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 carbon dioxide (CO 2 ) and underlying water ice (H 2 O), 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. Mars offers both casual and serious observers many challenges and delights, as well as providing astronomers a laboratory to study the atmosphere and surface of another planet. Some Martian features even appear to shift position around the surface over extended periods of time. Because Mars has no oceans its charted land area is about equal to that of our own planet because Mars has no oceans.
The orbits of Earth and Mars are elliptical, Mars having a highly eccentric orbit while that of Earth is more nearly circular. The distance between the Earth and Mars varies from 248,700,000 miles, when Mars is in conjunction with the Sun and may approach within 34,650,000 miles during Perihelic apparitions, or as far away as 63,000,000 miles during Aphelic apparitions. A brief description of planetary motions in orbit around the Sun can be found in Planetary Aspects.
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. It will not be safe to observe Mars until it is at least 12 degrees away from the glare of the Sun. From the time we first see Mars rising early in the morning sky until western quadrature (90° west of Earth) and the phase or terminator will be increase. After quadrature the phase will decrease until it nearly disappears around opposition. For detailed definitions and graphics for the motion of Mars in our sky see this excellent web site: 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.
Tables presented in the pre-apparition reports are based on computer programs written and compiled by the author using equations found in the book Astronomical Algorithms by Jean Meeus [ Meeus, 1991]. The location of features on Mars that are referred to in this general articles can be found on the ALPO Mars Section Mars Chart and the Ebasawa Mars Chart.
DAYS AND SEASONS ON MARS
The Martian solar day, or "sol", is about 40 minutes longer than a day on Earth. Consequently Mars only rotates through 350° of longitude in 24 hours. As a result, astronomers on Earth observing a particular Martian surface feature one night, will see that same feature positioned 10° further west on Mars (or closer to its morning limb) the next night at the same civil time.
Mars and Earth have four comparable seasons because their axes of rotation (obliquity relative to orbital plane) are both tilted at about the same angle to their respective orbital planes, 25.1894°+/-0.0001° for Mars and 23.5° for Earth [ Kieffer et al , 1992] [ Yoder and Standish , 1997]. NOTE: Prior to Marinier 9 this value was 25° +/- 0.1° [ Michaux, 1972]. In describing Martian seasons, scientists use the term "Ls" which stands for the Areocentric longitude of the Sun along Mars’ ecliptic. The zero point, 0° Ls, is set at the Martian vernal equinox when the Sun, moving northward, appears to cross the celestial equator in Mars’ sky. Thus, 90° Ls is the northern hemisphere summer solstice, 180° the autumnal equinox, etc. The seasons are, of course, reversed for the southern hemisphere.
Figure 2. Graphs showing the relative positions of Earth and Mars in their respective orbits around the Sun. Left: show the seasons for each planet. Right: Shows the relative posits of each planet as it relates to cardinal points in each orbit.
The Martian year is 1.88 tropical Earth years consisting of 668.59 Martian days (sols) or 686.98 Earthy days and its mean synodic period 779.94 mean days. We find the synodic period from the mathematical expression:
1/s = 1/Pe - 1/Pm, where Pe = 365.26 days and Pm = 686.98 days.
The axis of Mars does not point
toward Polaris, our North Star, but is displaced about 40°
towards Alpha Cygni. Because of this celestial displacement,
the Martian seasons are 85° out of phase with respect to
terrestrial seasons, or about one season earlier than ours.
Consequently, when you observe Mars next spring and summer, it
will be winter and spring, respectively, in the Martian
Note: Days = Terrestrial days, Sols = Martian days, and Ls = Areocentric longitude of the Sun.
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 92955807.267 miles or 149,597,870.691 km.
MAKING OBSERVATIONS OF MARS
The diameter of Mars is about 53% that of Earth, and its mass is only 10% that of the Earth’s. Mars has a polar diameter of 4,195.7 miles (6,752.4 km) and an equatorial diameter of 4,220.6 miles (6,792.4 km) [ USGS , 2005]. Mars’s surface gravity is 38% of Earth’s. So, the apparent size of Mars, as viewed through a telescope from Earth, will vary from as small as 13.8 seconds of arc during Aphelic apparitions, and as large as 26.04 seconds of arc during Perihelic apparitions in the year 25,695 A.D.
