On the afternoon of Wednesday, Nov. 8, the tiny planet Mercury will pass in front of the sun creating what astronomers call a "transit of Mercury." According to NASA Solar System Ambassador Patrick Wiggins, "On average there are only about 13 Mercury transits per century. The last one visible from Utah occurred in 1999 and we won't see another until 2016."
Those with a properly filtered telescope should be able to see Mercury's tiny, dark disk first touch the lower left portion of the sun at about 12:12 p.m. MST. The planet will then glide slowly across the solar disk for about 5 hours.
Sunset will cause Utahns to miss the last few minutes of the transit but observers farther west will see Mercury leave the Sun's face at about 5:09 p.m.
"As rare and interesting as this event will be, observers need to be very careful not to damage their eyes while watching it," Wiggins cautions.
To help people safely observe the transit the Salt Lake Astronomical Society will host a free Mercury transit watch. The watch will be in the parking lot of the Harmon's grocery store located at 7800 S. 700 East in Midvale between noon and 5 p.m.
The transit watch will feature several telescopes equipped with special filters designed for safe solar viewing, including some which will allow viewers to see massive eruptions arcing away from the sun as tiny Mercury slowly treks across it.
Admission to the transit watch is free, however it will be hosted only if the weather permits.
Near real time images of the event will also be available via links on Wiggins' web page, http://utahastro.info/.
Venus is the only other planet to pass in front of the sun, but its transits are much rarer, averaging less that two per century. The next one will occur in 2012. After that earthbound observers will not see another transit of Venus until 2117.