Utahns have a rare opportunity Monday to watch a sort of solar eclipse, one that can only be seen safely with the correct astronomical equipment.
In fact, the "eclipse" actually will be invisible without a telescope equipped with the proper sun filters. It is the passage of the planet Mercury between the sun and Earth, an event called the transit of Mercury.The last time one was visible from this region was in November 1960.
The diminutive planet is a mere fly speck compared with our nearest star. It is so tiny that it will not block sunlight to any appreciative amount, so the sun will be just as dangerous to vision as it is any other time.
But through the right kind of equipment, viewers should be able to spot the tiny, dark disk in front of the sun. Patrick Wiggins of Hansen Planetarium said the first contact of the disk will be on the sun's northern part at about 2:11 p.m., and the planet slowly glides across the solar disk for almost an hour.
It will finally leave the sun's face about 3:10 p.m.
"As rare and interesting as this event may be, observers must remember that as with any sun-observing activity, one must be very careful not to damage their eyes while watching it," Wiggins warned.
To help people observe the transit, Hansen Planetarium has posted information on its Starline Information Service, (801) 532-STAR.
In addition, the Salt Lake Astronomical Society and Midvale's Intermountain Optics will join forces with the planetarium for a special transit party in the parking lot of Harmon's food store, 7800 S. and 700 East in Midvale. The event continues from 1:30 until 3:30 p.m.
Several astronomical telescopes will be present equipped with special filters that are designed for safe solar viewing. The party is free, but will be held only if weather permits.
Also, Wiggins said, real-time images of the transit will be posted on the Internet via the Space News & Images link on the planetarium's web page http://www.utah.edu/planetarium.
The next time a transit of Mercury will be visible from the western United States will be in 2006. Transits of Venus also happen, but the next one visible in the West won't occur until 2125.