THE 2024-2025 APHELIC APPARITION OF MARS
By: Jeffrey D. Beish (04-SEP-2023)
   

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 (2018-2022), 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 November 18, 2023 (0447UT); however, it will not be safe to observe Mars until after December 29, 2023 when it is at least 12 degrees away from the glare of the Sun.  

The apparent declination of Mars begins at 21.6° in early August 2024 the constellation Ophiuchus and will descend south into the constellations Sagittarius, Capriconus, Aquarius and Pisces until July 10, 2022.  After that Mars will be positioned within Aries until August 10^th when it moves into Taurus . Mars will be south of the celestial equator throughout the apparition until May 30, 2022 and begin climbing north of the celestial equator the next day. 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 29, 2025.  By August 06, 2024, an ‘0.9’ visual magnitude Mars will be seen rising early in the morning sky in the constellation Aquarius and by October 14, 2024  will be at western quadrature with the phase defect or terminator of 41.0°.

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 2024-2025 apparition of Mars begins retrogression, or retrograde motion against the background stars eleven months after conjunction on December 06, 2024 (11.6° Ls) and continues through February 24, 2025 (48.4° 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 Taurus.   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 2024-2025 Apparition of Mars. Original graph prepared by C.F. Capen and modified by J.D. Beish.

2025 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 2025 Mars apparition is considered Aphelic because the orbital longitude at opposition will be 39.1° from the aphelion longitude of 70° Ls and 219.1° 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.

Closest approach occurs at 1338 UT on January 12, 2025 (29.2° Ls) with an apparent planetary disk diameter of 14.6'' at a distance of 0.6422825 astronomical units (AU) or 59,703,891 mi (96,084,099-km).   During closest approach in 2025 the apparent diameter of Mars will be 2.6 arcsec smaller than it was at the same period in 2022; the declination will be virtually the same only 0.2 degrees lower in the sky - good for observing the Red Planet for observers in the northern and southern hemispheres of Earth.  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 14 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 0232 UT on January 16, 2025 (30.9° Ls) with an apparent planetary disk diameter of 14.5 arcsec. Mars will remain visible for 10 months after opposition and then become lost in the glare of the Sun around November 24, 2025; as it approaches the next conjunction (January 09, 2026). The cycle is complete in 780 Earth days.

Figure 3. A simulated view of the appearance of Mars during opposition at 0232 UT on January 16, 2025 (30.9° Ls , CM 353.5°)  

The observable disk diameter of Mars will be greater than 6 arcsec from August 05, 2024 [21.56° δ] (306.6° Ls) and will not fall below this value until May 17, 2025 [18.5° δ] (84.3° Ls), lasting nearly 9.4 months or 138 degrees Ls.  Imaging by CCD devices may begin with a disk diameter of 4 arcsec or more, commencing on or about January 18, 2024.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 4 and 5. The 2024-2025 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 August 05, 2024 to a maximum diameter of 14.6” at closest approach on May 17, 2025, and then shrink as it moves away.   Images shown at 0h UT.

Figure 5. Graphic Ephemeris of Mars during the2024-2025 apparition from August 05, 2024 through May 17, 2025.    Opposition (30.8° Ls) and 6 arcsec apparent diameter range are 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, 71° when Mars is at aphelion, and 90° at the summer solstice of the northern hemisphere 251° when Mars is at perihelion, and 180° is northern autumn.

Figure 6. Graphic Ephemeris of Mars from August 05, 2024 through May 17, 2025. Opposition (30.8° Ls) and 6 arcsec apparent diameter range are 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 AND SOUTH POLAR REGIONS

Astronomers will have an excellent view of the prominent north polar cap during the 2025 apparition as it will be tilted earthward during 2024 and 2025. From the first week in August 2024 the Martian North Polar Region (NPR) will be positioned to be seen from the Earth and will remain so throughout the observable apparition. By December 24, 2024 (20° Ls) the NPC should be free of its hood and completely sunlit. Micrometer measurements can be easily be made until late April 2025. For more detailed information on the north polar cap click to this web site.

DUST STORMS

Observers should be aware that massive, planet-encircling storms usually occur in the southern hemisphere summer and usually in sensitive areas for the development of dust storms are in the south of Acidalium Mare, Chryse, Erythraeum Mare, Ophir and northeast Solis Lacus. While these events are nearly impossible to predict our studies show that the Martian dusty season should be ongoing from the beginning of the apparition through the end with the highest probability around in mid-May (225° Ls) and again peaking on or about August 21, 2024 (315° Ls) often starting in northwest Hellas. Also,observers should be alert for dust clouds in the northeast Hellas Basin, the Serpentis-Noachis region, and the Solis Lacus region.

If the Red Planet behaves as it did in 2001 and 2018, then 2024-2025 may be a time when Mars may be very dusty indeed! For more detailed information on For more detailed information on Martian dust storms on this web site Martian dust storms on this web site.