MARS IS Shrinking, Shrinking, Shrinking…
Jay Albert - April, 2010
The best views of Mars for the 2009-10 apparition are already behind us. As Mars shrinks below 8 arcseconds in diameter this month, any detail becomes increasingly difficult visually and fine detail is impossible. This has been the poorest apparition since I started seriously observing Mars and filing reports with the Association of Lunar & Planetary Observers (A.L.P.O.) in 2001. The reason for this poor showing is not only Mars’ diminutive size (a hair over 14 arcseconds at its largest), but the unusually cloudy and wet weather with numerous passing cold fronts we’ve experienced this winter “dry” season. This weather combination gave us overall poor conditions and even when it was clear, the seeing was generally bad enough to make Mars look like a featureless, vibrating orange ball. As a result, I had only about half my average number of Mars observations. I even had four nights when I had set up and aligned my C11only to find the seeing too poor to see anything more than Mars’ north polar cap and preventing me from making a drawing and filing an observation.
Tradition says that a planet needs to be at least 10 arcseconds in diameter in order to see and record detail visually. This limit, of course, is now much smaller with digital photography. I did manage to break this limit with my last two Mars observations, the tonal drawings of which are shown below. In line with the International Astronomical Union’s and ALPO’s convention, south is shown up and the east, or preceding limb, is to the left. Mars’ northern hemisphere is still tilted toward Earth, showing us more of the northern features than are normally visible during the apparitions when Mars comes closer to the Earth and is therefore larger in the eyepiece.In the below view, Mars’ best known feature, Syrtis Major, is seen near the preceding, or evening, limb. Below Syrtis Major, peaking over the southeast limb is the 1,300 miles wide and 4 to 5 miles deep Hellas Basin. The long arm extending west from Syrtis Major is Sabaeus Sinus, at the end of which is the Meridiani plain where the Opportunity Rover currently resides. In the north (bottom), the north polar cap can be seen with the dark Utopia region in the east and the Acidalia plain in the west.
I recorded the above view on the night of March31st -April 1st when the seeing was the best I’d had this apparition. This time, Syrtis Major is near the west or morning limb and separated from Cimmerium Mare by a thin bright area called Hesperia. The north polar cap is at bottom with Utopia pointing south (up) toward Syrtis Major.
I had hoped to get one last observation of the Solis Lacus region, popularly known as the “Eye of Mars”, last week but the weather didn’t cooperate. The next Mars apparition, about two years from now, will see Mars at its smallest size as seen from Earth. But the difference is size from this year’s apparition will be too small to notice, so Mars won’t be significantly more challenging than it was this time around. With better weather, we might even see more of the red planet.
April 17, 2010