It is very important that each visual or photographic observation (including CCD images) be accompanied by a written data record made at the time of observation and/or imaging and not left to memory the following day. Whether or not the observations include visual drawings, it is recommended that the following data be recorded:
Anyone who observes Mars will find it rewarding to make a sketch of whatever is seen, both to create a permanent record and to help train the eye in detecting elusive detail. Start with a circle 1.75-inch (42 mm) in diameter. Draw the phase defect, if any, and the bright polar caps or cloud hoods. Next, shade in the largest dark markings, being careful to place them as accurately on the disk as possible. At this stage, record the time to the nearest minute. Now add the finer details, viewing through various color filters, starting at the planet’s sunset limb. Finally, note the date, observer’s name, the instrument(s) used, and any other relevant information.
Modern technology, like CCD and digital cameras, has greatly increased the efficiency even of small telescopes that in the past were considered less than optimal for serious planetary observing. In addition, image processing can often compensate for such factors as low contrast, poor color balance and even sharpness. Another plus is that because CCD and digital cameras can capture images much faster than conventional photography, atmospheric turbulence is less likely to spoil the results. It is important that serious imagers of Mars carefully calibrate their images by doing bias, flat fields, and dark frames. This way the images become quantitatively accurate for analysis and they will be much easier to process.
Recently many amateurs have been using webcams for imaging the planets. These inexpensive little devices do require a computer but are relatively easy to use and, with inexpensive (or even free!) software they can produce striking images of Mars. It is suggested that amateurs wishing to image Mars for the first time try using a web cam.
It is highly recommended that all astronomers, whether photographers, CCD or digital camera imagers, or visual observers, use at least a basic set of tricolor filters according to the following guide:
Those who use CCD cameras often employ filters designed for the spectral response of their cameras. If this is the case, it is necessary to provide information about what filters were used, so that those who receive the images will know the wavelengths involved. It is also suggested that, when using infrared or ultraviolet filters, the spectral range or the "bandwidth half-maximum" (BWHM) be provided. This information is usually readily available from the filter manufacturer.
The Mars observer will make his observations and studies more profitable if he familiarizes himself with a few other physical parameters:
De or Sub-Earth Point. The axial tilt of Mars relative to Earth is defined by the declination of the planet Earth (De) as seen from Mars. De is also equal to the areographic latitude of the center of the Martian disk, which is known as the sub-earth point. ("Areo-" is a prefix often employed when referring to Mars or "Ares.") The latitude is (+) if the north pole is tilted toward Earth and (-) if the south pole is tilted toward Earth. This quantity is an important factor when drawing Mars or when trying to identify certain features.
Ds or Sub-Solar Point. The axial tilt of Mars relative to the Sun is defined by the declination of the Sun (Ds) as seen from Mars. The Sub-Solar Point (Ds) is (+) if the north pole is tilted toward the Sun and (-) if the south pole is tilted toward the Sun. This quantity is an important factor when drawing the phase terminators of Mars or when the polar caps may or may not be in Sunlight.
The Martian Central Meridian (CM), an imaginary line passing through the planetary poles of rotation and bisecting the planetary disk, is used to define the areographic longitudes on the disk during an observing session. It is independent of any phase that may be present; if Mars presents a gibbous phase, then the CM will appear to be off center. The CM is the areographic longitude in degrees, as seen from Earth at a given Universal Time (U.T.). It can be calculated by adding 0.24°/min., or 14.6°/hr., to the daily CM value for 0h U.T. as listed in The Astronomical Almanac).
The terminator (phase defect) is the line where daylight ends and night begins The phase , or defect of illumination, is given in seconds of subtended arc on the apparent disk, or in degrees (i), or the ratio (k), to define how much of the Earth-turned Martian disk is in darkness. The sunset terminator appears on the eastern side, or evening limb, before opposition; after opposition, the terminator becomes the sunrise line on the western side, or morning limb. At opposition, there is no perceptible phase defect (See Figures 3 & 4).
