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Venus to transit sun in rare display
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May 18, 2012 |
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For a full
size image of map showing transit times,
click the map pictured. |
On June 5, 2012, Venus will pass across the face
of the sun, producing a silhouette that no one
alive today will likely see again.
Transits of Venus are very rare, coming in pairs
separated by more than a hundred years. This
June's transit, the bookend of a 2004-2012 pair,
won't be repeated until the year 2117.
Fortunately, the event is widely visible, to
include North Idaho if the weather cooperates.
Observers on seven continents, even a sliver of
Antarctica, will be in position to see it.
The nearly seven-hour transit begins at 3:09
p.m. Pacific Daylight Time (22:09 UT).
The timing favors observers in the mid-Pacific,
where the sun is high overhead during the
crossing. In the USA, the transit will at its
best around sunset. That's good, too. Creative
photographers will have a field day imaging the
swollen red sun "punctured" by the circular disk
of Venus.
Observing tip: Do not stare at the sun. Venus
covers too little of the solar disk to block the
blinding glare. Instead, use some type of
projection technique or a solar filter. A #14
welder's glass is a good choice. Many astronomy
clubs will have solar telescopes set up to
observe the event; contact your local club for
details.
Transits of Venus first gained worldwide
attention in the 18th century. In those days,
the size of the solar system was one of the
biggest mysteries of science. The relative
spacing of planets was known, but not their
absolute distances. How many miles would you
have to travel to reach another world? The
answer was as mysterious then as the nature of
dark energy is now.
Venus was the key, according to astronomer Sir
Edmund Halley. He realized that by observing
transits from widely-spaced locations on Earth,
it should be possible to triangulate the
distance to Venus using the principles of
parallax.
The idea galvanized scientists who set off on
expeditions around the world to view a pair of
transits in the 1760s. The great explorer James
Cook himself was dispatched to observe one from
Tahiti, a place as alien to 18th-century
Europeans as the Moon or Mars might seem to us
now.
Some historians have called the international
effort the "the Apollo program of the 18th
century."
In retrospect, the experiment falls into the
category of things that sound better than they
actually are. Bad weather, primitive optics, and
the natural "fuzziness" of Venus’s atmosphere
prevented those early observers from gathering
the data they needed.
Proper timing of a transit would have to wait
for the invention of photography in the century
after Cook’s voyage. In the late 1800s,
astronomers armed with cameras finally measured
the size of the Solar System as Edmund Halley
had suggested.
This year’s transit is the second of an 8-year
pair.
Anticipation was high in June 2004 as Venus
approached the sun. No one alive at the time had
seen a Transit of Venus with their own eyes, and
the hand-drawn sketches and grainy photos of
previous centuries scarcely prepared them for
what was about to happen.
Modern solar telescopes captured unprecedented
view of Venus’s atmosphere backlit by solar
fire. They saw Venus transiting the sun’s
ghostly corona, and gliding past magnetic
filaments big enough to swallow the planet
whole. One photographer even caught a spaceship,
the International Space Station, transiting the
sun alongside Venus.
2012 should be even better as cameras and solar
telescopes have improved. Moreover, NASA’s Solar
Dynamics Observatory is going to be watching
too. SDO will produce Hubble-quality images of
this rare event.
For more news and information as the date of
transit approaches, stay tuned to
http://science.nasa.gov. |
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