Celestial Gallery

Transit of Mercury

On 8 November 2004, the planet Mercury made one of its journeys across the face of the sun, as seen from Earth.  While following their own separate orbits around the sun, it just so happened that on this date, Mecury and the Earth were in a direct line with the sun.  As Mercury is somewhat closer to the sun, observers on Earth saw the planet move slowly across the sun's disk.

The entire event started at about 11:12am (Pacific Time) and lasted about 5 hours.  (South is at top, for all images on this page.)

In the image at left, which was taken about an hour into the transit, Mercury can be seen as a small round dot at approximately the "one-o'clock" position.  (A sunspot also appears at the edge of the disk.)

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In the image below, taken about an hour later, Mercury has moved noticeably.  A closeup of the planet, which appears decidedly round in shape, can be seen below right.

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The full disk of the sun can be seen below, with Mercury now having moved across the center line of the disk.  More sunspots can be seen at the left edge of the sun.

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In the last image, at right, Mercury has moved farther, and is about 90 minutes from "egress"--the end of the transit, at which the planet finally moves off the disk.

A transit event is much like a solar eclipse.  In an eclipse, the moon moves in front of the sun.  Although much smaller in size than the sun, the Moon is a great deal closer to us, so appears to be approximately the same size as the sun in the sky; thus, it can block the view of the solar disk.

This is generally the same general phenomenon that happens during a transit.  The difference is that the object that crosses the sun appears to be much smaller than the sun itself, due to its size and much greater distance from the earth.

A transit of Mercury across the sun happens about 13 times per century, and occurs only when Mercury, the Earth, and the sun are in a direct line.