THE 2015-2016 APHELIC APPARITION OF MARS
By: Jeffrey D. Beish (06-12-2014)
 

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 (2001-2012), 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 with the Sun on June 14, 2015 (357.7° Ls); however, it will not be safe to observe Mars until after July 27, 2015 when it is at least 12 degrees away from the glare of the Sun.

The apparent declination of Mars begins at -9.6° in early January 2016 in the constellation Virgo and descends south of the celestial equator throughout January, February and the first week of March in the constellation Libra. This is not good news for those observing in the Northern Hemispheres because Mars will be seen fairly low in their sky during the entire apparition. Good news for southern hemisphere observers however. The declination of Mars will continue to descend south of the celestial equator until May 10, 2016 then lingers at around -21.8° through opposition and closest approach.  After that Mars descends southward for the remainder of 2016 and crossing from the constellation Libra into Scorpius during the early-August.

By February 07, 2016, a ‘0.7’ visual magnitude Mars will be seen rising early in the morning sky in the constellation Libra and it will be at western quadrature with the phase defect or terminator at 37°.  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 2015-2016 apparition of Mars begins retrogression, or retrograde motion against the background stars ten months after conjunction on April 17, 2016 (138.6° Ls) and continues through June 29, 2016 (176.8° Ls).  Each night for this brief period of time; before, during and after opposition the Red Planet will appear to move backwards toward the western sky in the Virgo.

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 2014 Aphelic Apparition of Mars. Original graph prepared by C.F. Capen and modified by J.D. Beish.


2015-2016 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 2016 Mars apparition is considered Transitional (between Aphelic and Perihelic) because the orbital longitude at opposition will be 86.3° from the aphelion longitude of 70° Ls and 93.7° Ls from perihelion (250° 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 11 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 retrogression begins. Opposition will occur at 1111 UT on May 22, 2016 (156.5° Ls) with an apparent planetary disk diameter of 18.4 arcsec. Mars will remain visible for more than twelve months after opposition and then become lost in the glare of the Sun around June 17, 2017 as it approaches the next conjunction (July 27, 2017). The cycle is complete in 780 Earth days.

Closest approach occurs at 2136 UT on May 30, 2016 (161.0° Ls) with an apparent planetary disk diameter of 18.6’’ at a distance of 0.503222792 astronomical units (AU) or 46,777,481 miles (75,281,058 km).  During closest approach in 2016 the apparent diameter of Mars will be 3.4 arcsec larger than it was at the same period in 2014; however, it will be 16.5 degrees lower in the sky – not quite as good for observing the Red Planet for observers in the northern hemisphere.  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.

3. A simulated view of the appearance of Mars during opposition at 1111 UT on May 22, 2016 (156.5° Ls, CM 341.0°)


The observable disk diameter of Mars will be greater than 6 arcsec from January 13, 2016 [-11.8° d ] (94.4° Ls) and will not fall below this value until December 22, 2016 (284.8° Ls), lasting 11 months or 190 degrees Ls.  Imaging by CCD devices may begin with a disk diameter of 4.3 arcsec or more, commencing on or about November 01, 2015.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 4 and 5. The 2015 and 2016 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 13, 2016 to a maximum diameter on May 30, 2016, and then shrink as it moves away.  From January 2016 through December 2016 are the prime observing months. Images shown at 0h UT.


Figure 5. Graphic Ephemeris of Mars during the 2014-2016 apparition from January 13, 2016 through December 20, 2016.   Opposition and 6 arcsec apparent diameter range arc indicated.  Plot illustrates the Declination (black line),   the latitude of the Sub-Earth point (De) or the apparent tilt ( brown line ) in areocentric degrees, and the latitude of the Sub-Solar point ( green 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 13, 2016 through December 20, 2016.  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 NORTH POLAR REGION

Astronomers will have a view of both polar regions during the next apparition. From the first week in December 2015 the Martian North Polar Region (NPR) will be tilted toward the Earth and will remain so until September 25, 2016 when it reaches 0° De and should be free of its hood; however, Mars will be too small to begin micrometer measurements until January 2016. By the end of September2016 the south polar cap will tilt toward Earth.   For more detailed information on the north polar cap click to this web site. Information on the south polar cap click to this web site.

DUST STORMS

Observations of Mars indicate that dust storms occur around the time of northern summer solstice (90° - 105° Ls). 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.

