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Red Planet Rally

by Perry Pezzolanella

A brilliant tiger-hued star will usher in the welcoming warmth of spring and lure the curious into the night to carefully scrutinize its changes as the year unfolds. The tiger-hued star is Mars, and it will return to the evening sky for another opposition on April 8, which means it will be up all night; however, due to its highly elliptical orbit, it will be at its closest, largest, and brightest on April 14. On that date Mars will be 57.4 million miles from Earth and 15.2 arcseconds across, sparkling at magnitude -1.5.

Mars is interesting to observe because it is the only planet that clearly displays a solid surface. It is a rusty desert world of windswept sand dunes, towering volcanoes, gaping canyons, craters, and two polar ice caps. These polar ice caps are the easiest to see and are composed of frozen water and carbon dioxide. During this opposition, the north polar ice cap, which will point towards Earth, will be prominent like it was during the 2012 opposition, but it should be free of haze and clouds as springtime in that hemisphere will be well under way. It will be fascinating to watch the changes as the ice cap slowly sublimates and recedes as summer approaches. Mars has several dark and bright features that will be visible provided there are no dust storms raging across the planet at the time. The darker, brownish areas are primarily dust-free rock outcrops with the largest and darkest being a wedge called Syrtis Major. Sinus Meridiani (Meridiani Planum) is where the Opportunity Rover landed a decade ago in January 2004 and continues to explore. Solis Lacus is another prominent dark feature that looks like an eye and is often nicknamed the "Eye of Mars". Hellas is a deep impact basin over 1000 miles across that is filled with very fine, highly reflective dust that can be confused for clouds or the south polar ice cap. Mars demands extreme patience when it comes to observing; several nights of observing will train the eye to focus on detail. Larger telescopes will improve the view along with the use of orange or red filters. The features are usually subtle and Mars will be lower during this apparition in Virgo, close to Spica, and could be bothered by air turbulence and the eventual haze of summer.

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 10PM EST (11PM EDT). These provide views 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 Sinus Meridiani is six hours. From Sinus Meridiani 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 arcseconds across. This will occur from February 14 through June 23, which will provide ample time to train the eye enough to make sketches or to take photos and video. The retrograde path of Mars among the stars from March 1 until May 20 can also be observed and plotted. Take note of the changing phases of Mars as it becomes noticeably gibbous by July with only 87% of its disc being lit by the Sun as seen from Earth.

Due to its very elliptical orbit, not all oppositions of Mars are good, but this one will be better than the past two. Mars will then rally for the three great oppositions that lie ahead. During the opposition of May 22, 2016 Mars will be 18.2 arcseconds across and the opposition on July 27, 2018 is the best until 2035 at 24.3 arcseconds across. The opposition of October 13, 2020 will also be an impressive 22.6 arcseconds across. Mars is now the primary focus of planetary exploration so why not make an effort and take the time to see what Mars can reveal tonight?