Your ASO Guide to Observing MARS the Red Planet

by  P. Clay Sherrod
Arkansas Sky Observatory
(ADAPTED AND ABRIDGED FROM "A Complete Manual of Amateur Astronomy", by P. Clay Sherrod, DOVER BOOKS, Spring 2003)

    Since the Viking ( ) and Mariner ( ) spacecraft visited the vicinity of the mysterious planet Mars, some of the wonder and mystique have disappeared from our attitudes toward the red planet. We have now closely examined the surface, and it appears that there are no creatures there. Indeed, not even the basic organics necessary for life exist in the Martian environment. Yet it appears that Mars at one time was quite active both geologically and meteorologically, considerably more so than at present.
    Near the beginning of the twentieth century, astronomer Percival Lowell ( ) had the theory, based largely on the ideas of Italian astronomer Schiaparelli, that Mars was a dying world, one in which its inhabitants were starving and dehydrating from the lack of water.  Lowell theorized that - knowing that the Martian spring and winter would result in melting the Martian polar caps - the inhabitants had built a vast network of canals to take the life-giving moisture of those caps into the arid equatorial regions of Mars.  We now know that Mars does not have canals and that there are no inhabitants who wait eagerly for the advent of spring. Yet Lowell was correct about one point of his theory - Mars is, indeed, a dying world.
    The processes we see today on Mars are the result of phenomena that occurred only yesterday in the life of our solar system; many of the processes continue to this day, only on a considerably smaller scale. Massive volcanoes not yet eroded by the winds of Mars still loom on the Martian surface.  And still fresh canyons appear as the result of the activity in the recent past.
    It is this lure of the similarities of features on this earth that keeps writers, poets, movie-makers and even astronomers captivated by the Red Planet.

    Most favorable apparitions will place Mars similarly favorable to that of 1924....when folks on earth still longed to know the details about the "inhabitants" of that mysterious world.  The following table (data courtesy N.A.S.A.) provides recent oppositions of Mars, its Right Ascension and Declination, apparent disk size in seconds of arc and the distance of the planet from earth in astronomical units (1 A.U. = about 92.7 million miles).
    1995 Feb 12     09h 47m     +18° 11'     13.8"     0.676
    1997 Mar 17     11h 54m     +04° 41'     14.0"     0.661
    1999 Apr 24     14h 09m     -11° 37'     16.2"     0.583
    2001 Jun 13     17h 28m     -26° 30'     20.5"     0.456
    2003 Aug 28     22h 38m     -15° 48'     25.1"     0.373
    2005 Nov 7     02h 51m     +15° 53'     19.8"     0.470
    2007 Dec 28     06h 12m     +26° 46'     15.5"     0.600
    2010 Jan 29     08h 54m     +22° 09'     14.0"     0.664
    2012 Mar 3     11h 52m     +10° 17'     14.0"     0.674
    2014 Apr 8     13h 14m     -05° 08'     15.1"     0.621
    2016 May 22     15h 58m     -21° 39'     18.4"     0.509
    2018 Jul 27     20h 33m     -25° 30'     24.1"     0.386
    Note that the apparitions of August 28, 2003 and July 27, 2018 are presenting Mars with nearly as large an extended disk as possible.  The size of 25.1" for the outstanding 2003 apparition afforded a wonderful view of surface detail, cloud formations, melting of the polar caps and much more exciting developments as described in detail in this Arkansas Sky Observatory MARS GUIDE.
    ONE interesting note, however, separates the 2003 opposition to many other favorable ones before and after.  Take a look at the declination of the planet in that year....minus 15 degrees, considerably higher in the sky for northern latitudes than any favorable placement since 1924, when the apparent size was nearly identical to that of 2002, yet it was slightly lower in southern skies for northern observers.  Thus, if you are an observer in the Northern hemisphere, in such favorable oppositions, Mars shows a very large disk, fairly high in the sky and only about 35 million miles away from the base of your telescope.

    Because of the many uncertainties that still exist regarding the visible phenomena of the Martian surface and atmosphere, Mars continues to appeal to the amateur astronomer. In addition, we can rationalize in our human way that the spacecraft may "have missed something."   For example, why do the maria, or dark areas, of the Martian plains appear to darken when the polar caps melt?  What causes the mysterious "blue clearing" and the circulation of the Martian clouds?   We still do not clearly understand why the darker features change shape and size erratically as we peer at them from earth.  Spacecraft thus far have provided little additional knowledge of these phenomena, and in many cases have added to the Martian mysteries and our desires to study the planet.   Mars comes into opposition with the earth every 2 years and 50 days on an average, yet each two successive oppositions are unique because the orbit of Mars is considerably more eccentric than that of earth.
    Favorable oppositions of the Red Planet occur approximately every 2 years, either in January or February, or in late summer.  Those that occur in January or February are known as aphelic oppositions (farthest distance for a close approach to earth and sun), and they show Mars as a very small disk of only about 13" arc.  The oppositions that occur in summer, known as perihelic oppositions, bring Mars closer to the earth and sun so that the disk is twice the size as it is in the aphelic oppositions. From the Northern Hemisphere, Mars is seen quite high in the sky during aphelic oppositions and very low in the south during perihelic oppositions.  Consequently, the conditions for observing the planet are improved during the winter months even though the disk is considerably smaller than during the summer oppositions.
    Observations that the amateur astronomer (or should we say more aptly "non-professional astronomer?") can pursue are badly needed for our better understanding of Mars.   Areas of study within a the scope of non-professional equipment should include the following:
    1)  Studies of the Martian polar regions and the two polar caps.
    2)  Long-term programs examining the Martian atmospheric phenomena.
    3)  "Patrol" observations for brightenings on the Martian maria or plains.
    4)  Studies of seasonal changes, including correlations with the melting of the polar caps.
    5)  Visual, photographic and CCD (webcam) studies of surface features.