SPECIAL EVENTS

For those interested in catching a glimpse of possible "flares" from the surface of Mars (Edom) there will be a period when it will be possible to be seen when the De and Ds are coincident will be on or about May 21, 2016. The last time this event was recorded was during June 07, 2001 when the De = 1.8° and Ds = 2.5° and Mars was situated favorably in the sky for observers to record this rare event. The De and Ds will be very close together in this apparition; however, they will be slightly higher (8.4° and 7.6° respectively) than in 2001 when the "flares" were seen. Detailed report of the 2001 event (Dobbins, Thomas A. and Sheehan, William (2001), "The Martian-Flares Mystery," Sky and Telescope, Vol. 101, No. 5, May, pp115-123) and "Solving the Martian Flares Mystery," Dobbins and Sheehan, ALPO Web Site.  See table below for dates when De - Ds +/- 1.0°:

First Period: Di = 18.2" to 18.3"

            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
 

Table 2. CALENDAR OF EVENTS -- MARS, 2015-2016

DATE PHYSICAL REMARKS
2015 Jun 14 Ls 358° Conjunction. Mars is behind the Sun ~2.568 AU.
2015 Jun 19 Ls 0° 
De 0.8° 
Ds 0.1° 
RA 05:43 
Dec  24.0° 
A.Dia 3.6’’
Equinox - Northern Spring/Southern Autumn. 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.")
2015 Nov 19 Ls 70° 
De 24.8° 
Ds 23.6° 
RA 12:15
Dec -0.1° 
A. Dia 4.5’’
Mars at Aphelion. Is NPC 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  NPC width ~31° ±3°
2016 Jan 03 Ls 90° 
De 19.7° 
Ds 25.2° 
RA 13:52
Dec -10.0° 
A. Dia 5.6’’
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 Width ~18° ±4°.
2016 Jan 13 Ls 94.4° 
De  18.1° 
Ds  25.1° 
RA 14:13 
Dec -11.8° 
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. Novus Mons reduced to a few bright patches and soon disappears. 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. 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 Width ~17° ±4°). 
2016 Feb 08 Ls 106.1° 
De  13.5° 
Ds  24.2° 
RA 15:05 
Dec -15.9° 
A.Dia  7.2’’
Mars at quadrature. NPC in rapid retreat? Are limb arcs increasing in frequency, intensity? Antarctic hazes, hood? Cloud activity high? Tempe-Arcadia-Tharsis-Amazonis regions bright in a pattern appearing as the "domino effect." Discrete clouds? 
NPC width ~15° ±3°
2016 Feb 21 Ls 112.0° 
De 11.2° 
Ds 23.3° 
RA 15:29 
Dec -17.5° 
A. Dia  8’’
NPC in rapid retreat? Are limb arcs increasing in frequency, intensity? Antarctic hazes/hood. Cloud activity high. Tempe-Arcadia-Tharsis-Amazonis regions bright in a pattern appearing as the "domino effect." Discrete clouds? 
(NPC Width ~15° ±2°). 
2016 Mar 16 Ls 123.1° 
De  7.7° 
Ds 20.9° 
RA 16:06 
Dec -19.7° 
A. Dia  10’’
Is Mare Acidalium broad and dark? Bright spots in Tempe-Arcadia-Tharsis-Amazoins? "Domino effect" appears around 120° - 125° Ls. Topographic clouds increase. (NPC Width ~14° ±3°). 
2016 Apr 02 Ls 131.2° 
De  6.2° 
Ds 18.7° 
RA 16:23 
Dec -20.7° 
A.Dia 12’’
White clouds and ice-fogs frequent. Syrtis Major and Mare Acidalium broad and dark?  Orographic cloud over Olympus Mons. 
(NPC Width ~13° ±2°). 
2016 Apr 17 Ls 138.6° 
De  5.9° 
Ds 16.4° 
RA 16:29 
Dec -21.3° 
A.Dia 14.1’’
Retrogression Begins. Mars begins retrogression, or retrograde motion against the background stars 10 months after conjunction, when it appears to move backwards toward the west for a brief period before, during and after opposition.  Clouds and frosts prominent in north. Clouds area in south. Syrtis Major broad. (NPC Width ~13° ±1°).