Figure 3. The orientation and nomenclature of the Martian globe as seen from Earth through an astronomical telescope. The figures indicate a simple inverted view of the disk of Mars; where south is at the top, bottom is north, the right side is terrestrial east or the Martian west (morning limb), and the left side is terrestrial west or Martian east (evening limb). Mars appears to rotate from Martian west to east, or right to left.
Figure 4. The orientation and nomenclature of the Martian globe as seen from Earth through an astronomical telescope. The figure indicates a simple inverted view of the disk of Mars; where south is at the top, bottom is north, the right side is terrestrial east or the Martian west (morning limb), and the left side is terrestrial west or Martian east (evening limb). Mars appears to rotate from Martian west to east, or left to right.
SURFACE FEATURES OF MARS
The dark Martian surface markings, called "maria" or "albedo features," were once thought by some astronomers to be great lakes, oceans, or vegetation, but space probes in the 1970’s revealed them to be vast expanses of rock and dust. Windstorms sometimes move the dust, resulting in both seasonal and long-term changes in these markings. These 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, C.F. Capen showed that the wave of darkening is in actuality a "wave of brightening" [ Michaux, 1972, Capen, 1976, Dobbins, 1988]. 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. Light and dark surface features tend to change in albedo and color contrast diurnally and more slowly as the seasons change. Seasonal variations are usually predictable, but secular or long-period changes are unpredictable.
Seasonal Changes. Several regions that display seasonal changes are:
Syrtis Major is the planet’s most prominent dark area. Classical observations indicated seasonal variations in the breadth of this feature: maximum width occurring in northern mid summer (145° Ls), when its eastern edge expands eastward to about 275° W. longitude [ Dollfus, 1961]. Minimum width classically occurs during early northern winter, just after perihelion (290° Ls) [ Antoniadi, 1930, Capen, 1976]. However, recent observations by A.L.P.O. astronomers and the Hubble Space Telescope (HST) suggest that no such variations have occurred since 1990 [ Lee, et al., 1995.].
The Syrtis Major area has also undergone some rather dramatic long-term, or "secular," changes over the years. During recent apparitions it has become narrower and more blunted in appearance compared to the 1950’s. After the 2001 dust storm this feature appeared thinner and more tapered to the north than it was before the storm [ McKim, 2002]. Osiridis Promontorium became very dark in 1984, appearing as a dark bar jutting out into Libya from the northeast border of Syrtis Major. This feature was conspicuous in 1879, 1909, and during the 1940’s and 1950’s. The broad "canal," Nilosyrtis that curves northeast from the northern tip of Syrtis Major, was inconspicuous in 1984 [ Parker et al., 1999].
The Nepenthes-Thoth (268° W, 08° N) feature, lying to the west of the Elysium shield, so prominent in the 1940’s, and 1950’s, decreased in size in 1960 and began fading in 1971. It was virtually undetectable in 1984. Nodus Laocoontis (246°W, 25°N), first described by S. Kibe in 1935, had faded during the 1970’s and was not seen during the 1983-1985 apparition.
Hellas. One of the most active areas on Mars is the Hellas Basin (292° W, 50° S), not only because of its dynamic meteorology but also for its never-ceasing albedo changes. Surface structure becomes apparent in this area when its darker center (Zea Lacus) seems to extend its arms or canals (Alpheus) to the north, and connect Mare Hadriacum (265° W, 40° S) and Yaonis Fretum (318° W, 43° S) eastward to the western edge of Peneus. As the Martian southern summer solstice approaches, the basin often becomes flooded with dust if a violent storm begins. Hellas was the initial site of the great planet-encircling dust storm of 2001 and is a region that bears careful scrutiny during the 2003 apparition, since Mars will then be in its "dusty season."
Hellas was also was involved in both the December 11, 1983, the January 5, 1984, dust storms [ Beish et al., 1984]. As these apparitions progressed and southern hemisphere winter got underway, Hellas and the high basin Argyre (30°W, 50°S) appeared brilliant white on the southern limb. Both of these great basins are the water-ice reservoirs of the southern hemisphere and are often covered with frost or with low clouds. These features were often confused with the South Polar Cap (SPC) or its winter hood, owing to their foreshortened appearance due to the planet’s axial tilt.