    Whatever program you undertake, it is better that you do not attempt to accomplish all objectives listed above. Concentrate fully on one or two closely related studies, such as the correlation of the appearance of the polar regions in conjunction with predicted seasonal changes.  There is no substitute for dedicated systematic study of the planet.   Try to overcome the urge to "put too many irons in the fire," and restrict your observations to a well-developed program that you know will lead to success in your studies.  Basic physical knowledge of Mars is summarized in Table 8-1.
    TABLE 8-1. Martian physical data.
    Distance from the sun  = 228 million (km) ave.
    Orbital velocity = 24.1 km sec
    Length of Martian year =  687 earth days
    Equatorial diameter 6800 km
    Maximum size of polar caps = 2200 km
    Mass (x earth) =  0.11
    Albedo = 0.15
    Maximum magnitude =  -2.8
    Maximum apparent diameter =  26"
    Atmospheric constituents mainly N, H2O, CO2, Ar


Figure 1 - A projection map compiled by P. Clay Sherrod, Arkansas Sky Observatory from 378 visual drawings of Mars in the year 1971
    Table 2. The Principal Features of Mars
    The principal features visible on Mars are described below, with their scientific name and Martian longitudes and latitudes given.  Note that because of dust storms and actual morphological changes in the sizes and shapes of nearly all of these features, the given positions are only approximate.  For the latest map from the Mars Section of the Association of Lunar and Planetary Observers (ALPO) click on:
    (in alphabetical order with approximate CENTRAL Martian-centric longitude (listed first) and latitude (both given in degrees)
    Acidallum Mare       30     +45
    Aeolis                   215      - 5
    Aeria                     310    +10
    Aetheria                230    +40
    Aethiopis               230      +1
    Amazonis              140        0
    Amenthes              250     + 5
    Aonius Sinus          105     -45
    Arabia                    330    +20
    Araxes                   115     -25
    Arcadia                   100    +45
    Argyre                      25     -45
    Arnon                     335    +48
    Aurorae Sinus           50    -15
    Ausonia                  250    -40
    Australe  Mare          40    -65
        Baltia                   50    +60
        Boreum Mare        90    +50
        Boreosyrtis         290    +55
    Candor                     90    +10
    Casius                    260    +40
    Cebrenla                 210    +50
    Cecropia                 320    +60
    Ceraunius                 95    +20
    Cerberus                 205   +15
    Chalce                        0    -50
    Chersonesus           260     -50
    Chronium Mare        210     -58
    Chryse                      30   +10
    Chrysokeras            110     -50
    Cimmerium Mare      220    -20
    Claritas                    110    -35
    Copals Palus            280   +55
    Coprates                    65    -15
    Cyclopia                   230    - 5
    Cydonia                       0   +40
        Deltoton Sinus      305    - 4
        Deucallonis Regio  345   -12
        Deuteronilus             0   +35
        Diacria                 180    +50
        Dioscuria              320   +50
        Edom                   345       0
    Electris                    190     -45
    Elysium                   215    +30
    Erldania                   220     -45
    Erythraeum Mare       40     -25
    Eunostos                 220    +22
    Euphrates                335    +20
        Gehon                     0    +15
    Hadriacum Mare       270     -40
    Hellespontica Depress.  340 - 6
    Hellespontus            325     -50
    Hesperia                  240     -20
    Hiddekel                  345    +15
    Hyperboreus Lacus    60    +75
        lapigia                 295     -20
        Iscaria                  30      -40
        Isidis Regio         280     +20
        Ismenius Lacus   330     +40
    Jamuna                     40     +10
    Juventae Fons            63      - 5
        Laestrygon          200         0
        Lemuria               200    +70
        Libya                   270        0
        Lunae Lacus         65     +15
    Margaritifer Sinus       30     - 2
    Memnonia               160      - 2
    Meroe                     285     +35
    Meridiani Sinus         0      - 5
    Moab                      350     +20
    Moeris Lacus           270    + 8
        Nectar                   72    -28
        Neith Regio         275     +35
        Nepenthes          260     +20
        Nereidum Fretum   55     -45
        Niliacus Lacus      30     +30
        Nilokeras              60     +25
        Nilosyrtis             290    +42
        Noachis               330     -45
    Ogygis Regio             65     -45
    Olympia                   200    +80
    Olympus Mons         133    +18
    Ophir                        68      - 8
    Ortygia                       0     +60
    Oxia Pilus                 18     + 8
    Oxus                        10       20
        Panchaia             200     +60
        Pandorae Fretum   340    -25
        Phaethontis          155     -50
        Phison                 320     +20
        Phlegra                190     +30
        Phoenicis Lacus   110     -12
        Phrixi Regio           70     -40
        Promethei Sinus   280     -65
        Propontis               85    +45
        Protei Regio             5     -23
        Protonilus             315    +42
        Pyrrhae Regio         38     -15
    Sabaeus Sinus          340     - 8
    Scandia                   150     +60
    Serpentis Mare          320     -30
    Sinai                          62     -25
    Sirenum Mare           155      -30
    Sithonius Lacus        245     +45
    Solis Lacus                 85     -35
    Styx                         200     +30
    Syria                        100     -20
    Syrtis Major            298      +10
        Tanais                   70     +50
        Tempe                   70     +40
        Thaumasia             75      -30
        Thoth                   256     +30
        Thyle I                 180      -70
        Thyle II                230      -70
        Thymlamata          10     +10
        Tithonius Lacus     85       - 5
        Tractus Albus        80      +30
        Trinacria              268      -25
        Trivium Charontls 198      +20
        Tyrrhenum Mare   255      -20
    Uchronia                  260     +70
    Umbra                     290     +50
    Utopia                     250     +50
        Vulcani Pelagus    15      -35
    Xanthe                      50     +10
        Yaonis Regia       320     -40
    Zephyria                  90       -12

