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 (2010-2016), 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 with the Sun on July 26, 2017 (38.9° Ls); however, it will not be safe to observe Mars until after September 02, 2017 when it is at least 12 degrees away from the glare of the Sun.

The apparent declination of Mars begins at 13.5° in early September 2017 in the constellation Leo and during mid-October will descend south into the constellations Virgo. Two weeks later Mars will be south of the celestial equator throughout the apparition until January 02, 2019 when Mars will begin to ascend in declination. 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 reaching -23.6° by March 26, 2018 and will remain below -20° until October 16, 2018.  After that Mars will cross from the constellation Capricornus into Aquarius in early-November and ascend northward for the remainder of 2018 to cross north of the celestial equator in January 2019.

By March 24, 2018, a ‘0.4’ visual magnitude Mars is seen rising early in the morning sky in the constellation Sagittarius, it will be at western quadrature  and the phase or terminator will be at 40.2°.  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 2018 apparition of Mars begins retrogression, or retrograde motion against the background stars eleven months after on June 28, 2018 (201.1° Ls) and continues through August 27, 2018 (238.2° 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 Capricornus.

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 2018 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 2018 Mars apparition is considered Perihelic because the orbital longitude at opposition will be 31.1° from the longitude of 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.

The 2018 Perihelic Apparition of Mars will prove to be one of the most favorable since the 2003 apparition when the Red Planet came closest to Earth in 59,635 years (the year 57,617 B.C.). Of the 56 oppositions of Mars from February 22, 1901 through July 27, 2018, only 15 can be considered as favorable apparitions. We define a "favorable apparition" as one that offers the observer the best possible aspects for observing the planet visually and/or for recording it electronically. The length of time Mars remains in good position for observing is considered. We might select an apparition in which Mars reaches its largest apparent size, or when it is highest in the sky, not only for observers in the Northern Hemisphere but for those in the Southern Hemisphere as well. We might even consider the relative weather conditions where the majority of observers live.

From the above factors the ALPO Mars Section has selected the 2018 apparition to be among the 15 favorable. The aspects considered were the planet's declination (δ), its photographic or photoelectric intensity, and its apparent size during any particular apparition. From these considerations, it appears that the 1956 apparition (-9.9° δ) with an apparent diameter of 24.8" meets all the above requirements and should be considered the best. Even though Mars presented a larger apparent diameter of 25.13'' in 2003, its low -15.7° declination places that year in second place. The Mars Section has concluded that 2003 will be remembered as the second best apparition the 20th century, at least for the majority of observers.

Mars will exceed 24'' in diameter between July 23rd and August 9th, 2018. This is 97 percent of the maximum of 25.13'' diameter attained during the last of the "favorable" apparitions, which occurred in 2003. During the 2003 apparition, Mars came within 34.6 million miles to Earth, closer than at any time in over nearly sixty thousand years! The Red Planet will be only 1.2 million miles further away in 2018! What makes the 2018 apparition so favorable is that Mars will be less than one second of arc smaller than it was in 2003, but will be 9.8 degrees lower in the sky for observers in the northern hemisphere; however, Mars will be favorably placed for observers in the southern hemisphere of Earth.

Closest approach occurs at 0751 UT on July 31, 2018 (221.4° Ls) with an apparent planetary disk diameter of 24.3'' at a distance of 0.3849629 astronomical units (AU) or 35,785,537 mi (57,590,630-km).  During closest approach in 2018 the apparent diameter of Mars will be 5.7 arcsec larger than it was at the same period in 2016 and it will be 4.4 degrees higher 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.

A simulated view of the appearance of Mars during opposition at 0507 UT on July 27, 2018 (218.9° Ls, CM 143.9°)

The observable disk diameter of Mars will be greater than 6 arcsec from February 12, 2018 [-21.4° δ] (128.3° Ls) and will not fall below this value until February 06, 2019 (336.4° Ls), lasting 11.9 months or 208 degrees Ls.  Imaging by CCD devices may begin with a disk diameter of 4.3 arcsec or more, commencing on or about December 05, 2017.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 4 and 5. The 2017-2019 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 February 12, 2018 to a maximum diameter on July 31, 2018, and then shrink as it moves away.  Closest approach occurs on July 31, 2018 (Opposition July 27, 2018).  Images shown at 0h UT.

Figure 5. Graphic Ephemeris of Mars during the 2018 apparition from February 13, 2018 through February 05, 2019.  Opposition (218.9° 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 251° when Mars is at perihelion, and 180° is northern autumn.

Figure 6. Graphic Ephemeris of Mars from February 13, 2018 through February 05, 2019. Opposition (218.9° 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.

Astronomers will have a view of the Martian South Polar Region (SPR) will be tilted toward the Earth and will remain so throughout the apparition when it reaches 0° De on March 04, 2018 and should be free of its hood. For more detailed information on the south polar cap click to this web site.

Observations of Mars indicate that major dust storms tend to be more frequent when Mars is closest to the Sun – during southern hemisphere spring and summer. While predicting these events is nearly impossible to make our studies show that the Martian dusty season should begin about the first week in April (241° Ls) throughout the middle of October 2018 (270° Ls). The highest probability of dust storms occurring will be on or about September 23, 2018 (255° Ls) and a sensitive area for the development of dust storms is in northwest Hellas.

Massive, planet-encircling storms usually occur in southern hemisphere summer and that will come by the end of December (315° Ls).  Observers should be alert for dust clouds in the northeast Hellas, the Serpentis-Noachis region, and the Solis Lacus region. If the Red Planet behaves as it did in 2001 and 2003, then 2018 may be a time when Mars may be very dusty indeed! For more detailed information on Martian dust storms on this web site.