Solis Lacus is called the "Eye of Mars" because, with the surrounding light area called Thaumasia, it resembles the pupil of an eye. Centered at 90° W, 30° S, Solis Lacus is notorious for its variability. Small and relatively inconspicuous in 1971, it underwent a major dark secular change in 1973, perhaps as a result of the major dust storms occurring during those years [ Dobbins et al., 1988]. During the ensuing two decades it remained large dark oval with a north-south orientation [ McKim, 1992]. During the 1992-1993 apparition Solis Lacus presented as a small, dark oval, but it enlarged and elongated in 1975 and has remained a large dark oval feature oriented slightly east-west until late 2001. At that time, after the massive dust storm had subsided, it appeared smaller than it had before the storm and the "canal" Nectar had all but disappeared [ McKim, 2002].
Just west of Solis Lacus other areas have undergone changes are Daedalia-Claritas and Mare Sirenum. In 1973, the normally light region located between Sirenum M. and Solis Lacus, Daedalia-Claritas, underwent a dramatic darkening, which persisted through 1980. In 1984, this region had returned to its normal light intensity. However, during March and April 1984, A.L.P.O. observers reported that northeastern M. Sirenum had weakened considerably, possibly as a result of dust deposition from the storms sighted earlier in that region [ Capen, 1986].
Early in 2001, after the dust had cleared from the 2001 storm, IMP observers reported a significant darkening in Daedalia-Claritas that extended eastward into Thaumasia near the site of the Phasis "canal." Both this region and nearby Solis Lacus bear careful watching in 2007.
Trivium-Cerberus (210° W, 22° N), lying on the southern rim of the Elysium shield, is another feature of great interest to professional Mars researchers. During the 1950s it was a classically dark feature 808 x 249 miles (1,300 x 400 km) in size, but it weakened somewhat in the 1960s. During the 1970s it varied in size and intensity from prominent to near invisibility. This area appears to have been covered over with dust during February and March of 1982 [ Parker et al., 1990]. A generally "washed out" appearance was reported during the remainder of that apparition and very low contrast has been observed ever since. Dust storms during 1983 and 1984 appeared to further lower the contrast of the Elysium and Trivium Charontis region [ Parker et al., 1999]. On May 14, 1984,A.L.P.O. observers reported that the Trivium Charontis--Cerberus was very difficult to see or missing from the face of Mars [Beish, 1984 and Troiani, 1996]. Except for a brief darkening in 1995 it has remained nearly invisible, appearing as two or three dots on a half-tone background [ Moersch et al., 1998. Troiani et al., 1998].
In 1977 A.L.P.O. Mars observers reported a new dark area on the western side of the Elysium shield volcanoes [ Capen and Parker, 1980] Astronomers reported that the normally insignificant "canal" Hyblaeus (240°W, 30°N) had darkened and expanded westward into Aetheria. Termed the "Hyblaeus Extension" by Capen, this change has persisted to the present. Interestingly, it was subsequently found on Viking Orbiter photographs taken in 1975, apparently undetected by Viking scientists. This is an example of the importance of ground-based observations of Solar System objects. On June 10, 1984 (162° Ls), A.L.P.O. observers photographed a further darkening in this region, located in Morpheos Lacus (228°W, 37°N). This darkening persisted into the 1980’s & 1990’s along with other changes near Elysium, notably the lightening of the wedge-shaped feature, Trivium Charontis. The entire region near the huge Elysium volcanoes appears to be in a state of flux and should be monitored often.
Cerberus III. A recent surface change is the appearance of a very conspicuous dark band across Hesperia. This has been named for the faint "canal" Cerberus III and was first detected in 1986 [ Beish et al., 1989].
In 1990 A.L.P.O. observers reported a bright streak running east-west from 160°W to 260°W at 50-60°N. At 220°W longitude, another streak extended at right angles from it and extended southward into Elysium. These streaks, also observed in 1995 and 1997, appeared bright through all filters, and their nature is not known. This entire region bears careful scrutiny and will be well placed for observation during the Perihelic apparitions of the early 21st Century.
