THE 2011-2012 APHELIC APPARITION OF MARS
By: Jeffrey D. Beish (12-08-2011)

ABSTRACT

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.
INTRODUCTION

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 and the Terrestrial Planets Section of the British Astronomical Association (B.A.A.).  

Information for observing Mars during a typical apparition is presented in a separate report titled, “General Information for Apparitions of Mars.”  Also, you can find gobs of information at this site.

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.

MOTION OF MARS IN OUR SKY

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 (230° Ls); however, it will not be safe to observe Mars until after April 02, 2011 when it is at least 12 degrees away from the glare of the Sun. 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 and the phase or terminator will be 37°.  The apparent declination of Mars begins at 6.6° in early 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 05, 2012.

NOTE: The Solar Elongation for Mars is the angle between the lines of sight from Earth to the Sun and from Earth to Mars.  When these lines of sight form a right triangle then Mars is at quadrature (eastern or western).   For detailed definitions and graphics for the motion of Mars in our sky see these excellent web sites: Planetary Aspects and Elongations and Configurations.

Figure 1. A heliographic chart of the orbits of Mars and the Earth showing the relative positions of both planets.  Quadrature is when Mars is directly east or west of Earth as shown.


The 2011-2012 Mars apparition begins retrogression, or retrograde motion against the background stars just over a year after from January 25, 2012 (62° Ls) through April 15, 2012 (97° 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 2).

Figure 2. 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.


2012 APPARITION CHARACTERISTICS

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.

NOTE: Ls is the planetocentric longitude of the Sun along the ecliptic of Mars' sky. 0° Ls is defined as that point where the Sun crosses the Martian celestial equator from south to north, that is the planet's northern hemisphere vernal equinox. The other Ls values that define the beginnings of Martian northern hemisphere seasons are: summer, 90° Ls; autumn, 180° Ls; and winter, 270° Ls. For Mars' southern hemisphere these values represent the opposite seasons. Distance (A.U.) - Distance from Earth to Mars in astronomical units, where one (1) A.U. equals 92,955,807.267 miles or 149,597,870.691 km.


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 2004 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 1701 UT on March 05, 2012 (79.0° Ls) with an apparent planetary disk diameter of 13.9'' at a distance of 0.673678350248 astronomical units (AU) or 62,622,315 miles (100,780,847 km).  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.  [NOTE: 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 3. A simulated view of the appearance of Mars during opposition at 2004 UT on March 03, 2012 (78.1° Ls, CM 189.8°)


The observable disk diameter of Mars will be greater than 6 arcsec from seconds November 03, 2011 [14.5° d ] (24.3° Ls) and will not fall below this value until July 20, 2012 [-3.5° d ] (142.0° 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.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 4 and 5. The 2011 and 2012 Ephemeris of Mars is tabulated on Internet in this web site.  A glossary of Terms appears at the end of this table.

Figure 4. As it approaches Earth, it will swell from a small apparent disk of 6" in November 03, 2012 to a maximum diameter on March 05, 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. Images shows at 0h UT.


Figure 5. 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 6. 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.


The Martian North Polar Region

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. The terminator shadow will cover part of polar cap until mid-December 2011 when the cap will become completely sunlit. For more detailed information on the north polar cap click to this web site.

DUST STORMS

Observations of Mars indicate that dust storms occur around the time of southern summer solstice, soon after Mars reaches perihelion. However, accurate predictions are nearly impossible to make because of the complexities and unknown variables. When a great dust storm reaches maturity, Mars' disk appears bright orange and Mars' surface features are obscured. For more detailed information on Martian dust storms on this web site.

The Martian dusty season should begin about the last week in February (241° Ls) throughout the second week of April 2011 (270° Ls). The highest probability of dust storms occurring will be on or about March 16, 2011 (255° Ls) and a sensitive area for the development of dust storms is in northwest Hellas. Also, dust clouds and storms have been observed during northern summer (105° Ls).  Another sensitive period following the “procurer” storm season will come in the middle of June (315° Ls) when observers should be alert for dust clouds in the northeast Hellas Basin, the Serpentis-Noachis region, and the Solis Lacus region. 
  