    The telescope required to observe the Martial phenomena depends on the type of program you plan to undertake.  Obviously, if your objective is to patrol the Martian environment photographically, the telescope requirements would be different from those of a telescope used visually to monitor for Martian clouds, using selected color filters.  For serious study of Mars, you should use a least a 4-inch refractor or a 6-inch reflector. The best telescope for an amateur to use to make best use of resolution, light gathering, and-perhaps above all-budget, is a 10-inch Newtonian reflector or popular Schmidt-Cassegrain (SCT) telescope. A 10-inch aperture is just about the size limit that has power capable of resolving the currents of air in our atmosphere.   Anything larger may not be effective on nights of average air steadiness.   Smaller telescopes sometimes can actually be more efficiently used on nights of poor seeing conditions than can larger telescopes.  One prime requisite for your Mars telescope is that it be motor driven and have the capacity for accurate tracking.
    Because Mars shows at best a disk less than half that of Jupiter, highest powers (perhaps 70x per inch of aperture) are necessary for observing its disk. The fine details present on the Martian surface requires your most attentive concentration. The necessity for making constant adjustments to a non tracking, or poorly tracking telescope will eventually frustrate even the most patient observer.
    The disk of Mars is quite small, even when the planet is closest to us, and thus very high magnification is required to view its subtle changes. The optimum magnifications, based on tests with a range of telescopes, all at the same location and operating under the same conditions, are recommended as follows:
    Aperture             Magnification
    6 inch (15cm)          300x
    8 inch (20 cm)         400x
    10 Inch (25 cm)       450x
    12 inch (30 cm)       500x
    14 inch (35 cm)       550x
    16 inch (40 cm)      600x "

    On nights with very poor seeing conditions, observations of scientific quality are impractical if not impossible.  If the steadiness of the air changes rapidly and if there are some moments of average steadiness, magnifications of about half the amounts given above would permit some patrol work.  The efficiency and the reliability of fine detail that are discerned at lower magnifications are not as great as with higher magnifications.
    Use eyepieces of the highest quality, preferably of Orthoscopic or Plossl design, no matter what type of telescope is used. Top quality eyepieces permit the finest color correction, improved eye relief, and the best resolution as opposed to that obtainable by using cheap, inexpensive makes and designs.
    Filters for Observing Mars
    Observation of Mars, more than any other planet, requires good filters. They often make the difference between being able to see some subtle marking and not being able to see it.   A good set of optical glass Wratten (or equivalent) filters is a must for the serious observer, both to cut down unnecessary glare from the Martian disk and to accentuate fine detail.  It is this detail that shows the start of many of the large-scale changes on Mars that are of scientific interest to the amateur.
    Table 8-3 lists the various filters of interest to the amateur astronomer.  Notice that not all filters can be used to any advantage when observing Mars whereas several others can be of considerable help.  Most drawings of Mars should be made using either the orange (No. 21) or the red (No. 25A)
    TABLE 3. Types of glass filters and their uses.
    Wratten Filter Numbers Given
    Number             Color       
             47                   Violet
     Not particularly good for observing Mars; can possibly use for heavy blue clearing.
             80A                Blue 486.5nm
     Use every night to search for blue clearing and to look for high (H2O) clouds in atmosphere.
             58                  Green 538nm
    Use for observations at the "melt line" around polar caps and searching for yellow dust storms.
              12                  Yellow 583nm
    Not much advantage when used for Mars; might accentuate the outline of polar caps and white clouds.
              21                  Orange 593nm
    Very good filter for Mars because it reduces intensity of the reddish coloration and allows observers to note very
    fine delineation on the red plains; in addition it accentuates the maria, showing mottling within them.
           25A                  Red 617.2nm
    Much the same advantages as for No. 21, but with much better color differentiation between red plains and dark maria. Red filters are quite dense and can be used to advantage only with lower powers and steady seeing.

    (nm = nanometers)
    Although the optical glass filters are superior, gelatin sheet filters may be cut and mounted in the standard cardboard frames available for mounting 35-mm color-slide film. Gelatin filters offer only the advantage of being cheaper than the glass. They will wear out and get scratched and stained when fine optical glass will not.  Gelatin filters are usually simply held by hand (requiring the use of an otherwise free hand) between the eyepiece and your eye. Of course, the film should not be touched, because finger-prints are difficult to clean from the soft gelatin material.  Glass filters are normally manufactured by commercial firms to thread directly onto the base of standard eyepieces.  If the eyepiece is not threaded, the glass filter too may be simply held by hand between the eye and the front opening of the eyepiece.
    It is helpful when observing Mars to run through quick overviews with all the filters to check for various features that might be visible through one filter but not through another, making careful notes of each.  However, after you have made these checks (say for the blue clearing), insert either the orange or red filter for critical observations and drawings.  It is best to use the orange filter for photography because the red filter is so dense that a factor of up to 8 times normal is necessary for the proper exposure.
    Auxiliary Equipment for Observing Mars
    Little else is needed for the systematic observation of Mars except a good telescope and steady skies. By using a few auxiliary items, your study of Mars can be greatly expanded. Some are:
    * filar micrometer -
    This device allows you to determine accurately the placement in latitude of Martian features as well as to determine precisely the changes in size of prominent areas (e.g., the diminishing polar cap as the Martian summer approaches).
    The filar micrometer is becoming very difficult to find from commercial sources. The use of each instrument is dependent on the method by which it was made. Most measurements made with such an instrument are made in relation to the total disk size.  For each date the American Ephemeris and Nautical Almanac gives a precise angular size of the Martian disk (in seconds of arc). Measure the Martian feature in proportion to the disk size for that date.  Note also that there are excellent programs available on the Internet today that allow you to download CM calculator programs for any date, time and location of your observing station on earth.  Two such programs are found at: and also at: OnLine Tools from ASO available on this website.  Both provide the precise angular size as seen on each date.
    * observing forms -
    See the Association of Lunar and Planetary Observers (ALPO) Mars Section at: for blank forms in downloadable format....a sample of a completed observing form is found at:
    * accurate time -
    A watch accurate to 1 minute of WWV radio transmission from shortwave radio is necessary OR a direct time sync from: (this example is for central time) can be used to update either your watch or your clock on the PC for daily precision checks.  This aids in the accurate determination of Martian longitudes of various features, and can be used in indirect determination of the east-west extent of a feature.