The Polar Regions - The brilliant white polar caps of Mars are among the planet’s most prominent and intriguing features. Because the Martian polar caps are affected by the planet’s 25.2° axial tilt, they are observed to thaw and re-accumulate in an annual seasonal cycle. Indeed, many of the observed surface changes and atmospheric phenomena appear to be directly coupled to the seasonal climate which causes the spring thawing phase of one polar cap as autumn allows the reformation phase of the opposite cap.
Planetary scientists have shown the white substance of the Martian polar caps is probably some form of crystallized water (H 2 O) or solidified volcanic carbon dioxide (CO 2 ). Space mission data sent back from Mars confirmed Earth-based observations of frozen water and carbon dioxide in the Martian polar caps. Sublimation of the H 2 O and CO 2 contributes to the Martian atmospheric clouds and hazes as the spring and summer cap-thaw becomes more rapid.
Many interesting cloud or ice-fog formations appear at the polar regions of Mars during late spring as the sub-solar point rises higher in the Martian latitudes. Since the atmospheric pressure is usually below the point that water can become liquid and temperatures are usually below the freezing point, especially in the polar regions, melting of the polar ice is not possible. The sublimation process is responsible for the water vapors we find in the Martian atmosphere that forms hazes and clouds. Both polar regions exhibit similar behavior during their respective early-spring periods. Often, each emerges from its winter darkness when its dull-gray hood begins to dissipate as spring progresses, then its brilliant polar cap peeks out and begins to retreat pole-ward.
Clouds and Hazes - 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. The A.L.P.O. Mars Section, using visual data and photographs from professionals and amateurs around the world, has conducted an intensive study of Martian meteorology. The first report, published in 1990, analyzed 9,650 IMP observations submitted over eight Martian apparitions between 1969 and 1984 [ Beish and Parker, 1990]. This study has now been expanded to include 24,130 observations made between 1965 and 1995 [ Beish, 1999]. Statistical analysis indicates that discrete, water ice crystal cloud activity and surface fog occurrences are significantly higher in the spring and summer of the Martian northern hemisphere than they are during the corresponding seasons in the southern hemisphere.
To participate in this important study, it is essential that A.L.P.O. astronomers employ blue (W-38A or W-80A) and violet (W-47) filters when making visual, photographic, CCD or digital camera observations of Martian clouds and other atmospheric phenomena.
Discrete clouds have been observed on Mars for over a century. In 1907, a remarkable, recurring W-shaped cloud formation was observed each late-spring afternoon in the Tharsis-Amazonis region [ Slipher, 1962]. A decade later, C.F. Capen proposed that the W-clouds are orographic (mountain-generated), caused by the up-lifting of water vapor-laden atmosphere. [ Capen, 1984 and Capen, 1986]. In 1971, the Mariner 9 spacecraft probe confirmed these observations, and showed that they were water clouds near the large volcanoes Olympus Mons (133° W, 18° N), Ascraeus Mons (104° W, 11° N), Pavonis Mons (112° W, 0° N), and Arsia Mons (120° W, 9° S). Although often observed without filters, these clouds are best seen in blue or violet light when they are high in the Martian atmosphere and in yellow or green light when they are at very low altitudes. Similar orographic clouds are also frequently observed over the Elysium Shield region.
In addition to such dramatic orographic clouds, Mars exhibits many localized, discrete clouds. These rotate with the planet and are most often seen in northern spring-summer over Libya, Chryse, and Hellas. One remarkable example of such a discrete topographic cloud is the "Syrtis Blue Cloud", which circulates around the Libya basin and across Syrtis Major, changing the color of this dark albedo feature to an intense blue. Originally named the "Blue Scorpion" by Fr. Angelo Secchi in 1858, this cloud usually makes its appearance during the late spring and early summer of Mars’ northern hemisphere. It was prominent during the 1995 and 1997 apparitions and is best seen when the Syrtis is near the limb. Viewing this cloud through a yellow filter causes the Syrtis to appear a vivid green (yellow + blue = green).
Limb brightening ("limb arcs") are caused by scattered light from dust and dry ice particles high in the Martian atmosphere. They should be present on both limbs, often throughout the apparition, and are also best seen in blue-green, blue or violet light. When dust is present, these arcs are often conspicuous in orange light.
