Always an intriguing world, Mars offers both casual and serious observers many challenges and delights. It also provides astronomers a laboratory to study the atmosphere and surface of another planet, including the behavior of condensates and their effects on its atmosphere and surface. Mars is similar to Earth in that it has four seasons, exhibits global climates, changing weather patterns, annual thawing and growing of polar caps, storm clouds of water ice, howling dusty winds, and a variety of surface features that predictably change in color and size and appear to shift position over extended periods of time.

Mars appears more Earth-like to us than most of the other planets because we can observe its surface, atmospheric clouds and hazes, and its brilliant white polar caps.  The latter are composed of frozen CO2 and underlying water ice, and wax and wane during the Martian year. These aspects, along with the changing seasons and the possibility of life, have made Mars one of the most studied planets in our solar system.

The Red Planet Mars offers both casual and serious observers many challenges and delights, as well as providing astronomers a laboratory to study another planet's atmosphere and surface. Some Martian features even appear to shift position around the surface over extended periods of time.

There are several cooperating international Mars observing programs under way to assist both professional and amateur astronomers. These include the International Mars Patrol (I.M.P.) coordinated by the Mars Section of the Association of Lunar and Planetary Observers (A.L.P.O), the International MarsWatch, the Terrestrial Planets Section of the British Astronomical Association (B.A.A.), and the Mars Section of the Oriental Astronomical Association (O.A.A.).

Information for observing Mars during a typical apparition is presented in a separate report titled, “General Information for Apparitions of Mars.” This report can be found on the Internet at URL: http://www.tnni.net/~dustymars/General_Info_Mars.htm

With the advent of modern CCD camera technology the amateur can produce useful images of Mars when it is as small as 3.5 arcsec. Early in an apparition, Mars rises in the east or morning sky and sets with the rotation of the Earth in the western or evening sky.  During the past few apparitions (2001-2010), observers began to take CCD images when Mars was only 32 degrees away from the Sun.  Since Mars was only a visual magnitude of ~1.8 then the planet would have been difficult to locate bright twilight hours.

In the pre-apparition reports the observer will find the motion of Mars in our sky, the characteristics for that particular apparition, information pertaining to the polar cap(s) and any special events that may be seen during that particular apparition.  As usual a calendar of events will be included with each report that contains cardinal dates for seasonal activity and orbital information of Mars.

As a general rule, an "apparition" begins when a planet emerges from the glare of the Sun shortly after conjunction. Mars will be in conjunction when the Sun on February 04, 2011 (229.9° Ls); however, Mars will disappear behind the Sun around January 20, 2011 and will not emerge from the Sun until 36 days later on February 25, 2011.

The apparent declination of Mars begins at 6.0° in mid-January 2012 and continues to climb northward until opposition. This is good news for those observing in the Northern Hemispheres because Mars will be seen high in their sky. Mars will be above the celestial equator until July 06, 2012. By December 02, 2011, a 0.7 visual magnitude Mars is seen rising early in the morning sky in the constellation Leo, it will be at western quadrature (90° west of the Sun) and the phase or terminator will be at its widest (37°).

In 2012 Mars begins retrogression, or retrograde motion against the background stars stars just over a year after from January 25, 2012 (61.5° Ls) through April 16, 2012 (97.5° Ls). Each night for this brief period before, during and after opposition the Red Planet will appear to move backwards toward the western sky from the constellation Virgo into Leo.

Since the Martian year is about 687 Earth days long -- nearly twice as long as ours, the Martian seasons are similarly extended. While the Earth's seasons are nearly equal in duration, the Martian seasons can vary by as much as 52 days from each other due to that planet's greater orbital eccentricity (see Figure 1)

Figure 1. A heliographic chart of the orbits of Mars and the Earth showing the relative seasons of both planets in the planetocentric longitude system Ls. Graphic Ephemeris for the 2012 Aphelic Apparition of Mars. Original graph prepared by C.F. Capen and modified by J.D. Beish.

Another general rule for predicting oppositions of Mars is from the following: the planet has an approximate 15.8-year periodic opposition cycle, which consists of three or four Aphelic oppositions and three consecutive Perihelic oppositions. Perihelic oppositions are also called "favorable" because the Earth and Mars come closest to each other on those occasions. We sometimes refer to this as the seven Martian synodic periods. This cycle is repeated every 79 years (± 4 to 5 days) and, if one were to live long enough, one would see this cycle nearly replicated in approximately 284 years. The 2012 Mars apparition is considered Aphelic because the orbital longitude at opposition will be only 8° from the aphelion longitude 70° Ls (Ls will be defined later).

