Just as the transit of Venus causes a slight dimming of the Sun's light, so an exoplanet reveals its presence when it transits a distant star. That drop in light provides key data about an exoplanet's size and orbit. However, scientists want to build orbiting observatories that will study tiny changes in the light of a star as it passes through the atmosphere of an orbiting exoplanet.
These changes will allow them to assess the composition of that exoplanet's atmosphere and make estimates of surface conditions. Does it have a thick crushing atmosphere or does it possess only thin levels of gas and is therefore unlikely to support life?
Does it contain oxygen or does it have poisonous gases? And that is where the transit of Venus should provide crucial data, says Crisp. Thanks to probes like Europe's Venus Express, we have precise knowledge about its atmosphere and surface. By studying Venus as if it was an exoplanet we will know how good are our techniques and how much they need to be refined.
A whole network of astronomers will be studying the transit of Venus for this reason. A transit of Venus occurs when the planet and Earth, whose paths round the Sun tilt at slightly different angles, line up exactly where their orbits cross. This occurs only four times every years, in pairs separated by eight years. Only six transits of Venus are known to have been observed though claims are made for earlier observations by Persian astronomers with the last, in , watched by millions who used telescopes to project images of the Sun's disc and the dot of Venus on to cards or electronic monitors.
After this year's, the next will be in and then When the previous pair occurred, Queen Victoria was on the throne. The first transit of Venus was predicted by Johannes Kepler who calculated one would occur in However, this was not visible from Europe. The next one occurred on 4 December when Jeremiah Horrocks became the first person to watch a transit of Venus when he shone an image of the Sun on to a piece of white card and was rewarded, around 3. From his observations, Horrocks used triangulation techniques to make the best estimate then attempted for the size of Venus and the distance of the Earth from the Sun, though in the latter case he was still out by many millions of miles.
Ames' Batalha kicked things off with a standing-room-only talk at p. As hundreds of people listened inside Ames' Exploration Center, Batalha explained why planetary transits intrigued astronomers over the centuries— and why they're still important today.
NASA's Kepler space telescope uses transits to detect alien worlds, for example, flagging the tiny brightness dips caused when exoplanets cross their stars from the telescope's perspective.
When Batalha finished, the focus shifted to the live NASA webcast of the transit, which began playing on the Exploration Center's huge screen. Moans and murmurs ran through the crowd when the feed was lost around 3 p. PT, just as Venus was getting set to touch the solar disk for the first time.
But an appreciative and reverent silence set in when the video was restored and Venus appeared on the sun's limb. The crowds were big outside in the parking lot, too, where several dozen amateur astronomers had set up specially filtered telescopes and binoculars. It was a perfect day for viewing, sunny and clear, and hundreds of onlookers queued up to see the spectacular sky show.
One such skywatcher was 6-year-old Natalie Buckley, who came to the event with her family. Natalie said she saw Venus and sunspots through the various telescopes, an experience she described as "cool and weird.
Most of the attendees were doubtless locals, drawn to Ames from various spots around the Bay Area. But two hardcore skywatchers came all the way from Spain. The two came to California because they could see most of the transit from here, and because they figured the weather would cooperate. He saw the Venus transit in Spain, but with relatively rudimentary equipment. He and Gonzalez Pena brought a bunch of high-tech, high-performance gear to California with them to document this transit, the last one they'll ever see.
Lauren Aldorody, 17, said there was just something extra special about watching Venus pass in front of the sun that sets it apart from other celestial events. The "Gore-y" Details. This close-up view of Saturn's moon Janus shows what appear to be two large craters near the boundary between day and night.
The left side of the moon is lit feebly by reflected light from Saturn. Janus: God of Beginnings. At upper left, material from the rim of a fresher crater appears to have slumped into its neighbor. Cassini surveys a bright landscape coated by dark material on Iapetus.
This image shows terrain in the transition region between the moon's dark leading hemisphere and its bright trailing hemispher Coated Craters. Great Dark Spot. A close-up view of the Keeler Gap, which is near the outer edge of Saturn's main rings, shows in great detail just how much the moon Daphnis affects the edges of the gap. Waving Goodbye. Lit by reflected light from Saturn, Enceladus appears to hover above the gleaming rings, its well-defined ice particle jets spraying a continuous hail of tiny ice grains.
Brilliant Ice Dust. The Cassini spacecraft looks down on the north pole of Mimas and sees the moon's cratered trailing hemisphere.
The moon's north pole lies on the terminator about a quarter of the way inward from t Trailing Hemisphere Craters. Enhanced color image of the region surrounding the young impact crater Pwyll on Jupiter's moon Europa. Pwyll Crater on Europa.
This image from NASA's Dawn spacecraft show a slightly curved chain of small craters in the bottom half of the image. This chain is located on the floor of asteroid Vesta's large south-polar impact Curved Chain of Small Craters. This beautiful look at Saturn's south polar atmosphere shows the hurricane-like polar storm swirling there.
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