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 (2001-2007), 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 December 05, 2008 (168.5° Ls); however, Mars will disappear behind the Sun around November 21, 2008 and will not emerge from the Sun until 28 days later on December 18.

The apparent declination of Mars begins at 18.8° in mid-January 2010 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 August 1, 2010.  By October 29, 2009, a 0.5 visual magnitude Mars is seen rising early in the morning sky in the constellation Cancer, it will be at western quadrature (90° west of the Sun) and the phase or terminator will be at its widest (40°).

In 2010 Mars begins retrogression, or retrograde motion against the background stars just over a year after from December 22, 2009 (18° Ls) through March 11, 2010 (62° Ls). Each night for this brief period before, during and after opposition the Red Planet will appear to move backwards toward the western sky sky from the constellation Leo into Cancer.

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 2010 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 2010 Mars apparition is considered transitional because the orbital longitude at opposition will be only 26° from the aphelion longitude 70° Ls (Ls will be defined later).

Closest approach occurs at 1844 UT on January 27, 2010 (43.8° Ls) with an apparent planetary disk diameter of 14.11'' at a distance of 0.663989469429 astronomical units (AU) or 61,721, 554 miles (99,331,411 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.

Opposition occurs nearly fourteen 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 about five weeks after that retrogression begins. Opposition will occur at 1948 UT on January 29, 2010 (44.3° Ls), with an apparent planetary disk diameter of 14.1 arcsec. Mars will remain visible for nearly a year after opposition and then become lost in the glare of the Sun again (January 21, 2011) as it approaches the next conjunction (February 6, 2011). The cycle is complete in 780 Earth days.
 
 

Figure 2. A simulated view of the appearance of Mars during opposition at 1948 UT on January 29, 2010 (44.3° Ls).

The observable disk diameter of Mars will be greater than 6 arcsec from September 8, 2009 [23.5° d ] (334.8 ° Ls) and will not fall below this value until June 01, 2010 [13.9 ° d ] (98.4° Ls), lasting nearly 9 months or 124 degrees Ls. During a similar profile in 2007 Mars began at 6 arcsec on June 14, 2007 [7.2° d] (257.1° Ls) and continued to April 24, 2008 (62.8° Ls), equaling equaling 10 and a half months or 166 degrees Ls.  Imaging by CCD devices may begin with a disk diameter of 4 arcsec or less, commencing on February 04, 2009.

During closest approach in 2010 the apparent diameter of Mars will be more nearly 2 arcsec smaller than it was at the same period in 2007 and it will be nearly 5 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 2009 and 2010 Ephemeris of Mars is tabulated the following URL: http://www.tnni.net/~dustymars/eph09_10.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 September 08, 2009 to a maximum diameter on January 28, 2010, and then shrink as it moves away.  Closest approach occurs on January 17, 2007 (Opposition January 29, 2010).  From September 2009 through June 2010 are the prime observing months.

Figure 4. Graphic Ephemeris of Mars during the 2009-2010 apparition from October 27, 2009 through July 19, 2010.   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 October 27, 2009 through July 19, 2010.  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 2009 and throughout 2010.  On August 15, 2009 the Martian North Polar Region (NPR) will begin to tilt towards the Earth and will remain so for the remainder of the apparition.  However, the opposite side of the northern part of polar cap will in the terminator shadow until October 27, 2009 when the cap will be sunlit, except where covered by the eastern terminator that will be present.

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 -24.2°, will be on or about May 03, 2009; however, Mars will only be 4.5 arcsec in apparent diameter then.  A better time to see possible flashes would be either on or about January 20, 2010 when the De and Ds will be at 15.8° and again on or about June 17, 2010 when the De and Ds are coincident at 23.8°.

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

For those interested in catching a glimpse of possible "flashes" from the surface of Mars there will be two periods when possible "flashes" may be seen on Mars. The first occasion when the De and Ds are coincident will be on or about January 20, 2010 and again be on or about June 17, 2010. See tables below for dates when De = Ds +/- 1.0 degree:

First Period: EST = UT - 5 || Di = 13.84" through 14.08"
 

Second Period: EDT = UT - 4 || Di = 5.77" through 5.40"
 

NOTE: Di = apparent diameter of Mars
            De = Declination of Earth from Mars
            Ds = Declination of Sun from Mars
            De - Ds = coincident
            i = phase defect in degrees