    * The American Ephemeris and Nautical Almanac -
    ( )
    gives physical data for each date throughout the year, such as longitude of central meridian for 00h 00m Universal Time, phase angle of Mars, size, magnitude, and so on.  Note that for each upcoming apparition, this same data is easily obtained through the Mars section of the ALPO website:   You can also use the outstanding Mars meridian program onto your desktop for instant retrieval of Mars CM longitudes for any given moment by going to the ON LINE TOOLS section of this website.

    Like earth, Mars has two polar caps, although neither is as densely deposited on the Martian poles as on those of earth.  A tilt of up to 24° of Mars as it approaches and recedes from the earth allows you to view one pole well, although the northern cap is easily visible only during the aphelic oppositions. Thus it is somewhat more difficult to study.
    Prior to the Viking spacecraft visits to Mars, it was predicted that the polar caps of Mars were probably composed of frozen carbon dioxide (CO2 ) -or "dry ice" -with traces of water as well.  This hypothesis was first made by astronomers R.B. Leighton and B.C. Murray in 1966, and it was confirmed partially by the 1969 visit to Mars by the Mariner spacecraft.  Beginning with the spectroscope's use in planetary astronomy, scientists have been at odds as to the nature of the caps, whether they were water ice or carbon dioxide ice. As recently as 1952 photoelectric infrared studies by G.P. Kuiper suggested that the caps were composed predominantly of water vapor deposited thinly on the Martian poles, with little or no carbon dioxide being present. By contrast, the Mariner flyby in 1969 revealed a cap composed predominantly of frozen CO2, and having little or no water vapor. More recent trips by the Viking probes, which landed on the surface of Mars in 1976, proved both schools of thought to be correct.
    As Mars recedes from the sun and the Martian autumn and winter approach, the little water vapor present in the atmosphere is slowly deposited at the poles, because the freezing point of H2O is higher than CO2, Then, as Mars rapidly cools below the freezing, or sublimation, point of CO2 (-110°F), the CO2 is also deposited over the thin sheet of water ice. Therefore, neither Kuiper nor the Mariner craft was wrong. If Kuiper's observations were made during the Martian early spring or late autumn, he would have seen an ice cap, composed chiefly of water, from which the CO2 had sublimated because of the higher temperature.  Similarly if the temperature was below -110°F,the Mariner craft may have recorded a cap composed of CO2 that covered any sign of the water ice beneath.
    Observations of the North Polar Cap (
    The northern polar cap of Mars apparently never completely disappears during the aphelic summers.   E.C. Slipher, of the Lowell Observatory, determined that the cap never shrinks below an average width of 6°, usually greater, and may reach a maximum expanse of 72°.  During the advent of autumn on Mars, a haze stemming from the polar regions develops, and any further shrinking of the northern cap ceases. Even during late summer, when one might expect the maximum recession of the cap,  you can sometimes see that it stops shrinking and actually increases in size.  Interestingly, the growth of the cap is always associated with the reappearance of the region.
    The unpredictable nature of this cap can perhaps be explained by the following three factors:
        1)  The topography of the northern polar region may allow for greater deposits of ice or CO2 in the higher altitudes.  Exposure to Martian winds may also increase the effective chill.
        2)  Average temperatures of the polar regions, depending on planet-wide meteorological conditions, may vary during certain seasons, and the distribution of temperature gradients may change from 'Martian year to year.
        3)  The density of the deposits at the caps may also vary in the amount of mass of either the CO2 or H2O vapor.

    Further study of the degree of melting of the northern polar cap are important and desirable, and the effect and cause or the polar haze associated with this cap are equally important.

    Observations of the South Polar Cap )
    During perihelic oppositions of Mars, the large south polar cap is visible to observers on earth. The south polar cap seems to go through more changes than its northern counterpart.  During approaches to Martian summer at perihelic oppositions, the tilt of Mars' axis of rotation can change from 5° to 24°, giving excellent views of the cap. And the closer proximity to the earth during these close approaches helps astronomers make more detailed studies of the southern cap.  Considerable meteorology is associated with the thawing and melting of the southern ice cap on Mars.  It is this defrosting that enables Mars to warm considerably as a result of decreased reflection of sunlight from the large cap. The many cloud formations that are discussed following are the result, either directly or indirectly, of the thawing of this large cap.
    As spring on Mars advances, the southern polar cap appears to split into two segments, the result of rapid thawing of a feature known as Novus Mons, or the "Mountains of Mitchell" (see ).   This large mountain range protrudes high above the cap remnant and is the first visible delineation of the cap seen at each opposition.  Around the edge of the southern cap you might also often see finely detailed rifts that emanate from the melting cap and stretch delicately into the peripheral plains. The meteorological conditions in the Novus Mons area are of particular importance to astronomers.

    Procedures for Observing Martian Polar Caps
    Both the northern and southern polar caps are studied similarly, although each cap has its own characteristics.  At least FOUR areas of detailed studies enable the amateur astronomer to provide important patrol information, as follows:
        1. Polar Meteorology - Examine the caps carefully for such meteorological phenomena as the formation of clouds, mists, or fogs when the polar caps begin to melt and again when they begin to refreeze.  Make examinations for such meteorological phenomena throughout Martian spring and midsummer, and again throughout the autumn when the cap is reforming.  The cloud formation will usually be confined to the hemisphere in which the cap under observation is located.  So, during perihelic oppositions (every 13 years, roughly), the southern cap should instigate meteorological activity in the southern hemisphere.  Likewise, at aphelic opposition, the northern cap will be the precursor of activity in the northern hemisphere.  Predictable meteorological activity that might occur is the formation of the north polar haze during Martian summer and the formation of white clouds in the Hellas basin during July and August when Mars is at perihelic opposition.  Green, yellow, and orange filters aid in the study of such developments.

