THE 2028-2029 APHELIC APPARITION OF MARS
By: Jeffrey D. Beish (25-OCT-2020)
   

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) 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 (2020-2027), observers began to take CCD images when Mars was only 30 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 March 21, 2028 at 09:59UT (275.5° Ls); however, it will not be safe to observe Mars until after May 15, 2028 when it is at least 12 degrees away from the glare of the Sun.

The apparent declination of Mars begins at 15.4° in mid-May 2028 in the constellation Aries and will remain above the celestial equator through the first week of January 2029. After January 06 the declination of Mars will hover between +/-6 degrees until mid-July when it will begin to descend southward into Taurus, Gemini, Cancer, Leo and Virgo by the first week in December. The apparent diameter of Mars will then be at 6 second of arc and will start the traditional visual observing time during the 2028/2029 apparition. This is good news for those observing in the Northern and Southern Hemispheres because Mars will be seen close to the celestial equator for much of the apparition. The declination of Mars will continue to descend south of the celestial equator throughout the remainder of the apparition.  

By December 21, 2028 a ’0.8’ visual magnitude Mars will be seen rising early in the morning sky in the constellation Virgo and it will be at western quadrature with the phase defect or terminator at 36.3°. 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 2028-2029 Mars apparition begins retrogression, or retrograde motion against the background stars eleven months after conjunction from February 14, 2029 (82.1° Ls) through May 05, 2029 (118° 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 in 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 2029 Aphelic Apparition of Mars. Original graph prepared by C.F. Capen and modified by J.D. Beish.

2029-2029 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 2029 Mars apparition is considered Aphelic because the orbital longitude at opposition will be only 29.5° 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 twelve 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 nearly six weeks after that retrogression begins. Opposition will occur at 0743 UT on March 25, 2029 (99.5° Ls), with an apparent planetary disk diameter of 14.4 arcsec. Mars will remain visible for a year after opposition and then become lost in the glare of the Sun again (April 06, 2030) as it approaches the next conjunction (1050UT, May 25, 2030). The cycle is complete in 780 Earth days.

Closest approach occurs at 1256 UT on March 29, 2029 (101.2° Ls) with an apparent planetary disk diameter of 14.5’’ at a distance of 0.6472225 astronomical units (AU) or 60,163,090 miles (96,823,107 km). During closest approach in 2029 the apparent diameter of Mars will be 0.7 arcsec larger than it was at the same period in 2027; however, it will be 13.8 degrees lower in the sky - not great for observing the Red Planet. 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.

FFigure 3. A simulated view of the appearance of Mars during opposition at 0743 UT on March 25, 2029 (99.5° Ls, CM 112.3°)  

The observable disk diameter of Mars will be greater than 6 arcsec from November 27, 2028 [19.2° δ] (47.5° Ls) and will not fall below this value until September 01, 2029 [-17.3° d] (178.6° Ls), lasting 9 months or 131 degrees Ls. This apparition will follow a similar profile to the 2012 apparition of Mars. Imaging by CCD devices may begin with a disk diameter of 4 arcsec or more, commencing on or about July 06, 2028.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 4 and 5. The 2028-2029 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 27, 2028 to a maximum diameter on September 01, 2029, and then shrink as it moves away. Closest approach occurs on March 29, 2029 (101.4° Ls). Images shown at 0h UT.

Figure 5. Graphic Ephemeris of Mars during the 2028-2029 apparition from November 27, 2028 through September 01, 2029. Opposition (99.5° Ls) and 6 arcsec apparent diameter range arc indicated. Plot illustrates the Declination (solid line), the latitude of the Sub-Earth point (De) or the apparent tilt (dashed line) in areocentric degrees, and the latitude of the Sub-Solar point (dotted 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 November 27, 2028 through September 01, 2029. Opposition (99.5° Ls) and 6 arcsec apparent diameter range arc indicated. 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 REGIONS

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 entire apparition. The terminator shadow will cover part of polar cap until late-November 2028 when the cap will become completely sunlit. For more detailed information on the 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 Martian dust storms web site.

Dust clouds and storms have been observed during northern summer April 06-07, 2029 (105° Ls).