Morning clouds are bright, isolated patches of surface fog or frost near the morning limb. The fogs usually dissipate by mid-morning, while the frosts may persist most of the Martian day, depending on the season. These bright features are best viewed with blue-green, blue, or violet filters. Occasionally, very low morning clouds can also be seen in green or yellow light.
Evening clouds have the same appearance as morning clouds but are usually larger and more numerous than the latter. They appear as isolated bright patches over light desert regions in the late Martian afternoon and grow in size as they rotate into the late evening. They are best seen in blue or violet light.
The size and frequency of limb clouds appear to be related to the regression of the northern, rather than the southern, polar cap. Both limb arcs and limb clouds are prominent after aphelion (70° Ls), but limb clouds tend to decrease rapidly in frequency after early summer, while limb hazes become more numerous and conspicuous throughout the northern summer.
Equatorial Cloud Bands (ECB) appear as broad, diffuse hazy bands along the Martian equatorial zone and are difficult to observe with ground-based telescopes. CCD images and the HST have revealed that these clouds may be more common than suspected in the past. Their prevalence during the 1997 apparition led some conferees at the Mars Telescopic Observations Workshop-II (MTO-II) to postulate that many limb clouds are simply the limb portions of ECBs. A.L.P.O. astronomers are encouraged to watch for these elusive features during the 2010 apparition. Are they really more common, or could it be that our improved technologies merely allow us to detect them more easily?
ECBs are best observed visually through a deep-blue (W47 and W47B) Wratten filters and may be photographed or imaged in blue or ultraviolet light.
New technologies, such as CCD cameras, sophisticated computer hardware and software, and large-aperture planetary telescopes have resulted in a virtual explosion in advancing the study of our Solar System. Never before, for example, have we been able to readily detect the delicate wispy Equatorial Cloud Bands on Mars as well as we can now with CCD imaging.
Dust storms. Recent surveys, including our Martian meteorology study, have shown that dust events can occur during virtually any season [ Martin and Zurek , 1993; Beish and Parker , 1990]. Martin and Zurek found the main peak occurs during the southern Martian summer on or about 285° Ls, just after southern summer solstice, but a secondary peak has also been observed in early northern summer, around 105° Ls.
The ALPO Mars Section’s statistical analysis indicates that the number of dust clouds is more often observed from mid-southern summer, between 241° and 270° Ls, with a peak period at 255° Ls. This is substantiated by Viking space mission science studies on dust clouds indicating that most dust cloud activity occurs during southern spring and summer [ Wells , 1979]. In the past, many of the major dust events occurred during the same seasonal period and led some researchers to refer to these major dust storms as "precursor storms prior to planet-encircling events." When a major dust event does occur during this period then we find that the highest probability of predicting planet-encircling dust storms occurs during mid-southern summer at or near 315° Ls [ Beish, 1999].
Classically, the storms occurring during southern summer are larger and more dramatic, and can even grow rapidly to enshroud the whole planet. It should be remembered, however, that these global dust storms are quite rare – only ten have been reported since 1873, and all but two have occurred since 1956. However, two southern hemisphere encircling storms recorded by the Viking Spacecraft in 1977 and a southern hemisphere encircling storm dust storm was recorded by ground-based observers in 2001 that could be argued to be global. Much more common are the "localized" dust events, often starting in desert regions near Serpentis-Noachis, Solis Lacus, Chryse, or Hellas. During the 1997 apparition, CCD and HST observations revealed localized dust clouds over the north polar cap early in northern spring.