        2. Melting/Freezing Curves - Draw carefully, or measure on photographs, the size and shape of the polar cap as it begins melting. Continue your drawing and/or measuring until Mars is no longer visible.  Measurements of the polar caps can be made in three ways: (a) by using a filar micrometer,  (b) by using a reticle eyepiece, and (c) direct from a good digital or ccd image while displayed on your computer monitor.   First take a measurement of the size of Mars from north pole to south pole to determine the micrometric extent for any given day. Then convert it into seconds of arc (" arc) by finding the angular extent of Mars on that date from the American Ephemeris and Nautical Almanac (AENA) or via one of the many fine computer Central Meridian and Mars data programs mentioned previously.  Then measure the polar cap width and convert it similarly.   With the advent of good digital and CCD imaging available to the amateur astronomer at a reasonable cost, many contributions have been and continue to be made direct from high resolution images,    
    Measurements can also be attempted (although with a likely considerable reduction in accuracy) via a reticle eyepiece.  By using a graduated reticle inserted into an eyepiece whose field is well known, you can extrapolate those gradations of the reticle in fractions of the field of view. Consequently, by determining the angular extent of Mars' disk on the night of determination (using the AENA or your PC programs), you can compute the division-per-degree ratio of the planet's surface. Then it is a simple matter to determine proportionately the total angular extent of the width of the cap in relation to the pole-to-pole extent (angular size in "arc) of the planet.    
    Such measurements - regardless of which method you are using - enable you to compile a "melting" or "freezing" curve that graphically displays the changes in size of a cap throughout its appearance.  Because the amount of atmospheric activity is thought to be attributable to the degree of melting, the changes in size give you the percentage of the polar cap that is melting or freezing.

        3. Topography - Examine the caps under high magnification during moments of very steady conditions to search for any significant features within the caps, such as Novus Mons in the southern cap. It is important to note the time and date when you first saw the feature, any changes in intensity and character, and the date when you last see it.  You can obtain valuable information concerning the temperature, the terrain of the land, and the relation to atmospheric phenomena from the visibility of features of polar caps.

