The Master Calendar of Events for Mars
("The Phenomena of the Martian Year")

Jeff Beish (Rev. 12-22-2020)
A.L.PO. Mars Section


Telescopic observations of Mars contribute to a number of areas of Mars research and, in addition, provide a useful historical record. Recognizing the need for a coordinated worldwide network of amateur planetary Mars observers, Lowell Observatory astronomer Charles F. Capen formed the ALPO Mars Section's International Mars Patrol (IMP) in 1969. The IMP, with planetary observers located around the Earth, permits 24-hour surveillance of nearly all martian longitudes. One of the amateurs' greatest strengths is the sheer number of observers providing 24-hour coverage of Mars. The IMP network has provided professionals with an "early warning system" that permits timely study of new or transient events.

Capen was able to substantiate the work many of his predecessors and explain in layman's terms the studies by professional scientists. Capen realized early in his career that Mars was indeed a changing world and was intrigued by comprehensive studies of his mentors. One such study was "The Phenomena of the Martian Year," by the world renowned astronomer, E.M., Antoniadi. This was a time and event calendar that was based on Antoniadi's 56 years of observing Mars from 1856 to 1912 [Antoniadi, 1916]. Capen also found many parallels in his own study with that of Antoniadi and began to formulate a new and more comprehensive Calendar of Martian Events from his three-decade study of Mars. Both Antoniadi and Capen demonstrated that many of the Martian seasonal events do indeed recur.

Included in the pre-apparition reports to Association of Lunar and Planetary Observers (ALPO), a table, "Calendar of Events," defines several aspects of an upcoming observing period; cardinal seasonal dates, suggested surface features to watch, possible meteorological phenomena to be seen, and many seasonal changes that had occurred in past apparitions that might reoccur. This table is in essence a prediction of the life of a Red Planet for the next year or so. It is also a reflection of Mars' past.

Having published reports before each apparition from 1968 until his death in May 1986, Capen compiled an impressive record of successful predictions for Mars. His calendar was refined several times and modified to meet the changing world of the Red Planet. His goal to educate astronomers in every aspect of Mars observing has been accomplished over and over again.

In the beginning of each appearance of Mars in the late morning sky a small group of dedicated astronomers will once again begin a virtual journey through space some 200 millions miles away to observe Mars. Some even begin earlier when Mars is barely 2 hours away from he sun or nearly 220 million miles from Earth. The Martian year is about 687 Earth days and its mean synodic period 780 mean days. So, Mars will appear in the morning sky every 780 days and begin the observing cycle again.

A telescope of at least 10 inches in diameter (25-cm) will do fine for those experienced observers who know what to expect. The Red Planet will appear as a tiny red dot just above the horizon in twilight hours just a few degrees away from the Sun. The planet may not even be visible to the naked eye, so navigational devices will be used on their machines to find this object. Some use old fashion setting circles so use modern computers to help them.

For those observers who for the first time venture out under the sky to viewing the Red Planet Mars will no doubt recoil back from the eyepiece in disbelief and bewilderment. Mars is a difficult object of study for telescopic observers to be sure. Suffice it to say Mars observing is not for the impatient person. It is observing on the fast track. Even experienced observers realize the difficulty in their quest to gaze upon Mars.

How can we contribute to mankind's knowledge of Mars? Well, it is not necessary to contribute anything to anyone else but to the satisfaction of the observer himself or herself. One may consider the words of an early member of the A.L.P.O., Joel W. Goodman, who wrote [Goodman, 1967]:

"Can it be, then, that the amateur is poorly rewarded for his efforts? If the yardstick we apply is the significance of his scientific contributions, then the answer must, in a sense, be yes. But the chase is often more rewarding that the kill. The primary motivation o the amateur is not, and never has been, his opportunity to contribute to science. The modest contributions he can make are all to the good; but his clarion call is the pure pleasure to be derived from studying the moon and planets at first hand, and from the excitement of the realization that they are largely unknown, mysterious worlds, the next frontier of man's exploration."


Mars is the only planet whose surface can be plainly seen and charted from Earth. We see features such as: four seasons, global climates, changeable weather, storm clouds of water vapor, howling dusty winds, seasonal thawing of polar ice caps, and a variety of alien, grotesque surface features which predictably change with the season, while other features mysteriously move during decades.

A column is included to represent the latitude or width of the polar caps during each 10 degrees Ls seasonal period. The latitudes for the eastern and western edges of the cap are given for the North Polar Cap (NPC) because the NPC has no appreciable offset from the rotational pole of Mars.  The widths of the South Polar Cap (SPC) are given because the SPC has an observable offset by several degrees in latitude from the present rotational pole toward 35° - 40° E, so the latitude values would be erroneous.