Identifying the places where dust storms begin and following their subsequent spread is most important to future Mars exploration missions. The following criteria apply in the diagnosis of Martian dust clouds:
A little understood phenomena
is when the surface features of Mars can be seen and
photographed in blue and violet light for periods of several
days to weeks at a time. Generally, dark surface features are
not identified in blue light; the surface albedo is almost
uniform everywhere in blue. However, they are occasionally
visible in blue. This phenomenon has been called "blue
clearing" for years and was reclassified as “violet
clearing” by Charles Capen in the early 1980’s. Capen found
that the spectral response of the W47 filter is pronominally in
the violet range and concluded that the phenomenon be called
Ironically Capen wrote in ALPO Mars Section newsletter and Journal, with similar comments by Lowell astronomer Leonard Martin, that this phenomenon had not been detected by our spacecraft camera filter systems in the 380-420 nm range; further deepening the mystery. A reasonable and recent description of “violet clearing” can be found in "The opposition of Mars, 2001: Part I," by Richard McKim, J. Br. Astron. Assoc. 119, 3, 2009, pp 113-114. http://www.britastro.org/mars/images/mars20011.pdf
The clearing can be limited to only one hemisphere and can vary in intensity from 0 (no surface features detected) to 3 (surface features can be seen also in white light). The Wratten 47 filter or equivalent is the standard for analyzing blue clearing. Normally the surface (albedo) features of Mars appear vague through light blue filters, such as the Wratten 80A. With a Wratten 47 dark blue or violet (380-420 nm) filter, the disk usually appears featureless except for clouds, hazes, and the polar caps.
THE INTERNATIONAL MARS PATROL
The International Mars Patrol (I.M.P.) is a cooperative program by planetary observers located around the Earth making it possible for a 24- hour surveillance of all Martian longitudes. Observers were located in 64 foreign countries and U.S. territories. Established in the 1960’s, by Charles F. ("Chick") Capen, the I.M.P. has contributed more than 42,388 observations of Mars by 1,074 individual amateur and professional observers. A typical apparition netted an average of 1,940 observations from an average of 79 amateur and professional observers. Contained within the archives of the A.L.P.O. Mars Section library are the records of twenty four apparitions of Mars covering a span of 50 years (August 1962 – June 2012).
NOTE: Modern technology, like CCD and webcam digital cameras, has greatly increased the efficiency even of small telescopes that in the past were considered less than optimal for serious planetary observing. Over the past decade an increased systematic use of color filters and modern CCD technology has led to renewal of interest in observing Mars. Many thousands of additional observations could be added to the table above; however, at this time the totals for the 2009-2010 and 2011-2012 apparitions have not been made available.
During the 1980’s and early 1990’s the I.M.P. participated in professional activities providing observers for Lowell Observatory’s International Planetary Patrol and provided quality photographs of Mars to the United States Geological Survey for creating maps of albedo features of the Red Planet. However, due to Federal budget cuts these programs have been severely limited to a narrow scope and amateur participation has all by disappeared.
The I.M.P. coordinates and instructs the cooperating observers in using similar visual, photographic (film and electronic), photometric, and micrometric techniques employing color filters and standard methods for reporting their observations. The chronological filing of this large quantity of data requires the observation information obtained for each night Universal Date be recorded on one or two standard observing report forms!
Each apparition the A.L.P.O. Mars Section receives thousands of individual observations consisting of visual disk drawings made with the aid of color filters, black-&-white and color photographs, intensity estimates of light and dark albedo features, color contrast estimates, and micrometer measurements of polar caps, cloud boundaries, and variable surface features during the 10 to 12 month observing period. The chronological filing of this large quantity of data requires the observation information obtained for each night Universal Date be recorded on one or two standard observing report forms!
It is with this regard that the
A.L.P.O. Mars Coordinators have prepared a simple, efficient
and standard Mars observing Report Form. This Standard Form, or
its format, can be used for reporting all types of observations
such as; micrometry, transit timings, intensity estimates, etc.
Photographs may also be attached to the top or back of the form
and the relevant information blanks to be filled in at the
telescope. Planetary aspects blanks can be filled in at other
times than while observing [ Capen et al,
The ALPO web page: http://alpo-astronomy.org/
The International Mars Watch web page: http://elvis.rowan.edu/marswatch/
The ALPO-Japan web page: http://alpo-j.asahikawa-med.ac.jp/Latest/Mars.htm
The Marsobservers Yahoo Mailing List: http://groups.yahoo.com/group/marsobservers/
The Mars Observer’s Café web page: index.html
Classical Martian Surface Feature Names and Location: names.htm
Antoniadi, E. M. (1930). The Planet Mars . Chatham: W&J Mackay, Ltd. p. 110.
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