        4. The "Melt Line" - Measurements and drawings of the polar cap melt line (the perimeter surround each cap) are of interest to the amateur astronomer.  This dark band surrounding the periphery of the polar cap develops as the cap melts in early Martian spring, and it is visible until summer. These bands are probably caused by the melting of the water ice and the dispersion of liquid from that portion of the cap.  Because the amount of H2O that may be locked up in a cap can vary depending on conditions previously described, the melt line also can vary.  Studies comparing the rapidity of polar cap recession and the width of the melt line are
    valuable.  Record the time when you first see the melt line and when it disappears.
    ( )
    Mars is not a static world; it is a planet still alive both geologically and meteorologically.  The atmosphere of this small planet is representative of the climate, the seasons, the chemical constituents of the air and ground, and-of course-the melting of the polar caps. There is no doubt that the seasonal variations in Mars' atmosphere are directly related to the melting and the sublimation of the polar caps as Martian spring progresses.  As the atmosphere condenses at the poles, the formation of clouds and transient veils diminishes, and you can monitor these events readily.  Other than a telescope of moderate aperture, what is most needed for the studies of Martian
    atmospheric phenomena is a good working knowledge of the Martian terrain as it normally appears.  Good maps of the Martian features aid you in quickly identifying transient clouds superimposed over major known areas.
    Five types of atmospheric phenomena are suited for studies by amateur astronomers.  Except for the efforts of these nonprofessional astronomers, very little investigation from earth-based observatories is being made into these phenomena of Martian meteorology, which are:
    (1) whitish blue and white clouds;
    (2) yellow clouds,
    (3) dust storms,
    (4) the blue clearing, and
    (5) the W-shaped clouds.
    Whitish-Blue and White Clouds ( )
    The whitish-blue and the white clouds are attributed to near-surface fogs and mists or perhaps to actual deposits of frost in sheltered depressions on the Martian surface. The very white clouds appear to increase in number and the area they cover at about the time the polar caps melt, and they are not necessarily restricted to one hemisphere. Thus, the white clouds are thought to be seasonal occurrences, beginning in Martian spring and ending in early autumn.  In addition to being seasonal occurrences, it is possible these whitish clouds are daily occurrences as well, forming in early morning on the Martian terminator and disappearing in the heat of day.  It
    is important for amateurs to monitor for such changes to help establish the theory of the possible daily formation of low ground fogs and frost deposits.
    You should record the appearance of any cloud, whether the cloud was visible on the morning terminator or the evening terminator of Mars, or whether it was visible all day.  The areas given in Table 4 are known to exhibit the seasonal forming of white clouds. Most of the reported white clouds are confined to the midtemperate and equatorial latitudes, and they are more predominant in the southern hemisphere than in the northern.  This may be misleading, because the true cause for such distribution may be the favorable circumstances under which we observe the southern hemisphere.  Not only is the planet of greater angular size when its southern hemisphere is visible, but the angle of reflected sunlight from features such as the white clouds is considerably improved over that seen in oppositions of a northern tilt.
    Your observation of the whitish clouds can be considerably improved if you use the Wratten No. 58 green filter for the maria or the Wratten No. 12 yellow filter for the plains.  These filters enhance the brightness of the clouds on the maria and plains.
     (in degrees latitude and longitude, in order of  increasing longitude)
    Feature     Latitude     Longitude
    Aram    0     15
    Sinai    -25     62
    Ophir    -08     68
    Thaumasia    -30     75
    Tharsis     +02     100
    Nix Lux     -08     112
    Olympus Mons     +18     133
    Memnonia     -20     160
    Zephyria     -12     190
    Elysium     +30     215
    Isidis Regio     +20     280
    Neith Regio     +35     275
    Nymphaeum     +08     305
    Hammonis Cornu     -10     315
    Deucalionis Regio     -12     345
    The Yellow Clouds of Mars
    Precursors of the great dust storms of Mars, the yellow clouds form readily during years when Mars is near perihelion and at the time of the Martian summer solstice. Because of the timing of such developments, it is speculated that the yellow clouds as well as the dust storms are raised by the rapid transfer of heat in the thin Martian atmosphere, which causes violent winds during this interval.  The winds carry the clouds of dust and distribute it all across the planet.  Yellow clouds form quite rapidly, and sometimes they spread equally fast.  They can turn the planet into a vague diffuse globe, with no sign of even the brightest or darkest feature beneath the blowing dust.  Although the clouds appear quickly, they can take weeks, even months, to disappear.  It is their longevity that allows amateur and professional astronomers to map the transient circulation patterns of Mars.
    The origin of the dusty yellow clouds is highly localized, coming from the Serpentis-Noachis-Hellas basin area, centered at latitude -28°, longitude 320°. With few exceptions, these clouds, as well as the dust storms, occur quite low in the Martian atmosphere, skirting the landscape of Mars with dust-laden clouds.  You will get best results if you monitor the yellow clouds and the extents of the dust storms using a Wratten No. 12 (yellow), No. 21 (orange), or No. 25 (red) filter.
    The Martian Blue Clearing
    If you view Mars in blue light, you will usually see very little detail. The planet appears to have a uniformly smooth surface with a bright polar cap. The farther you go into the blue region of the spectrum (toward the ultraviolet) in your viewing of Mars, the less you will be able to see. You might glimpse some detail if you use the Wratten No. 80A (medium blue) filter, but all detail vanishes if you use violet light (No. 47 filter). Because of the nature of the materials that make up the Martian landscape and portions of its atmosphere, more light is absorbed in the blue end of the spectrum, whereas most of the light of longer wavelengths - in yellow, orange, and red - is reflected.
    A little-understood phenomenon occasionally occurs during which the Martian surface is very poorly delineated if you use filters of the longer wavelengths that you would normally use in viewing the planet. If you use a blue (No. 80A) or violet (No. 47) filter, however, the surface features again become visible. Such conditions, known as the blue clearing, may last for several days and are of great interest to astronomers.  This clearing in blue light was originally suspected to be caused by a blocking layer of ultraviolet clouds, high in the Martian atmosphere.  Recent studies, however, indicate that this might not be the case, or that another phenomenon-the albedo of various surface features, as well as the polarization of light from those features-might be a partial cause of the blue clearing.
    To search for the blue clearing, merely look first with the blue filter on your telescope and then look without the aid of a blue filter.  It is best. to search for the clearing using the medium blue (No. 80A) filter. If you suspect the presence of the blue clearing move to the more dense No. 47 filter for further scrutiny. You should become suspicious of the presence of the blue clearing if, when viewed through white or unfiltered light, the planet looks like a featureless, orange disk.  Make observations of a blue clearing on every possible date, noting the location (whether the clearing is restricted to a small area or is planet-wide), the date and time you first saw the clearing, and the results of your filter observations.   This unusual phenomenon is not usually restricted to small areas, as are some of the other atmospheric phenomena on Mars; rather, the clearing seems to affect the entire planet on most occasions.
    The Curious W-shaped Clouds
    The most curious of all Martian phenomena-the "W-shaped" clouds-form in the vicinity of massive volcanic peaks. Reported first by Earl Slipher of the Lowell Observatory, and confirmed later as a recurring phenomenon by Charles Capen in 1966, the clouds (usually quite large) apparently are associated with reflections in longer wavelengths of light.  They are therefore best seen in the medium blue to violet range of the spectrum (Wratten No. 80A filter). It is possible that these unusual clouds occur less frequently in the southern hemisphere than in the northern. They are also seen more often in the Martian summer and early fall.  Because the W-shaped clouds move fairly rapidly, it is important that you record them on the date you first see them. Record also their motions across the planet relative to known features; if possible, longitudes on each date should be determined, and the latitudes of these clouds estimated. It is important that you record and report the point of origin of the cloud.
    The W-shaped clouds form near the following features (in order of increasing longitude):
    Feature   near Origin Latitude    Longitude
    Ascraeus Lacus         +110 1040
    Pavonis Lacus         +010 1120
    Arsia Silva                 -090 1200
    Olympus Mons         +180 1330
    It is interesting that all the features listed above are large, volcanic peaks and are located near one another. Perhaps the origin of these clouds is not nearly as simple as might be explained by atmospheric conditions.
    The High, Blue Clouds
    High in the Martian atmosphere are thin clouds not visible to the naked eye, or even to the eye aided by a telescope. Photographs taken in far-violet or ultraviolet light reveal the existence of these small clouds; ultraviolet-sensitive film is often used on steady nights by amateurs who possess large instruments [i.e., 32 cm (12-1/2 inches) and larger] capable of taking long photographic exposures at high magnification.  I emphasize that the would-be Mars observer should become familiar with the Martian surface as it appears without clouds, so that atmospheric phenomena can be recognized for what they are.
    Recording such information can be of great help to the professional planetary astronomer.  It also will enable you, the amateur, to compile all your observations and derive a cloud map of Mars, showing the locations of the most frequent areas of cloud formation and their circulation after being formed.  All clouds and any other atmosphere-related features should be recorded as follows:
    1. The date and time (UT) on a feature is first seen.
    2. The location of the feature relative to known features on the planet.
    3. The approximate size of the feature, in proportion to .the total size of the apparent disk.
    4. The longitude of the feature and an estimate of its latitude.
    5. A disk drawing of the planet, showing the feature (optional).
    6. Date on which the feature is last seen.
    7. The amount and direction of the feature's drift on the planet.


