Mohawk Valley Astronomical Society

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Red Planet Reprise

by Perry Pezzolanella, MVAS

A dazzling orange star rising in the northeast by midnight in August heralds the chillier, longer evenings that lay ahead as Mars returns for an encore performance. It reaches opposition on November 7, which means it is up all night, but due to its highly elliptical orbit, it will be at its closest, largest, and brightest on October 30. On that date Mars will be 43.1 million miles from Earth and 20.2 arc-seconds across. It will shine at a radiating magnitude of -2.3. Although this is not as great as the 2003 opposition, Mars will still dominate the night sky for several months.

Mars is fascinating because it is the only planet that clearly reveals a solid surface. It is a desert world of rusted iron dust and sand grains formed by volcanoes and water, complete with towering volcanoes, deep canyons, and glittering white polar ice caps. The polar ice caps of water and carbon dioxide are the easiest to see and once again the south polar ice cap will be tipped towards Earth giving excellent views of the rapidly shrinking ice cap. The dominant dark and bright features that were prominent during 2003 will be in view again, provided there is no dust storm enveloping Mars. The darker, brown areas are primarily dust-free rock outcrops with the largest being a wedge called Syrtis Major. Meridiani Sinus (Meridiani Planum) is dark for a different reason. The Opportunity Rover landed here and found it to be a vast expanse of dark hematite grains that were once formed by an ancient shallow sea. Hellas is a deep impact basin over 1000 miles across that is filled with very fine, highly reflective dust that is so bright that it can be confused for ice clouds or the south polar ice cap. Several nights of observing with patience and steady seeing will gradually train the eye to focus on finer detail. Larger telescopes will improve the chances of seeing subtle detail along with the use of an orange or red filter. The features are usually subtle, but unlike the 2001 and 2003 oppositions, Mars will be higher above the horizon in Aries not far to the west of the Pleiades. This places it above the worst of the atmospheric turbulence. Mars will add an extra dazzling star to the dozens already present after Orion has full risen with its cohort of the Winter Hexagon.

The first row of diagrams that follow show a complete surface map of Mars with the most prominent features visible as well as the polar ice caps. Three different global views follow with the darkest and most prominent surface features shown. The dates in the third row indicate when these features will be nearly centered on Mars at 11PM EDT (10PM EST). These views are good for a few hours either way or a few days around the given dates. Since Mars rotates on its axis in 24 hours and 37 minutes, these features will shift throughout the night. The rotation rate from Syrtis Major to Meridiani Sinus is six hours. From Meridiani Sinus to Solis Lacus is another six hours. If Solis Lacus is visible, then it will be another twelve hours before Syrtis Major returns to view. The fourth row indicates the change in size and brightness for Mars during this apparition.

The best time to observe Mars is when it is larger than 10 arc-seconds across. This will occur from July 12 through January 18, which is an exceptionally long range due to its very close approach to Earth. Activities that were missed in 2003 can be accomplished this fall including photography, video imaging, plotting the shrinking polar ice cap and retrograde path of its position among the stars from September through January. See if Mars can cast a shadow on the newly fallen country snow and take note of the changing phases as Mars becomes noticeably gibbous by January with only 89% of its disk lit by the Sun from Earth's perspective.

Due to its very elliptical orbit, not all oppositions are as great as this one. The next opposition on December 24, 2007 will find Mars at only 15.9 arc-seconds across while those of 2010, 2012, and 2014 will display Mars smaller still. Mars will be better in 2016 and at the opposition of July 27, 2018 Mars will be even bigger than this year at 24.3 arc-seconds across, but who wants to wait thirteen years? Get out and see Mars! Witnessing this close return of the Red Planet on a chilly evening later this year will rekindle the spirit of the awesome opposition of 2003, and be an opportunity to add to the wealth of observations.