 

Table 2. CALENDAR OF EVENTS -- MARS, 2010

DATE PHYSICAL REMARKS
2011 Feb 04 Ls 229.9° Conjunction.  Mars is behind the Sun ~2.375 AU. 
2011 Mar 08 Ls 250.2°
De -24.6°
Ds -23.2°
RA 22:48
Dec -08.7°
A.Dia 3.97’’
Mars at Perihelion . Late southern spring. SPC in rapid retreat. Novus Mons smaller. Dust clouds expected over Serpentis-Hellaspontus (Ls 250 - 270). Syrtis Major narrow. Frost in bright deserts? Orographic clouds (W-clouds) possible. Elysium and Arsia Mons bright?  Frost in bright deserts? Novus Mons smaller. Note: Several "planet-encircling dust storms have been reported during this season. High probability 255° Ls.
2011 Sep 14 Ls 0°
De 13.5°
Ds 0.1°
RA 07:56
Dec 21.6°
A.Dia 4.9’’
Equinox - Northern Autumn/Southern Spring . North Polar Hood (NPH) begins to break up. North Polar Cap (NPC) should be exposed at approximately 65° Areographic latitude. ("Areo-" is a prefix often employed when referring to Mars or "Ares."). South Polar Cap (SPC) maximum diameter, subtending ~ 60.5° W. Does SPH or frost cover Hellas? Hellas should begin to clear and darken. Are W-clouds present? 
2011 Nov 03 Ls 24.3°
De 21.6°
Ds 9.9°
RA 09:54
Dec 14.5°
A.Dia 6’’
Apparition begins for observers using 4-inch to 8-inch apertures telescopes and up. Begin low-resolution CCD imaging. Views of surface details not well defined. NPC nearly static and begin erratic retreat, hood continues to dissipate. Orographic cloud over Apollinaris Petera? Windy season on Mars begins, dust clouds present? Watch for initial dust clouds in south. White patches in bright areas? Hellas bright spots? Numerous bright patches. (NPC W ~65°).
2011 Dec 17 Ls 44.7° 
De 23.5° 
Ds 17.0° 
RA 11:11
Dec 8.0°
A.Dia  8’’
North Polar Hood (NPH) breaking up, North Polar Cap (NPC) should be exposed Hellas and Argyre bright? Limb arcs increasing in frequency or intensity. Arctic hazes and clouds present? (NPC W ~52° ±4°).

2012 Jan 13 Ls 56.2°
De 23.0°
Ds 20.4°
RA 11:37
Dec 6.0°
A.Dia 10’’
Watch for "Aphelic Chill" in NPR – (usually between 60° and 70° Ls) and possible halt in thawing of NPC. Views of surface details well defined. Rima Tenuis may appear (140° and 320° Areographic meridians). Cloud activity in north increasing? (NPC W ~45° ±5°).
2012 Jan 25 Ls 61.5°
De 22.7°
Ds 21.6°
RA 11:40
Dec 6.1°
A.Dia 11.1’’
Retrogression Begins. Mars begins retrogression, or retrograde motion against the background stars nearly 355 days after conjunction, when it appears to move backwards toward the west for a brief period before, during and after opposition.    (NPC W ~42° ±4°).

