The only planet left in the solar system with unseen territory (terra incognita) is Mercury — but not for very much longer. In January NASA's Messenger spacecraft encounters the closest rock to the Sun for the first of several flybys before finally entering orbit in 2011.
Because only about half of Mercury's surface was mapped in the mid-1970's by the Mariner 10 probe, amateurs still can contribute worthy science by targeting the planet during favorable elongations. Planetary enthusiast John Boudreau of Saugus, Massachusetts did just that earlier this month.Using his Celestron C-11 Schmidt-Cassegrain telescope at f/17 and an Imaging Source DMK 21AF04.AS video camera, Boudreau was able to record a detailed series of images in the mid-morning hours of November 4, 8, 11, 14, and 17, when the innermost planet had a particularly well-placed western elongation for Northern Hemisphere observers.
Boudreau explains that he used a near-infrared filter to darken the daytime sky and to increase the planet's contrast. On some mornings he waited until about 9:30 a.m. to allow the planet to rise high enough in the sky to photograph crisply.
A neighbor's much-cursed tree — normally a hindrance because it blocks Boudreau's eastern horizon — actually worked to his advantage this time by shading his backyard observatory and telescope. Direct sunlight creates localized heat currents that degrade the image at the telescope drastically.
Among other tricks, Boudreau used a bright red star (Arcturus was well placed at the time) to collimate his telescope before moving over to Mercury. The star had to be red, because blue stars are less visible in daylight.
He recorded very long series of video frames to assure that he'd have an adequate number of good ones to combine later using RegiStax. Each of his videos were 10,000 frames long, but the final stack for each image only utilized the 200 or so hand-selected best frames.
Boudreau notes that you don't need to live in a special location to record great pictures of the Sun, Moon, or planets — all it takes is patience and good technique. This Mercury movie and all the other images on his website are proof enough!
And to see how Boudreau's results compare with those from the big guns of professional astronomy, check out images of Mercury from the SOAR telescope released last month.