Mercury Crosses the Sun

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November 15, 1999

Poor little Mercury. Such a tiny planet, trapped so close to the sun! Not only blasted by the sun's rays, but usually difficult to see from earth due to glare of those rays. On a rare occasion such as this, called a transit, Mercury passes directly in front of the sun's disk, and you would think that would make it even harder to see. But with a telescope with sufficient magnification, fitted with a proper solar filter to safely dim the sun's blinding brilliance, a transit is actually the best time to see Mercury.

Although it is not even 1/200th the diameter of the sun, the silhouette of Mercury leaps into view, so dark and hard-edged that it seems a hole has been punched through the sun's disk.

A grazing transit such as this one, when Mercury crosses just within the Sun's edge, is the rarest of all. In fact, this was the first grazing transit of Mercury visible from earth since the invention of the telescope 400 years ago!

Many sunspots can also be seen on the face of the sun, since we were approaching the maximum of the 11-year solar cycle.

This photograph appeared on NASA's Astronomy Picture of the Day site on December 10, 1999.

Date: November 15, 1999
Time: Approximately 2:43pm MST
Location: Phoenix, Arizona
Equipment: Olympus OM-1 35mm camera at Cassegrain focus of 8" Celestron telescope with solar filter
Focal length: 2032mm
Aperture ratio: f/10
Film: Fujichrome 50 slide
Exposure time: 1/30 second
Scanner: Nikon Coolscan LS-10E
Photographers: Joe Orman and Rick Scott.

Revised: February 14, 2012
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