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November 8, 2006: Mercury transits across the Sun

Mercury, the innermost planet of the solar system, passes in between the Earth and Sun three to four times a year, an event that astronomers call an inferior conjunction. More often than not, however, Mercury in its orbit passes above or below the Sun, and Mercury's inferior conjunction comes to pass without any notice or fanfare.

Once in a great while -- some 13 to 14 times a century -- Mercury at inferior conjunction passes directly between the Earth and Sun. As seen from Earth, Mercury then appears as a small black dot silhouette in front of the solar backdrop, and this is what's called a transit of Mercury. Keep in mind that proper eye protection is absolutely essential for watching this or any transit, else you risk severe eye injury, or blindness.

Fortunately, you don't have to know much about telescopes or solar filters to observe this transit safely, since numerous observatories, planetariums and astronomy clubs will be giving public viewings of the Mercury transit. (For another observatory listing, try this link.) If you're close to Potsdam, NY, the Clarkson University Reynolds Observatory will be hosting a transit watch (weather permitting), with the gates opening at 1:30 p.m. on November 8.

Transit Information

The 5-hour transit starts on November 8, around 19:12 (7:12 p.m.) Universal Time and ends on November 9, around 0:10 (12:10 a.m.) UT. What this means is that for North and South America, the transit takes place in the afternoon hours on November 8, while in Asia, Australia and New Zealand, Mercury transits the Sun during the morning hours on November 9.

For our Eastern Time zone in Potsdam, NY, the transit happens on the 8th, from about 14:12 (2:12 p.m.) till 19:10 (7:10 p.m.). But since the Sun sets at 16:40 (4:40 p.m.), the curtains close halfway through the production, right at the climax. Mercury comes closest to the center of the Sun around 16:41 (4:41 p.m.) Eastern Standard Time. The West Coast, on the other hand, gets to see the transit from start to finish. For the rise/set times of the Sun and Mercury in your sky, check Old Farmers Almanac or the US Naval Observatory.

The following links provide a map and a lot more information on the Mercury transit, courtesy of Fred Espenak, a master on the subject of eclipses. Exploratorium will feature a live webcast of the event.

For geometrical aspects of Mercury transits, read Mercury Transit Cycles.

copyright 2006 by Bruce McClure

October 2006 Feature * December 2006 Feature

Mercury Transit Cycles

Reynolds Observatory