Scientists Prepare for Rare Astronomical Event

By Patricia Reaney

Europe, the Middle East and much of Asia and Africa will offer prime viewing next month for an astronomical event that has not occurred for 122 years -- the transit of the planet Venus across the sun.

Weather permitting, for six hours on June 8 astronomers and the public will be able to see the planet named after the Roman goddess of love and beauty passing directly between Earth and the sun.

The event has been billed as a once in a lifetime experience because the last transit was on December 6, 1882 and the next one will not occur until June 6, 2012, but will not be visible in Britain and other parts of Europe.

"Something wonderful, something marvelous is happening on June 8th and will be witnessed and experienced by millions of people all over the world," Gordon Bromage, a professor of astronomy at England's University of Central Lancashire, told a news conference on Tuesday.

"It is an extremely rare astrological event."

The transit, when Venus will appear as an intense black dot about 1/30th the diameter of the sun, will be visible in the morning in Britain, most of Europe and Africa, later in the day in the Middle East and across Russia and India and later still in the Far East, which will get a limited view.

Scientists warn people not to look at the sun with the naked eye or through a telescope or camera because it can cause blindness. A solar filter or eclipse viewer should be used and for just very short periods.

During the transit, the orbits of Venus and the earth, which tilt at different angles, around the sun will line up exactly. It occurs four times in every 243 years. There are two December transits, eight years apart, and then 121.5 years later there are two June transits, also eight years apart. After another 105.5 years the cycle begins again.

"It is a very special period of six hours," said Bromage.

British astronomer Jeremiah Horrocks recorded the first transit of Venus across the sun in 1639.

The event is significant because it happens so rarely. Previous transits have also given scientists an opportunity to measure the scale of the universe and the distance from the Earth to the sun, which is called the astronomical unit (AU).

"Without that we couldn't measure any distances in the universe. Every other distances we measure...are all derived from the measurement of this basic yardstick -- the distance from the Earth to the sun," Bromage said.

Astronomers are also interested in the general principle of planet transits to hunt for extrasolar planetary systems.

It will allow scientists to study the famous "black drop" problem which makes timing the transits difficult. As the black disc of Venus appears on the sun it seems to have a dark neck, or become pear-shaped, for a short time. The opposite occurs when it leaves the sun.