Transit of Venus

Diagram showing how transits of Venus occur an...

Diagram showing how transits of Venus occur and why they don’t occur frequently. Drawn by User:Theresa Knott; License see: (Photo credit: Wikipedia)

2012 transit of Venus, when the planet Venus appeared as a small, dark disk moving across the face of the Sun, began at 22:09 UTC on 5 June 2012, and finished at 04:49 UTC on 6 June. Depending on the position of the observer, the exact times varied by up to ±7 minutes. Transits of Venus are among the rarest of predictable celestial phenomena and occur in pairs, eight years apart, which are themselves separated by more than a century: The previous transit of Venus took place on June 8, 2004 (preceded by the pair of appearances on December 9, 1874 and December 6, 1882), and the next pair of transits will occur December 10-11, 2117, and in December 2125.

Observations of the event

Visibility map

The entire transit was visible from the western Pacific Ocean, northwesternmost North America, northeastern Asia, Japan, the Philippines, eastern Australia, New Zealand, and high Arctic locations including northernmostScandinavia, and Greenland. In North America, the Caribbean, and northwestern South America, the beginning of the transit was visible on 5 June until sunset. From sunrise on 6 June, the end of the transit was visible from South Asia, the Middle East, east Africa, and most of Europe. The phenomenon was not visible from most of South America, nor from western Africa. There were a number of live online video streams with footage from telescopes around the world. Midway through the transit one of the NASA streams had nearly 2 million total views and was getting roughly 90,000 viewers at any given moment.

In Los Angeles, crowds jammed Mount Hollywood where the Griffith Observatory set up telescopes for the public to view the transit. In Hawaii, hundreds of tourists watched the event on Waikiki Beach where theUniversity of Hawaii set up eight telescopes and two large screens showing webcasts of the transit. The transit was also observed and photographed by a flight engineer aboard the International Space Station, Don Pettit.

High definition images of the event were provided by NASA’s Solar Dynamics Observatory, from 36,000 km (22,000 mi) above the Earth. Agency astrophysicist Dr. Lika Guhathakurta said, “We get to see Venus in exquisite detail because of SDO’s spatial resolution, SDO is a very special observatory. It takes images that are about 10 times better than a high-definition TV and those images are acquired at a temporal cadence of one every 10 seconds. This is something we’ve never had before”. (SOHO was not in a good position to view the transit due to the size of its lissajous orbit centered about L1.)


The 2012 transit gave scientists a number of research opportunities. These included:

  • Measurement of dips in a star’s brightness caused by a known planet transiting a known star (the Sun). This will help astronomers when searching for exoplanets. Unlike the 2004 Venus transit, the 2012 transit occurred during an active phase of the 11-year activity cycle of the Sun, and would have provided practice in detecting a planet’s signal around a “spotty” variable star.
  • Measurement of the apparent diameter of Venus during the transit, and comparison with its known diameter. This will have given information on how to estimate exoplanet sizes.
  • The number of locations documenting the event will provide much data via parallax that will generate more accurate measurements.
  • Observation of the atmosphere of Venus simultaneously from Earth-based telescopes and from the Venus Express spacecraft. This gave a better opportunity to understand the intermediate level of Venus’s atmosphere than is possible from either viewpoint alone, and should provide new information about the climate of the planet.
  • Spectrographic study of the atmosphere of Venus. The results of analysis of the well-understood atmosphere of Venus will be compared with studies of exoplanets with atmospheres that are unknown.
  • The Hubble Space Telescope used the Moon as a mirror to study the light reflected from Venus to determine the makeup of its atmosphere. This may provide another technique to study exoplanets.

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