Starting Monday, we’re entering a three-week period when viewing the planet Mercury is the best it’s going to be for many moons.
Typically when viewed from Earth, Mercury is too close to the sun for easy viewing. Except for a brief opportunity to view the smallest planet in the solar system (we miss you, Pluto!) near sunset or sunrise, the sun’s glare is just too much and it blots out Mercury. Except, that is, from this Monday through March 12.
During this viewing window, Mercury is at enough of an elongation of its orbit around the sun that it should be more easily visible. In other words, as Mercury’s orbit around the sun stretches, its increased distance from the sun allows less light to interfere with viewing. “Easily viewable” is a relative term however, because at most mid- and northern latitude locations in North America and Europe, Mercury will be near the horizon and the light of twilight (or early dawn) will keep the planet lost or nearly-lost in the illuminated sky. Unfortunately for Northern Hemisphere viewers, Mercury is never above the horizon for nighttime viewing.
Little is known about Mercury because Earth-based telescopes reveal little (again, the light of the sun makes viewing difficult). In November, 1973 the satellite Mariner 10 traveled to Mercury with the mission of mapping the planet’s environment, atmosphere surface and other characteristics. Mariner 10 mapped about 45% of Mercury’s surface. In 2004, the MESSENGER satellite was launched into orbit around Mercury and mapped the remainder of the planet’s surface. MESSENGER’s mission has been extended to March of 2013.