Venus rapid transit, first observer, mind your eyes
What is the transit of Venus? Is it anything like the Bay Area Rapid Transit?
(Jay) Seattle, Washington
Venusí 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 ó and, silhouetted, moves like a black dot across the Sunís brilliant disk.
The transit corresponds to a solar eclipse except Venus is so far away that it
will blot only 0.1% of the Sunís surface, compared with the Moonís blocking of
the entire Sun.
The next transit will be soon: on Tuesday June 8.
Space Flight Center: 2004 transit of Venus by Fred Espenak and Jay Anderson
See the transit ó broadcast live from NASAís site, hosted by Sten Odenwald
Who was the first person to see Venus cross the Sun? (Mauna Jean, London,
"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."
ó U.S. Naval Observatory astronomer William Harkness,
Jeremiah Horrocks watching the transit of Venus in 1639
for a larger image. [Painting by Eyre Crowe (1824 - 1910) Smithsonian
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 wouldnít 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
didnít 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 Sunís
Institution Library: Chasing Venus, 1631 - 2004
Mind your eyes
Q: Iíd 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 Sunís 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?
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 ó 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. Thatís our last
chance. The next one after that isnít until Dec. 11, 2117 ó 105 years down the
Safe viewing. Since Venus is so
distant and itís 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 donít 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
& Telescope: Solar filter suppliers
Paper Optics, Inc.: Eclipse glasses
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)