The transit of Venus across the sun is one of the rarest celestial sights visible from Earth,
one that wowed scientists and amateur observers around the world Tuesday (June 5). The event, arguably the most anticipated skywatching display of the year, marked the last time Venus will cross the sun (as seen from Earth) for 105 years. Venus transits occur when Venus reaches a point in its orbit that brings the planet directly between the Earth and the sun. Since the tilt of Venus’ orbit isn’t exactly the same as that of Earth, the events are rare, occurring just four times every 243 years. The transits occur in pairs eight years apart. Since the June 5 transit followed a previous Venus sun crossing in 2004, this is the last one of the current cycle. Venus and Mercury are the only planets that can be seen crossing the sun from Earth since their orbits are between our planet and the sun. The next Mercury transit will be on May 9, 2016. Only seven Venus transits have been witnessed since the invention of the telescope 400 years ago, and you’d have a long wait for the next one. It won’t happen again until December 11, 2117. To celebrate the last transit of Venus in the 21st century, astronomers and skywatchers came together in many sites around the world. In the United States, NASA beamed images of the transit from an observatory atop Mauna Kea in Hawaii (just one of many webcasts from many countries) and welcomed the public to its various space centers, including the Ames Research Center in Moffett Field, Calif. Tuesday’s transit began just after 6 p.m. EDT (2200 GMT) and lasted about six hours and 40 minutes. It was visible across North America, Europe, Asia and eastern Africa. Because of the International Date Line, some parts of the world saw the transit on June 6. NASA and other space agencies trained a fleet of satellites to watch the Venus transit in unprecedented detail. NASA’s powerful Solar Dynamics Observatory captured spectacular photos and movies of the entire transit.