    You can make patrol observations of the Martian surface either telescopically or photographically, but you should make them as consistently as possible. Basically, by setting up a patrol, you scan the surface on every available date so that you are sure to see any rapid changes. Report such changes immediately so that others may study them. Such changes include cloud formation, blue clearing, dust storms, changes in the size and shape of the maria, the appearance of bright spots on the plains or maria, new features in the polar regions, and so forth.  Unless some new phenomenon is noted, you need not make drawings unless you have the time and the desire to do so.
    Seasonal  changes....the Maria:  Because Mars has an axial tilt of 24.9 degrees, it has a seasonal cycle, much like that of earth....except not to the predictable levels of our planet.  On Mars the seasons are much more extreme and last twice as long.  Some of the effects of seasonal changes have been discussed via the polar  caps and these basic changes cause most of the other seasonal changes on Mars.  For example, the density of the atmosphere increases proportionately with the melting of the polar caps. The density increases as the caps melt and sublimate, and it decreases as they refreeze in Martian autumn and winter. With the melting of the ice caps, the amount of sunlight reflected from the planet decreases, which causes more heat absorption by the planet's surface.   This in turn, results in increased atmospheric convection.    
    From your standpoint as an amateur observer, the most notable seasonal changes, other than those of the caps themselves, occur in the maria, which are seen as dark regions.  The changes were formerly thought to be caused by growing vegetation that made these regions darken as the Martian summer progressed lighten as autumn approached.   We now know that these are related to the albedo, or the amount of sun- light absorbed compared to the amount reflected. The more light that is reflected, the brighter the feature appears to us.
    The wave of darkening  as it has been termed, begins in midspring on Mars and continues until most of the polar ice cap is gone. It is more predominant in perihelic oppositions than in aphelic ones, possibly as a result of the differing densities of the north and south caps. As the caps melt or sublimate, the darkening progresses from pole to equator. An increase in atmospheric H2O slowly disseminating from the pole and drifting toward the equator could possibly explain such sequential darkening.  Not only do the features darken, their size also often increases greatly over their size in the early spring, and they even change their shape and their position on the planet.  Again, your familiarity with the normal appearance of the maria is essential.  Only when you know how they are supposed to appear, can you detect the subtle seasonal changes that always occur.  Table 5 is only a small sampling of areas that exhibit changes such as those described.    
    You can determine the relative degree of darkening of the maria by using a scale of 1 to 10, noting the relative contrast between a feature and its surroundings, with 1 being the lowest contrast and 10 the highest contrast.  All the maria can be better differentiated by using color filters; the orange (Wratten No. 21) or the red (No. 25) are the best for such studies.
    TABLE 5. Notable areas of seasonal changes
    Feature                    Latitude                     Longitude
    Margaritifer Sinus     -02     30
    Hydrae Sinus     -02    30
    Mare Australe     -65     40
    Acidalius Fons/Tempe     +58    60
    Nilokeras/Lunae Lacus     +25     60
    Solis Lacus    -35     85
    Candor/Tharsis    +10     90
    Aonius Sinus    -45     105
    Amenthes    +05     250
    Thoana Palus     +35     256
    Thoth     +3     256
    Nepenthes     +20     260
    Moeris Lacus     +08     270
    Antigones Fons/Astaboras     +22     290 .
    Syrtis Major     +10    298
    Aeria     +10     310
    (in order of increasing longitude)

Figure 2.  Drawing of Mars made by the author, Feb. 25, 1980.  The prominent feature, Syrtis Major, is seen near the central meridian (see following);
north polar cap is at the bottom, as it should be in all correctly oriented astronomical views.
    To compile a history of the appearance of Mars is a rewarding experience. You can compile the history by drawing on a standard disk form the appearance of Mars as you see it in the telescope, or you can photograph or record via CCD the planet. Whichever way is chosen, adhere to it.  Do not switch back and forth to one or the other method.  Photographic records of the planets, particularly Mars, can actually be  less desirable than high-resolution drawings.  With the aid of your 10- to 12-inch (25- to 30-cm) telescope, you can detect nearly as much as can professional astronomers making photographs through the largest telescopes on earth.  However, the great advantage of a photographic program is that the photo verifies itself, so to speak.  Modern webcam-type astro cameras are ideally suited for incredibly high resolution results of stacked images.
    A photograph of a W-shaped cloud would be of great value, for example, and would virtually substantiate itself even if observers elsewhere had not seen this transient feature.  For photographing Mars via film photography, choose a high- contrast, fine-grain, and red-sensitive film. The Kodak 2415 film, developed in Kodak HC-110 developer, dilution D, is best suited for photography of the red planet in black and white format.  For CCD imaging, very high resolution, small field CCD chips are desired.  Remarkably clear and quick results can be obtained via modern digital cameras which can be operated in manual mode.
    Visual Studies of Mars
    Visual studies of Mars are better suited for the endeavors of the amateur astronomer than are photographic studies, unless on is equipped with high resolution CCD equipment.   Telescopic studies reveal low contrasts and subtle detail that cannot be recorded by the camera. You can record all the Martian phenomena thus far discussed quite accurately by making highly detailed drawings on which you draw and label precisely what you see in the eyepiece. During moments of steady seeing, you will be able to see extraordinary detail crisscrossing the Martian surface.  Your first efforts at drawing the tiny disk of Mars may seem somewhat comical, with strange abstract figures and geometrical patterns drawn on a white circle. With a little practice and the experience of only a few drawings behind you, however, the very low contrasts and subtle details begin to form, appearing much as they do in the map shown in Figure 1.  Both Mars and earth have atmospheres, and it is only when both atmospheres are simultaneously steady that the telescope can penetrate to the Martian surface to view the fine network of detail.
    The trained Mars observer knows to wait for such moments.  Drawings of the Martian disk provide a permanent record of your impression of the planet.  No drawing is without a certain amount of bias, showing features that result from some preconceived notion of what you think "should" be there.  Draw only what you really see - not what you think you "should" see.   If you are not familiar with the Martian features, particularly the very small ones, you might not record some fine linear marking that you saw only for a moment, simply because you do not trust what your eyes have actually seen.
    When seeing conditions permit, attempt to make observations at least every other night, preferably at about the same time each night.  Ideally, make two drawings each night, when possible, to allow for greater coverage of Martian longitude.  These drawings can make a composite record of all changes seen over a long period as well as show the expansion of very large features.  If you make a second drawing 4 hours after the first, almost 600 change in longitude on Mars will be shown as a result of the rotation of the planet.  Use a standard form, part of which is a circle 2 to 3 inches in diameter, as a standard for making visual observations of Mars. The form should
    have places where additional data can also be recorded, including the following:
    1. The observer's name, the date, and time of the observation.
    2. Telescope used, magnification, and any filters used.
    3. The steadiness of the air on a scale of 1 to 5 (5 best, 1 worst).
    4. Transparency of the sky (1 to 6, representing the magnitude of the faintest star seen to the naked eye).
    5. Any transient or unusual features on the planet.
    6. Martian longitude on the central meridian at the beginning of the drawing.
    Make copies of each drawing as accurately as possible from the original, retaining the original and filing it in some systematic way.  Send the copies to: MARS SECTION of
    The Association of Lunar and Planetary Observers
    or e-mailed direct to: This email address is being protected from spambots. You need JavaScript enabled to view it. provides the link to the standard observing form used by the Mars section of the Association of Lunar and Planetary Observers (ALPO).  Also, we have an excellent form in PDF format made by Carlos Hernandez and graciously provided to ASO for use by anyone by going to the ASO OnLine Tools section.
    For your drawings, it is best to follow a strict sequence in which features are recorded to provide accuracy and consistency in your records.  The following sequence is recommended:
    1. Draw the polar caps first. This allows for better accuracy in the placement of other features, and sets up a basic north-south orientation for you.
    2. Draw all prominent detail in the center of the disk, using the maria as guides for small, indistinct detail.
    3. Draw details on the preceding limb (eastern, or left on the form shown reference above).  Notice that south is at the top on this form, as it should be in all drawings.
    4. Sketch in all fine details, looking carefully for clouds, "canals," bright spots, and so on.
    5. Add details seen in filters that were not seen without them, but be sure to note (by a small number) which were seen this way, and through what filter.
    Adhering to this routine helps you to place features in their proper positions, rather than too far north, south, east, or west. After all the most prominent details have been drawn in their approximate positions, then draw the finer details on the drawing in relation to the obvious features.  A normal Mars drawing should require a full hour.  You can take the time to wait for moments of optimum steadiness in order to discern the finest detail.

