It's your last chance to watch transit of Venus

AGENCIES

PARIS: Witnessed only seven times since the time of Galileo, Venus’s solar crossing on Wednesday (in North America, the transit will start in the hours before sunset on Tuesday) is a rare and historic event that should not be missed.

Unless modern science discovers a way to delay or halt the aging process, this will be the last Venus transit we’ll ever get to see in our lifetime — the next transit won’t take place until 2117, or 105 years from now.

The transit of Venus in 2012 will begin at about 15:09 PT (23:09pm GMT Tuesday) and last nearly seven hours as Venus crosses the face of the sun.

Observers on seven continents, including part of Antarctica, will be able to see the Venus transit. For skywatchers in Asia, Australia Africa and Europe the event will occur on Wednesday due to the International Date Line.

How can Venus transit photographers capture the rare celestial sight safely?

The basic requirements for photographing the transit with a digital camera are very much the same as those for imaging sunspots or a partial solar eclipse.

From Earth, Venus will appear to cover just 1/32 of the face of the sun, so you’ll need ‘very good conditions and very good eyes’ to view the event without magnification, according to Nick Schneider, an astronomer at the University of Colorado, Boulder. But you still need protective eyewear, because without it, the intensity of the sun’s light can cause serious retina damage.

Why so rare?

• Transits of Venus occur in pairs eight years apart separated by either 105.5 years or 121.5 years

• Last one occurred in 2004; next pair won’t happen until 2117 and 2125

• There have been only seven transits of Venus since the invention of the telescope in 1610

How to photograph

• Filter! Filter! Filter!: Protect your eyes and equipment by using a proper, visually safe solar filter to cut down the sun’s intense brightness and heat

• Use a telescope or telephoto lens: To produce a reasonably large image of the sun with a digital camera, you’ll need a telephoto lens or telescope with a focal length of 500 to 1,000 millimeters, or even longer * Shoot at high resolution: Shoot images using high-resolution formats such as the highest-quality JPEG or uncompressed TIFF or RAW files

• ‘Bracket’ your exposures: You can either use the camera’s auto-exposure mode or manual mode to determine your exposure settings. If you prefer to do it manually, try various combinations of shutter speed, f-stop, and ISO speed — a technique known as ‘bracketing’ — and see which ones would come out best and use that as a guide. Don’t be afraid to experiment

• Check the latest weather forecast: Get the latest weather update from websites such as the National Weather Service, AccuWeather, The Weather Channel or Weather Underground