Thousands of would-be astronomers looked to the skies today hoping to catch a glimpse of the Transit of Venus.
Cloudy weather across much of New Zealand had threatened to ruin the rare event for many however the spectacle was still able to be seen through breaks in the cloud cover.
Venus began crossing between the Sun and Earth at around 10am and its silhouette was visible until 5pm.
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Transits of Venus happen in pairs, eight years apart, with more than a century between cycles. It will be another 105 years until Venus does this again.
At the Auckland Stardome and at Mt John Observatory in Tekapo, all eyes were on the sky.
"It's been just an incredibly cool experience to see this, it's extraordinary," said one would-be astronomer.
"I wouldn't have missed it, I looked at the weather this morning and I saw we had a gap in the clouds so yes, amazing," said another.
The spectacle is also an opportunity for astronomers to measure small dips in the sun's brightness, to map new planets beyond Earth's solar system.
"We can extrapolate that out to the stars that are in the night time skies and we can measure tiny dips in brightness and infer that there are planets orbiting around those stars, are we alone, that's the question we are asking," Astronomy Presenter Peter Felhofer told ONE News.
Scientists have been studying the event for centuries and in 1769 dozens of explorers were sent across the globe to record it.
One of those explorers was James Cook who was dispatched to Tahiti. It was on that expedition that he first discovered New Zealand.
Skywatchers on seven continents, including Antarctica, were able to see all or part of the transit. Even astronauts aboard the International Space Station joined in the spectacle.
"I've been planning this for a while," space station flight engineer Don Pettit said in a NASA interview. "I knew the transit of Venus would occur during my rotation, so I brought a solar filter with me."
It's not all about pretty pictures. Several science experiments were planned, including studies that could help in the search for habitable planets beyond Earth.
Telescopes, such as NASA's Kepler space telescope, are being used to find so-called extrasolar planets that pass in front of their parent stars, much like Venus passing by the sun.
During the transit of Venus, astronomers planned to measure the planet's thick atmosphere in the hope of developing techniques to measure atmospheres around other planets.
Studies of the atmosphere of Venus could also shed light on why Earth and Venus, which are almost exactly the same size and orbit approximately the same distance from the sun, are so different.
Venus has a chokingly dense atmosphere, 100 times thicker than Earth's, that is mostly carbon dioxide, a greenhouse gas.
Its surface temperature is a lead-melting 900 degrees Fahrenheit (480 degrees Celsius) and towering clouds of sulfuric acid jet around the planet at 220 miles per hour (355 kph) dousing it with acid rain.
"Venus is known as the goddess of love, but it's not the type of relationship you'd want," an astronomer said on the Slooh.com webcast. "This is a look-but-don't-touch kind of relationship."
Scientists are interested in learning more about Venus' climate in hopes of understanding changes in Earth's atmosphere.
During previous transits of Venus, scientists were able to
figure out the size of the solar system and the distance between
the sun and the planets.
Tuesday's transit is only the eighth since the invention of the telescope, and the last until Dec. 10-11, 2117. It also is the first to take place with a spacecraft at Venus.
Observations from Europe's Venus Express probe will be compared with those made by several ground and space-based telescopes, including NASA's Solar Dynamics Observatory, the joint U.S.-European Solar and Heliospheric Observatory and Japan's Hinode spacecraft.