Opposition occurs thirteen months after conjunction, when Mars is on the opposite side of the Earth from the Sun. At that time, the two planets will lie nearly in a straight line with respect to the Sun, or five weeks after that retrogression begins. Opposition will occur at 2013 UT on March 03, 2012 (78.1° Ls), with an apparent planetary disk diameter of 13.9 arcsec. Mars will remain visible for a year after opposition and then become lost in the glare of the Sun again (April 01, 2013) as it approaches the next conjunction (April 17, 2013). The cycle is complete in 780 Earth days.

Closest approach occurs at 0918 UT on March 05, 2012 (79.0° Ls) with an apparent planetary disk diameter of 13.9'' at a distance of 0.6736523625 astronomical units (AU) or 62,619,774 miles (100,776,960 km). [NOTE: one (1) A.U. equals 92,955,621 miles or 149,597,870 km]. It should also be noted that closest approach between Earth and Mars is not necessarily coincident with the time of opposition but varies by as much as two weeks.

Figure 2. A simulated view of the appearance of Mars during opposition at 1947 UT on March 03, 2012 (78.1° Ls)

The observable disk diameter of Mars will be greater than 6 arcsec from seconds November 04, 2011 [14.3° d ] (24.7° Ls) and will not fall below this value until July 21, 2012 [-3.7° d ] (142.5° Ls), lasting more than 8 months or 118 degrees Ls. During a similar profile in 2010 Mars began at 6 arcsec on September 8, 2009 [23.5° d ] (334.8 ° Ls) and did not fall below this value until June 01, 2010 [13.9° d ] (98.4° Ls), equaling nearly 9 months or 124 degrees Ls. Imaging by CCD devices may begin with a disk diameter of 4 arcsec or less, commencing on April 13, 2011.

During closest approach in 2012 the apparent diameter of Mars will be 0.21 arcsec smaller than it was at the same period in 2010 and it will be 12 degrees lower in the sky – not great for observing the Red Planet.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 3 and 4. The 2011 and 2012 Ephemeris of Mars is tabulated the following URL: http://www.tnni.net/~dustymars/eph11_12.html A glossary of Terms appears at the end of this table.

Figure 3. As it approaches Earth, it will swell from a small apparent disk of 6" in November 04, 2012 to a maximum diameter on March 03, 2012, and then shrink as it moves away.  Closest approach occurs on March 05, 2012 (Opposition March 03, 2012).  From November 2012 through July 2012 are the prime observing months.

Figure 4. Graphic Ephemeris of Mars during the 2011-2012 apparition from September 14, 2011 through September 30, 2012.   Opposition and 6 arcsec apparent diameter range arc indicated. Plot illustrates the Declination (blue line),   the latitude of the Sub-Earth point (De) or the apparent tilt (green line) in areocentric degrees, and the latitude of the Sub-Solar point (red line) in areocentric degrees.  The areocentric longitude (Ls) of the Sun, shown along the bottom edge of the graph defines the Martian seasonal date.  The value of Ls is 0° at the vernal equinox of the northern hemisphere, 70° when Mars is at aphelion, and 90° at the summer solstice of the northern hemisphere 250° when Mars is at perihelion, and 180° is northern autumn.

Figure 5. Graphic Ephemeris of Mars from September 14, 2011 through September 30, 2012.  Plot illustrates the apparent diameter of Mars in seconds of arc.  The areocentric longitude (Ls) of the Sun, shown along the bottom  edge of the graph defines the Martian seasonal date.

Astronomers will have an excellent view of the prominent north polar cap during most of the next apparition because it will be tilted earthward during the last half of 2011 and through mid-November 2012. On July 26, 2011 the Martian North Polar Region (NPR) will begin to tilt towards the Earth and will remain so for the remainder of the apparition.

For those interested in catching a glimpse of possible "flashes" from the surface of Mars the first occasion when the De and Ds are coincident at 23.4° , will be on or about February 03, 2012 when Mars will be 12 arcsec in apparent diameter. The next period for possible flashes will be on or about May 09, 2012 when the De and Ds are coincident at 23.5° .

For more detailed information on the north polar cap click to the URL: http://www.tnni.net/~dustymars/NPR.htm