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Venus rapid transit, first observer, mind your eyes

Q: What is the transit of Venus? Is it anything like the Bay Area Rapid Transit? (Jay) Seattle, Washington

Venus’ transit will look much like this 1973 Mercury transit. [© 1973 by Fred Espenak, www.MrEclipse.com. Used with permission.]

A: During its rare transit, Venus passes between Earth and the Sun — and, silhouetted, moves like a black dot across the Sun’s brilliant disk. The transit corresponds to a solar eclipse except Venus is so far away that it will blot only 0.1% of the Sun’s surface, compared with the Moon’s blocking of the entire Sun.

The next transit will be soon: on Tuesday June 8.

Further Reading:

NASA/Goddard Space Flight Center: 2004 transit of Venus by Fred Espenak and Jay Anderson

NASA: See the transit — broadcast live from NASA’s site, hosted by Sten Odenwald

First observer

Q: Who was the first person to see Venus cross the Sun? (Mauna Jean, London, Ontario)

"We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth, and the June flowers are blooming in 2004.... What will be the state of science when the next transit season arrives God only knows." — U.S. Naval Observatory astronomer William Harkness, 1882

Jeremiah Horrocks watching the transit of Venus in 1639 Click here for a larger image. [Painting by Eyre Crowe (1824 - 1910) Smithsonian Institution Libraries]

A: On Dec. 4, 1639 a gifted English astronomer and mathematician, Jeremiah Horrocks, and his friend, William Crabtree, were the first recorded watchers of a Venus transit. Only a month before the event, Horrocks managed to predict the event and was the first to do so. (Kepler thought the next Venus transit wouldn’t occur until the following century.)

A little before the transit began, Horrocks set up his telescope in his home north of Liverpool. He checked the Sun frequently since he didn’t know exactly when Venus would start across. At 3:15 p.m., he saw Venus as a "spot of unusual magnitude and of a perfectly circular shape" on the Sun’s face.

Further Reading:

Smithsonian Institution Library: Chasing Venus, 1631 - 2004 

Mind your eyes

Q: I’d like to watch the transit. How can I without hurting my eyes? (Shirley, Florida, New York)

A: Your question is well advised. Venus will block only a tiny bit of the Sun’s light during its transit. This means that looking at the Sun then is "very dangerous" without appropriate equipment, says Robert Massey, astronomer at the Greenwich Royal Observatory. More about the right equipment soon but first: who can see it?

Like a solar eclipse, some Earthlings will not be able to view the transit directly. Those of us in the western US and Canada, and the tip of South America are out of luck. Almost all the rest of the world is more fortunate.

World map shows who sees what of the 2004 Venus transit across the Sun. Click here for a larger version.  [Fred Espenak, NASA]

On June 8, Easterners will see the Sun rise with the Venus black dot about 75% of the way across. The farther east you are, the longer your view of the transit: from Maine (2.5 hours) to Florida (1 hour). Europe, most of Africa, and most of Asia can see the whole thing — 6 hours. Australians, Indonesians, Philippinos, and Japanese will see the black dot start across the Sun but the Sun will set before they can see the whole passage.

West Coast watchers will see much of the next transit in 2012. Alaska, much of Australia and Asia will see the whole thing. That’s our last chance. The next one after that isn’t until Dec. 11, 2117 — 105 years down the road.

Safe viewing. Since Venus is so distant and it’s silhouette so correspondingly tiny, the best way to see it is with binoculars or a telescope. To do this safely, we need special solar filters (about $100). Please see Further Reading for suppliers. Unfortunately, everyone else is ordering filters now and the darn things take 4 to 6 weeks to arrive.

Whatever you do, though, "please don’t attempt to improvise filters as you could really damage your sight," says Massey.

We can use binoculars safely even without the special filters but we must not look at the Sun. Instead, "...project twin images of the Sun and Venus on a stiff piece of white cardboard held 3 to 5 feet behind the binoculars," recommends Fred Espenak, astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. We need to experiment a bit with how far away to hold the cardboard because the greater the distance the larger (but fainter) the image. "Never look directly through binoculars at the Sun unless the binoculars are fitted with special solar filters over their objective lens," Espenak cautions.

Another safe way to see the transit is to buy a pair of eclipse glasses. These "sun glasses" filter out 99.999 % of the ultraviolet and infrared rays of the Sun. The glasses only cost $0.85 each but the minimum order is for 25 pairs. So, an order buys extras for friends. American Paper Optics ships within 24 hours.

Finally, safest of all: even we Westerners can see the transit, live, on NASA’s website.

Further Reading:

Sky & Telescope: Solar filter suppliers

American Paper Optics, Inc.: Eclipse glasses

Norwegian Astronomical Association:  webcast will start at 12 a.m. EDT on 8 June 30 minutes before the transit starts and end at 7 a.m. EDT about 30 minutes after it ends  

(Answered June, 4 2004)