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Thursday, January 12, 2012

Heads up! Transit of Venus, 2012 June 5-6th

One of the rarest of celestial spectacles is the transit of the planet Venus in front of the disc of the Sun as viewed from the Earth. Indeed, this event did not occur at all in the twentieth century and takes place only twice in the twenty-first, the first of which, on June 8th, 2004, you've already missed. So it's either catch the big show on June 5–6th of 2012 or plan to hang in there until the next transit of Venus on the 11th of December 2117.

Fortunately, the 2012 transit of Venus occurs near the June solstice, when the Earth's northern hemisphere is tilted the most toward the Sun, and since the southern hemisphere is mostly water and ice, the vast majority of the human population will, given clear skies, be able to observe this celestial show. With the exception of people in western Africa, the west of Spain, Portugal, the eastern three quarters of South America, and Antarctica, the transit will be visible, although to many viewers the transit (which lasts about six hours) will already be in progress at sunrise or still be in progress at sunset. So while you may not be able to observe the whole thing, unless you happen to be in one of the sadly deprived regions this time, you'll at least be able to see Venus as “a spot, not a dot” crossing the disc of the Sun. The following map courtesy of Fred Espenak and NASA/GSFC shows visibility of the transit. As long as you're not in the darkest shaded area, you'll be able to see it if the weather cooperates.

You can observe the transit of Venus without any optical aid whatsoever apart from a safe solar filter to protect your eyes. For direct viewing with the unaided eye, eclipse specs will do the job. If you want to view or photograph the transit through binoculars, a telescope, or a camera lens, you'll need a full-aperture solar filter securely fastened in front of the objective. Polymer film filters are the most economical, but a glass, metal-coated filter will provide a sharper image and better contrast. Whatever filter you choose, be sure it is securely attached to your viewing device, as even instantaneous exposure to unfiltered sunlight through optics can result in blindness or destruction of camera equipment.

You may think this posting precocious, but if you're interested in observing, photographing, or recording the transit on video, now is the time to decide on the equipment and techniques you'll use, order any gear you don't have on hand, and practice observing and imaging the Sun with the equipment you'll use for the transit. And if, like mine, your full aperture solar filter is showing its age, take a close look at it and see how much its many adventures may have degraded its performance and consider retiring it in favour of one with fewer pinhole defects.

Transits—you want 'em all now?   Happy to oblige!

Posted at January 12, 2012 20:19