Tuesday, July 14, 2009
Monday, July 13, 2009
MARS IN GALAXY
Mars has long exerted a pull on the human imagination.The erratically moving red star in the sky was seen as sinister or violent by the ancients: The Greeks identified it with Ares, the god of war; the Babylonians named it after Nergal, god of the underworld. To the ancient Chinese, it was Ying-huo, the fire planet. Even after Copernicus proposed, in 1543, that the sun and not the Earth was the center of the local cosmos, the eccentricity of Mars's celestial motions continued as a puzzle until, in 1609, Johannes Kepler analyzed all the planetary orbits as ellipses, with the sun at one focus.
In that same year Galileo first observed Mars through a telescope. By the mid-17th century, telescopes had improved enough to make visible the seasonally growing and shrinking polar ice caps on Mars, and features such as Syrtis Major, a dark patch thought to be a shallow sea. The Italian astronomer Giovanni Cassini was able to observe certain features accurately enough to calculate the planet's rotation. The Martian day, he concluded, was forty minutes longer than our twenty-four hours; he was only three minutes off. While Venus, a closer and larger planetary neighbor, presented an impenetrable cloud cover, Mars showed a surface enough like Earth's to invite speculation about its habitation by life-forms.
Increasingly refined telescopes, challenged by the blurring effect of our own planet's thick and dynamic atmosphere, made possible ever more detailed maps of Mars, specifying seas and even marshes where seasonal variations in presumed vegetation came and went with the fluctuating ice caps. One of the keenest eyed cartographers of the planet was Giovanni Schiaparelli, who employed the Italian word canali for perceived linear connections between presumed bodies of water. The word could have been translated as "channels," but "canals" caught the imagination of the public and in particular that of Percival Lowell, a rich Boston Brahmin who in 1893 took up the cause of the canals as artifacts of a Martian civilization. As an astronomer, Lowell was an amateur and an enthusiast but not a crank. He built his own observatory on a mesa near Flagstaff, Arizona, more than 7,000 feet high and, in his own words, "far from the smoke of men"; his drawings of Mars were regarded as superior to Schiaparelli's even by astronomers hostile to the Bostonian's theories. Lowell proposed that Mars was a dying planet whose highly intelligent inhabitants were combating the increasing desiccation of their globe with a system of irrigation canals that distributed and conserved the dwindling water stored in the polar caps.
In that same year Galileo first observed Mars through a telescope. By the mid-17th century, telescopes had improved enough to make visible the seasonally growing and shrinking polar ice caps on Mars, and features such as Syrtis Major, a dark patch thought to be a shallow sea. The Italian astronomer Giovanni Cassini was able to observe certain features accurately enough to calculate the planet's rotation. The Martian day, he concluded, was forty minutes longer than our twenty-four hours; he was only three minutes off. While Venus, a closer and larger planetary neighbor, presented an impenetrable cloud cover, Mars showed a surface enough like Earth's to invite speculation about its habitation by life-forms.
Increasingly refined telescopes, challenged by the blurring effect of our own planet's thick and dynamic atmosphere, made possible ever more detailed maps of Mars, specifying seas and even marshes where seasonal variations in presumed vegetation came and went with the fluctuating ice caps. One of the keenest eyed cartographers of the planet was Giovanni Schiaparelli, who employed the Italian word canali for perceived linear connections between presumed bodies of water. The word could have been translated as "channels," but "canals" caught the imagination of the public and in particular that of Percival Lowell, a rich Boston Brahmin who in 1893 took up the cause of the canals as artifacts of a Martian civilization. As an astronomer, Lowell was an amateur and an enthusiast but not a crank. He built his own observatory on a mesa near Flagstaff, Arizona, more than 7,000 feet high and, in his own words, "far from the smoke of men"; his drawings of Mars were regarded as superior to Schiaparelli's even by astronomers hostile to the Bostonian's theories. Lowell proposed that Mars was a dying planet whose highly intelligent inhabitants were combating the increasing desiccation of their globe with a system of irrigation canals that distributed and conserved the dwindling water stored in the polar caps.
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