The Martian atmosphere is ever-changing. White water ice clouds, yellowish dust clouds, bluish limb hazes, and bright surface frosts have been studied with increasing interest in the past two decades. Clouds seem to be related to the seasonal sublimation and condensation of polar cap material. Statistical analysis indicates that discrete water ice crystal cloud activity and surface fog occurrence is significantly higher in the spring and summer of the Martian Northern Hemisphere than the same seasons for the Southern Hemisphere.

In addition to atmospheric phenomena, Mars exhibits varied and often mysterious changes of its surface. The dark blue-green "maria," called "albedo features," seem to darken during early Martian Spring in such a manner that a "wave of darkening" appears to sweep from the thawing polar cap towards the equator. This event, which occurs during each hemisphere's Spring season, lent credence to the theory that the maria were composed of vegetation, which was replenished when water flowed from the melting polar cap towards the equator. Now we know that this concept is false. In fact, the late C.F. Capen has shown that the wave of darkening is in actuality a "wave of brightening" [Capen, 1976]. The albedo features only appear to darken because the adjacent ochre desert areas have brightened during early spring. This has been confirmed by Viking Lander photos, which reveal a fresh, bright layer of dust appearing on the ground during early spring.

Regions to watch for seasonal changes are: Aonius Sinus (105 °W, 47° S), Mare Australe (340° W, 65° S), Candor- Tharsis (90° W, 10° N), Elysium-Trivium Charontis (210° W, 22° N), Hellas Basin (292° W, 50° S), Nilokeras-Lunae L. (60° W, 25° N), Pandorae Fretum (345° W, 25° S), and Syrtis Major-Aeria (300° W, 10° N).

Regions to watch for secular changes are: Acidalium Fons-Tempes C. (60° W, 58° N), Antigones Fons-Astaboras (298° W, 22° N), Mare Australe (340° W, 47° S), Candor-Tharsis (90° W, 10° N), Margaritifer S.-Hydrae S. (30° W, 02° S), Moeris Lacus.-Palus (270° W, 08° N), Nepenthes-Thoth (268° W, 08° N), Nilokeras-Lunae L. (60° W, 25° N), Nodus Laocoontis- Amenthes (245° W, 10° N), Pandorae Fretum (345° W, 25° S), Solis Lacus (85° W, 26° S), Thaumasia-Solis Lacus ("Eye-of-Mars") (90°W, 30° S), Trivium Charontis region (210° W, 22° N), and Thoana Palus (256° W, 35° N). Transient changes reports at least once: Daedalia-Claritas (115° W, 30° S), Morpheos Lacus (228°W, 37°N), Hyblaeus ["Hyblaeus Extension"] (240°W, 30°N), and Nodus Laocoontis (246°W, 25°N).

A new master listing, "The Master Calendar of Martian Events" has been setup by the ALPO Mars Section from Capen's previous listings with improvements and additions.