2016 May 22 Ls 156.3° 
De  10.4° 
Ds   9.9° 
RA 15:58 
Dec -21.7° 
A.Dia 18.4’’
Mars at Opposition. Are both polar hoods visible? SPH present and edge of NPH visible.  Hellas frost covered?  Are W-clouds present? Is Morpheos Lacus (228°W, 37°N) prominent? Are topographic clouds prominent in Libya, Aeria, Moab, Edom, and Candor?
2016 May 30 Ls 161.0° 
De 11.9° 
Ds  8.2° 
RA 15:46 
Dec -21.5° 
A.Dia 18.6’’
Mars at Closest Approach. Is Mare Acidalium broad and dark? Bright spots in Tempe-Arcadia-Tharsis-Amazoins? "Domino effect" appears around 120° - 125° Ls. Topographic clouds increase. 
2016 Jun 29  Ls 176.8° 
De 15.4° 
Ds  1.3°
RA 15:19 
Dec -21.0° 
A.Dia 16.6’’
Retrogression Ends. Mars begins westward motion against the background stars. South Polar Cap (SPC) maximum width.   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"? 
2016 Jul 05 Ls 180° 
De  15.4° 
Ds  -0.1° 
RA 15:20 
Dec -21.2° 
A.Dia 15.9’’
Equinox - Northern Autumn/Southern Spring. South Polar Cap (SPC) maximum width.   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"? 
2016 Aug 12 Ls 202.3° 
De 11.1° 
Ds -9.3° 
RA 16:04 
Dec -23.7° 
A.Dia 12’
SPC shrinking. Syrtis Major darkens and continues to shrink. W-clouds possible. Surface details increasing in contrast Hellas the features Zea Locus and Alpheus dark? SPC Novissima Thyle (300°-330°W) projection present?  (SPC width ~52° ±6°).
2016 Sep 08 Ls 218.7° 
De  4.7° 
Ds -15.4° 
RA 17:06 
Dec -25.5° 
A.Dia 10’’
Bright SPC projection Novissima Thyle  (300°W - 330°W) Areographic longitude. Dark rift Rima Augusta connected from 60° to 270° longitude. Rima Australis visible in SPC (290°-350°W)? W-clouds possible. SPC bright projection Argenteus Mons (10°W-20°W). SPC Dust clouds in Serpentis-Hellespontus, in Hellas or Noachis?   (SPC width ~44° ±3°).
2016 Oct 18 Ls 243.8° 
De  -7.3° 
Ds -22.5° 
RA 19:01 
Dec -24.8° 
A.Dia 8’’
SPC rapid retreat. Novus Mons small, bright, and high-contrast. Rima Australis widens. SPC isolated bright spot at 155° longitude? Any white patches near -20° latitude may brighten. Atmosphere of Mars very clear during Ls 240°- 250°. Occasional morning limb hazes. Dust clouds? Note: Several "planet-encircling dust storms have been reported during this season at 24° Ls. (SPC width ~28° ±3°).
2016 Oct 28 Ls 250° 
De -10.4° 
Ds  -23.6° 
RA 19:32 
Dec -23.8° 
A.Dia 7.6’’
Mars at Perihelion. SPC in rapid retreat. Novus Mons smaller. Dust clouds expected over Serpentis-Hellaspontus (Ls 250° - 270°). Syrtis Major beginning to narrow. Frost in bright deserts? Orographic clouds (W-clouds) possible. Elysium and Arsia Mons bright?    Note: Several "planet-encircling dust storms have been reported during this season.  High probability 255° Ls. (SPC width ~ 24° ±3°).
2016 Nov 29 Ls 270° 
De -19.2° 
Ds  -25.2° 
RA 21:10 
Dec -17.8° 
A.Dia 6.6’’
Solstice - Northern Winter/Southern Summer. W-clouds present? NPH extends 50° N? Decreased number of White clouds. "Syrtis Blue Cloud"? White areas in deserts? Dust clouds in south until 270° Ls?  Watch for planetary system clouds bands. Orographic cloud over Arsia Mons? Syrtis Major is narrow.  (SPC width ~ 17° ±2°).
2016 Dec 18 Ls 282.3° 
De  -23.1° 
Ds  -24.6° 
RA 22:05 
Dec -12.9° 
A.Dia 6’’
NPH extends 50° N? White clouds rare. Dust storm? Frost patches? Dust storms visible at 285° Ls (Martin & Zurek).
(SPC width ~ 12° ±2°).
2017 Jul 27 Ls 38.5° Conjunction. Mars is behind the Sun ~2.65AU.