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Mercury
Photograph courtesy NASA
Craters and scarps mark the surface of Mercury, the smallest planet in the solar system (after Pluto's downgrade to a dwarf planet) and the closest to the sun. Mercury's elliptical orbit takes the planet as close as 29 million miles (47 million kilometers) to the stormy star. Mercury speeds around the sun every 88 days, traveling through space at nearly 31 miles per second (50 kilometers per second) faster than any other planet. The length of one Mercury day is equal to 58.646 Earth days.
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Plane of the Ecliptic
Photograph courtesy NASA
The plane of the ecliptic is illustrated in this Clementine star tracker camera image that reveals, from right to left, the moon, the sun's corona rising over the moon's dark limb, and the planets Saturn, Mars, and Mercury. The ecliptic plane is defined as the imaginary plane containing the Earth's orbit around the sun. In the course of a year, the sun's apparent path through the sky lies in this plane. The planetary bodies of our solar system all tend to lie near this plane, since they were formed from the sun's spinning, flattened, proto-planetary disk.
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Mercury Transit
Photograph courtesy NASA Goddard Space Flight Center
Seen only as a black dot, Mercury makes a rare pass in front of the sun on May 7, 2003. These transits occur just 13 times each century. Because Mercury is so close to the sun, it is hard to directly observe from Earth except during twilight—and during these transits.
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