Astronomical Transits:

The dictionary offers this definition of a transit: pass across (a sign or house of the zodiac) or pass across (the disk of a celestial body or the meridian of a place); "The comet will transit on September 11"

On Wednesday, November 8, 2006, the planet Mercury will "transit" across the face of the Sun. If you happen to be at the right location on the planet earth you will be able to witness all or parts of the transit.

Mercury's path across the sun will be like this:

Things to watch for will be the various contacts. A contact is when the edge of one body touches the edge of another. In the cast of transits and eclipses, contacts can provide some interesting visuals.

Mercury Transit - November 8, 2006, Goleta, California

Second Contact - the sunspot on the left does have a number as of second contact time.

Second Contact - detail

Fuji S2 DSLR, Tamron 400mm w/ 2x extender, ISO400, Baader Photographic Solar Filter.

Contacts - Venus Transit, June 8,2004, Venice, Italy
lst Contact - first contact is when the transiting body touches the outside edge of the sun. This is difficult to see in a planetary transit due to the dark background created by the solar filter. In an eclips of the sun and moon, it's often a bit easier to see. Rely on the correct transit times to begin viewing the transit.


2nd Contact - once the transiting body is inside the orb of the sun it occurs just as the left edge of the planet leaves the first inside rim of the sun. In a planetary transit look for the "teardrop" effect where the departing edge leaves a neck or shadow, hence the name "teardrop" effect.

2nd Contact - Venus Transit, June 8, 2004, Venice Italy

Tear drop effect, Venus Transit, June 8, 2004, Venice, Italy

Comparing the planets. This is a composite of the Venus and Mercury transit at second contact. Note the size difference between the two planets.

In a total solar eclipse 2nd contact is responsible for Bailey's Beads, which is cause by light bending around the not-so-smooth edges of the moon. They are also known as Diamond Beads.


3rd Contact - At the closing end of the transit as the transiting body leaves the orb of the sun it's leading edge will touch the outside edge of the sun. This is third contact.

4th Contact - When the trailing edge of the planet touches the outside edge of the sun we have 4th contact.

Mid or Greatest Transit is when the transiting planet is midway across the face of the sun.<p>

Greatest Transit, Venus Transit, June 8, 2004, Venice, Italy

In a solar eclipe, greatest transit would be totality, when the moon is in the middle of the sun with light streaming out from all sides, such as this view from the June 21, 2001 total solar eclipse in Zimbabwe.

For this month's transit keep in mind Mercuyr is much smaller than Venus and also further away from the earth. It is 1/195 the diameter of the sun and will appear as a dot.

This is what Mercury look like in its 1999 transit from Santa Barbara, California.

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All images © 1998 - 2006 Anthony Galván III.
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