terça-feira, 5 de junho de 2012

VENUS TRANSIT 2012

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THE LAST TRANSIT ...IN OUR LIFETIME


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The next transit of Venus, when the planet Venus will appear as a small, dark disk moving across the face of the Sun, will begin at 22:09UTC on 5 June 2012, and will finish at 04:49 UTC on 6 June.[1] Depending on the position of the observer, the exact times can vary by up to ±7 minutes. Transits of Venus are among the rarest of predictable celestial phenomena and occur in pairs eight years apart:[2] theprevious transit having been in June 2004, the next pair of transits will not occur until December 2117 and December 2125.


Visibility

The entire transit will be visible from the western Pacific Ocean, northwesternmost North America, northeastern Asia, Japan, thePhilippines, eastern Australia, New Zealand, and high Arctic locations including northernmost Scandinavia, and Greenland.[3] In North America, the Caribbean, and northwestern South America, the beginning of the transit will be visible on 5 or 6 June until sunset. From sunrise on 6 June, the end of the transit will be visible from South Asia, the Middle East, east Africa and most of Europe. It will not be visible from most of South America or western Africa.

Research

The 2012 transit will give scientists a number of research opportunities. These include:[4][5][6]
  • 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 occurs during an active phase of the 11-year activity cycle of the Sun, and is likely to provide 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 give information on how to estimate exoplanet sizes.
  • Observation of the atmosphere of Venus simultaneously from Earth-based telescopes and from the Venus Express spacecraft. This will give a better opportunity to understand the intermediate level of Venus's atmosphere than is possible from either viewpoint alone, and will 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 will use 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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Observing

The safest way to watch a transit is to observe an image of the Sun projected onto a screen through a telescope, binoculars, pinhole[7] or reflected pinhole.[8] The event can be viewed without magnification using filters specifically designed for this purpose, such as an astronomical solar filter or eclipse viewing glasses coated with a vacuum-deposited layer of chromium. However, the disk of Venus is tiny compared to the sun and not much will be seen. The once-recommended method of using exposed black-and-white film as a filter is not considered safe now, as small imperfections or gaps in the film may permit harmful UV rays to pass through. Observing the Sun directly without appropriate protection can damage or destroy retinal cells, causing temporary or permanent blindness.[9][10][11]
NASA is airing a live webcast of the transit from Mauna Kea, Hawaii.[12

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