    To make your observations more scientifically valuable, it is necessary that you determine the central meridian of the Martian globe at the time of any particular observation.  For each drawing made, or photograph taken, determine the longitude of the central meridian. The central meridian (CM) is merely an imaginary line passing from the north pole to the south pole of the planet, perpendicular to the equator.  Record the central meridian at the time when the drawing was begun, and again when the drawing was finished.    
    An excellent downloadable computer program will assist you in determining exact longitude for any time, date or earth location; go to the Meridian  program in the ASO Tools Section for instant longitude readings for the red planet.

   NOTE:  If it took you one hour to render the disk drawing, then 14.6 degrees of longitude will have rotated past the CM. For a photograph, the CM recorded should be that at the instant the drawing or photograph was made.

     MARS FIG3
    FIGURE 3. Drawing showing the central meridian

    Because the rotational rates of Mars and the earth are almost the same, the same face of Mars will be visible with only slight deviation for several successive nights. Over a period of 36 days, you can view an entire rotation of Mars through 3600 of longitude if you make your observations each night at approximately the same time.
    Another important advantage in determining Martian longitude is that it allows you to determine the correct longitudinal placement of features, as well as their angular size horizontally.  The longitudes of Mars' surface features are determined by noting the time, to the nearest minute, at which that feature is exactly centered on the Martian disk (the central meridian would then cut symmetrically through the feature).  To determine angular longitudinal expanse, one simply times the instant the preceding edge of the feature first crosses the CM, and the instant the following edge crosses some moments later.
    After determining the longitudes for each timing, the difference of the two is the angular extent in longitude of that feature.  The process of determining longitudinal placement of features on Mars is much easier than for those on Jupiter or Saturn, because of the much slower rate of rotation of Mars.  Closer precision may be achieved if a vertical wire in a finely threaded cross-hair eyepiece is positioned to exactly coincide with a north-south line.
    An even more accurate determination of both latitude and longitude of any Martian feature will be afforded through direct measurements from quality high resolution CCD or photographic images.
    Reducing the Timings To Determine the Longitude
    Every planet has 360° of longitude starting with 0° and progressing all the way through 359.9°.  On Mars the 0° point -the starting point for all subsequent measures- was arbitrarily set at the center of a prominent feature, Sinus Meridiani, which is also located near the Martian equator (-05°). All subsequent markings are measured in increasing longitude westward from that point, as they are on earth, as we measure westward and eastward from the 0 degree longitude of Greenwich, England.  The use of either an on-line Mars ephemeris database to determine longitude (and thus exactly what features you might be viewing, or interesting new clouds or developments over existing features) or the AENA will result in much greater scientific value to your observations.
    It has been said that Mars may well hold the key to the development and evolution....and perhaps even the HISTORY.... of our solar system and our planet earth.  Perhaps Percival Lowell was not so wrong after all about his hypotheses regarding Mars....maybe at one time there was enough water to sustain life of some type, and we know that Mars is a drying and dying world.  Perhaps Mr. Lowell was merely speculating a bit too late in the prehistoric history of a primitive world of mystery.
    Often I wonder what EARTH might appear to be if all life suddenly ceased upon its more skyscrapers, no bridges nor city dumps or great dams upon the waterways.  If our planet were left alone - void of the force that we call "biology" - for perhaps three million years, what signs would be visible upon this planet to the visitors from some world only 36 million miles away?  The greater forces of geology, meteorology, and the force of sunlight itself may well render our world to appear "drying and dying" to those yet to come.
    Dr. Clay
    May not be published, reproduced or transmitted in part nor whole without prior permission in writing
    Copyright, P. Clay Sherrod, November 2015
    Arkansas Sky Observatory

Copyright Arkansas Sky Observatory © 2016  [A.S.O.] All rights reserved. Revised:

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