Tuesday, November 15, 2005

Playing with planets

Anyone who has been outside at night these past few weeks couldn't help but see Mars blazing away like a stoplight. High in the east as the Sun goes down, the red planet drifts across the sky all night, setting in the west just before sunrise. Last week Mars had an apparent magnitude of - 2.3, which rivals Jupiter at its brightest. It is fading now, but still bright enough to make someone who notices it for the first time exclaim, "Wow! What's that?"

Back in 1968-69, as a post-grad at London's Imperial College, I worked out the orbit of Mars that year using the theories of Claudius Ptolemy (2nd c. AD), Nicholas Copernicus, Tycho Brahe, and Johannes Kepler. I am not aware of anyone else who has done this, and I am sharing my diagrams from that time in my new book, Walking Zero: Discovering Cosmic Space and Time Along the Prime Meridian, to be published by Walker in the spring. Here is my unedited drawing for Ptolemy's theory, taking into account precession since his time. It matches closely the actual motion of Mars in the sky in 1968-69, and shows more vividly than later heliocentric theories the varying distance of Mars from the Earth, and hence brightness.