This table represents the accumulation of predictions that have been published in The Strolling Astronomer by the A.L.P.O. Mars Section from 1968-1969 through 2002-2004 apparitions of Mars. Important events such as cardinal seasonal dates, observed seasonal and secular surface changes, and meteorological phenomena detailed for each 10 degree period from the Northern Spring/Southern Autumn Equinox (0° - 89° Ls), Northern Summer/Southern Winter Solstice (90° - 179° Ls), Northern Autumn/Southern Spring Equinox (180° - 269° Ls), and Northern Winter/Southern Summer Solstice (270° - 359° Ls).
  Equinox - Northern Spring/Southern Autumn. North Polar Hood (NPH) breaking up, North Polar Cap (NPC) should be exposed. ("Areo-" is a prefix often employed when referring to Mars or "Ares.") 
NPC~60 - 65: see NOTE 2 & 3
North Polar Hood (NPH) breaking up and North Polar Cap (NPC) should be exposed.  Hellas and Argyre bright? 
NPC~60 - 65
NPC nearly static or entering erratic retreat, hood dissipating?  Orographic cloud over Apollinaris Petera?
NPC~60 - 65
Limb clouds and hazes should start to increase. 
NPC ~65  ±4
Few clouds. Limb arcs increasing in frequency or intensity? Arctic hazes and clouds?  Dust clouds in NPR?
NPC ~68 ±4
Continue NPC measurements. Is North Cap fairly static or entering rapid retreat phase. South polar regions becoming difficult to observe. Any signs of South Polar Hood (SPH)? 
NPC ~70 ±2
Micrometer measurements of NPC possible. Watch for "Aphelic Chill" in North Polar region (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 ~74 ±1
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). 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 ~77 ±3
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 ~81 ±3
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 ~83 ±2
Is North Cap fairly static or still in retreat phase? South polar regions becoming difficult to observe. Any signs of SPH? Discrete clouds? Increasing ice-fogs and clouds? Dust at 105° Ls?
NPC ~83 ±1
NPC still retreating? 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 ~83 ±1
Is Mare Acidalium broad and dark? Bright spots in Tempe-Arcadia-Tharsis-Amazoins? "Domino effect" appears around 120° - 125° Ls. Topographic clouds increase.
NPC ~84 ±1
White clouds and ice-fogs frequent. Syrtis Major and Mare Acidalium broad and dark? °). Orographic cloud over Olympus Mons.
If both polar caps are visible look for haze canopy? Clouds and frosts prominent in north. Clouds area in south. Syrtis Major broad.
  Mid-summer. Northern clouds frequent. Syrtis Major broad. Are both polar hoods visible?
  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?
  Late southern winter, SPH present and edge of NPH visible. Hellas frost covered? Are W-clouds present?
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?"  Be aware of early dust storms around 184° Ls due to early storms in 2001 and 2018.
SPC should be free of its hood, large and bright. Possible W-clouds in Tharsis-Amazonis. Syrtis Major shrinks or fading on eastern border. NPH bright. White areas brighter? White areas brighter? Within Hellas the features Zea Locus and Alpheus darkening? Mare Hadriacum (265°W, 40°S) and Yaonis Regio (318°W, 43°S) connected the canal Peneus?
SPC ~ 54 ±6: see NOTE 1 & 3
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 ~ 49 ±4
SPC develops dark Magna Depressio at (270°W, 80°S). Syrtis Major narrows rapidly. W-clouds? At 215°Ls Rima Australis (a dark rift) appears connected with Magna Depressio from 20° to 240° longitude; and SPC develops bright projection at 10° - 20° longitude in Argenteus Mons (10°-20°W). Dust cloud in Serpentis-Hellaspontus or Noachis-Hellas? Syrtis Major very narrow? 
SPC ~ 45 ±5
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 ~38 ±9
Rapid regression of SPC.. Bright elongated Novissima Thyle reaches from SPC and becomes the isolated Novus Mons ("Mountains of Mitchel"). Rima Australis broadens, and Magna Depressio becomes dusky feature. Eastern Syrtis Major retreats. North Polar Hood prominent.
SPC ~ 32 ±7
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 241° Ls.
SPC ~ 26 ±4
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 Arisa Mons bright?  Note: Several "planet-encircling dust storms have been reported during this season. High probability for dust clouds at 255° Ls. 
SPC ~ 21 ±2
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. Syrtis Major beginning to narrow.
SPC ~17 ±2
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 ~16 ±2
NPH extends 50° N? White clouds rare. Dust storm? Frost patches? Dust storms visible at 285° Ls (Martin & Zurek).
SPC ~ 10 ±2
Look for orographic clouds over the Tharsis volcanoes. Orographic cloud over Arsia Mons? W-Cloud?  SPC small.
SPC ~10  ±0.8
White areas? Orographic clouds over the Tharsis volcanoes. W-Cloud? Orographic cloud over Arsia Mons? SPC very small, difficult to see. 
Edom bright? Is SPC remnant visible in mid-summer? Orographic cloud over Arsia Mons? Topographic cloud over Libya? High probability of dusty storm at 315° Ls. Planet encircling dust storm in November 2020 (308° - 323° Ls).
Wave or frontal cloud activity from NPR? Bright spots in Hellas? Orographic cloud over Arsia Mons? Topographic cloud over Libya? Topographic cloud over Edom?
  Hellas Ice-fog activity? Topographic cloud over Libya? Topographic cloud over Edom?
  NPC large hood present. W-Cloud? Orographic cloud over Arsia Mons? Topographic cloud over Libya? Topographic cloud over Edom?
  NPC large hood (NPH) present. Discrete (white) clouds and white areas should be seen. Syrtis Major begins to expand to its east. Topographic cloud over Libya?

          NOTE 1:  Based on ALPO Mars Section South Polar Cap Measurements from 1986 – 2005.
          NOTE 2:  Based on ALPO Mars Section North Polar Cap Measurements from 1980 – 1999.
          NOTE 3: The NPC/SPC column represents the north polar cap as a function of latitude. The since the SPC has an observable offset
                           from the present rotational pole toward 35° - 40° E the width are presented.


Antoniadi, E.M., "The Phenomena for the Martian Year," BAA Memoirs, Vol. XX, 1916, pp. 482-486.

Capen, C.F., "Observing Mars – V: The 1973-74 Martian Apparition," The Strolling Astronomer, Vol. 24, Nos. 7-8, October 1973, pp. 129-136.

Capen, C.F., "Martian Albedo Feature Variations with Season: Data of 1971 and 1973," ICARUS, 28, 213-230, 1976.

Goodman, Joel W., "Reflections on Amateur Lunar and Planetary Observational Astronomy and the Role of the A.L.P.O.," The Strolling Astronomer, Vol. 20, Nos. 7-8, September 1967, pp. 110-111.

Martin, L. J. and R. W. Zurek (1993). "An Analysis of the History of Dust Activity on Mars." Journal of Geophysical Research, Vol. 98, no. E2, pp. 3221-3246.