresh insights into different aspects of astronomy, opening up new avenues for exploring the heavens. Refreshments will be served, and the public is welcome free of charge.