VOA标准英语2012--NASA Satellite Offers Astonishing View of Venus Transit（在线收听）

NASA Satellite Offers Astonishing View of Venus Transit

Skygazers massed outside the Smithsonian National Air and Space Museum in the U.S capital, eager to see the rare transit of Venus.

The museum offered telescopes. People donned special protective glasses so they could peer directly at the Sun.

But the sky offered cloud cover instead of a view of Earth's neighbor appearing in silhouette against the Sun.

One observer, Colin Davies, first heard of the astronomical event only hours before the transit began.

"Ready to see whatever there is to be seen," said Davies, brandishing binoculars that are not recommended for solar viewing. "I have my umbrella, planning for all weather, and I have my fold-away chair because I'm here for the long haul."

For Davies and his wife, Mary Ellen Lane, there was nothing to see but clouds, which "deeply disappointed" Davies. 

Skywatchers in other parts of the world had a bit more luck. Technically, this transit of Venus was visible from all seven continents. Observers in Australia had some degree of success. 

"You could just see a faint orange dot and then there was a little black dot on it," described a boy in Sydney. "You could only just half-see it, but yes."

Yet, the view from space was pretty phenomenal.

A NASA spacecraft that takes images of the Sun provided an ultra high-definition view of the transit of Venus. The Solar Dynamics Observatory collected the images in many wavelengths over the course of the planet's six-hour crossing. In some images, the Sun is active and flaring, with the darker circle of Venus passing in front of it. In others, Venus appears as a small black dot against a monochromatic orange disc of the Sun.

Transits of Venus have happened only seven times since the phenomenon was first observed with a telescope in 1639. They've occurred only twice since the invention of the television and only once since the Solar Dynamics Observatory was launched into space.

Transits of Venus occur in pairs that are eight years apart, but the pairs are separated by more than a century.

The predictability held a key for astronomers centuries ago, and the transits continue to provide learning opportunities, says Jim Zimbelman, a planetary geologist at the Air and Space Museum in Washington.

"Historically, the interest in transits started when we wanted to understand how big the solar system was and there were complications, maybe introduced by the atmosphere of Venus," explained Zimbelman. "Well, today's transit can actually be a test run for 'can we detect atmospheres around planets orbiting other stars?' Who would have believed in just a few hundred years we would have advanced our ability to ask science questions like that?"

In Washington, the question many people asked was whether the Sun was ever going to come out from behind the clouds.

Those who missed the chance to see the Transit of Venus this year missed the chance of a lifetime. The next one isn't until 2117.