2012 Feb 03 Ls 65.4°
De 22.4°
Ds 22.4°
RA 11:38
Dec 6.6°
A.Dia 12’
Watch for "Aphelic Chill" in NPR – (usually between 60° and 70° Ls) and possible halt in thawing of NPC. High-resolution CCD imaging and photography. (NPC W ~38° ±4°).
2012 Feb 14 Ls 70°
De 22.2°
Ds 23.2°
RA 11:30
Dec 7.6°
A.Dia 13’’
Mars at Aphelion . Is North Cap fairly static or entering rapid retreat phase. Watch for "Aphelic Chill" in NPR (usually between 60° and 70° Ls). NPC Rima Tenuis may appear. Antarctic hazes, hood. South polar regions becoming difficult to observe. Any signs of SPH? Cloud activity increases. Are limb arcs increasing in frequency, intensity?  (NPC W ~33° ±5°). 
2012 Mar 03 Ls 78.1°
De 21.8°
Ds 24.2°
RA 11:07
Dec 10.1°
A.Dia 13.9’’
Mars at Opposition. NPC in rapid retreat? Are limb arcs increasing in frequency, intensity. Antarctic hazes/hood. Cloud activity increases. "Aphelic Chill" in NPR should be ended. (NPC W ~28° ±4°).

2012 Mar 05 Ls 79.0°
De 21.7°
Ds 24.3°
RA 11:04
Dec 10.4°
A.Dia 13.9’’
Mars at Closest Approach. Few clouds. Limb arcs increasing in frequency or intensity. Arctic hazes and clouds present.
(NPC W ~28° ±4°).

2012 Mar 30 Ls 90°
De 21.6°
Ds 24.8°
RA 10:33
Dec 12.8°
A.Dia 12.7’’
Solstice - Northern Summer/Southern Winter. Orographic clouds over the Tharsis volcanoes – W-Cloud? Local seasonal clouds should wrap around Syrtis Major and be prominent in Lybia. Hellas white cloud and Ice-fog activity? Discrete clouds? NPC remnant? Lemuria (210° W, 82° N) detached from NPC? Any other detachments (projections at 135° W and 290° W) near NPC remnant? .   (NPC W ~20° ±4°).
2012 Apr 07 Ls 93.5°
De 21.8°
Ds 24.7°
RA 10:28
Dec 12.9°
A.Dia 12’
Orographic clouds over the Tharsis volcanoes – W-Cloud? Local seasonal clouds should wrap around Syrtis Major and be prominent in Lybia. Hellas white cloud and Ice-fog activity? Discrete clouds? Rima Tenuis may appear (140° and 320° Areographic meridians. .   (NPC W ~19° ±3°).

2012 Apr 15 Ls 97.1°
De 22.0°
Ds 24.6°
RA 10:26
Dec 12.7°
A.Dia 11.3’’
Retrogression Ends. Mars begins westward motion against the background stars. (NPC W ~19° ±3°).
 
 

2012 Apr 30 Ls 103.8°
De 22.9°
Ds 24.0°
RA 10:31
Dec 11.6°
A.Dia 10’’
Is North Cap fairly static or entering rapid retreat phase. South polar regions becoming difficult to observe. Any signs of SPH? Discrete clouds? Increasing ice-fogs and clouds? Watch for dust clouds and possible dust storms. (NPC W ~15° ±2°).
2012 May 30 Ls 117.5°
De 24.8°
Ds 21.8°
RA 11:02
Dec 7.4°
A.Dia 8’’
Is Mare Acidalium broad and dark? Bright spots in Tempe-Arcadia-Tharsis-Amazoins? "Domino effect" appears around 120 - 125° Ls. Topographic clouds increase. (NPC W ~15° ±2°).
2012 Jul 20 Ls 142.0°
De 25.1°
Ds 15.0°
RA 12:33
Dec -3.5°
A.Dia 6’’
If both polar caps are visible look for haze canopy? Clouds and frosts prominent in north. Clouds area in south. Syrtis Major broad.
 

2012 Sep 30 Ls 180° Equinox - Northern Autumn/Southern Spring South Polar Cap (SPC) maximum diameter, subtending ~ 60.5° W. Is the North Polar Hood present. Does SPH or frost cover Hellas? Hellas should begin to clear and darken. Are W-clouds present? South cap emerges from darkness of Winter. SPH thinning and forms "Life Saver Effect."
2013 Apr 17 Ls 302° Conjunction. Mars is behind the Sun ~2.430AU.