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Plaintext
219 lines
13 KiB
Plaintext
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T h e M a r t i a n C h r o n i c l e
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July 1990 No. 3
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The electronic newsletter by the International Mars Patrol (IMP), an
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observing program of the Association of Lunar and Planetary Observers (ALPO)
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Edited by: J.D. Beish
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THE 1988 APPARITION OF MARS
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By the end of June 1989, the ALPO Mars Section had received more than
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1,000 letters and cards from interested amateur and professional astronomers
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located in 42 foreign countries and U.S. territories: Arabia, Argentina,
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Austria, Australia, Belgium, Bolivia, Brasil, Canada, Mainland China, Repub
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lic of China, Czechoslovakia, Columbia, England, Faroe Islands, France,
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Germany, Greece, India, Israel, Italy, Japan, Korea, Mexico, New Guinea,
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New Zealand, Norway, Nova Scotia, Okinawa, Philippines, Polynesia, Puerto
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Rico, Romaina, Rwanda, Scotland, South Africa, Somoa, Spain, Sweden, St.
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Croix, Taiwan, the USA, and Venezuela.
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The massive response to the most favorable Mars apparition in over a
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century is largely the result of the late Charles F. Capen's efforts in
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establishing the IMP. Because the IMP network was already intact, there was
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unprecedented international cooperation. Additional tactical support was
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provided by the Oriental Astronomical Association (OAA), the British Astro
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nomical Association (BAA),the Arbeitskreis Planetenbachter (Germany) and the
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Groupement International d'Observateurs des Surfaces Planetaires (GIOSP).
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A total of 411 telescopes were used by IMP Mars observers this appari-
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tion averaging 11.8 inches in aperture. Although most of the telescopes used
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by observers ranged between 3 to 16 inches in aperture, several astronomers
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employed reflectors of 20, 42, 60, and 90 inches and refractors of 6, 23,
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24, and 33 inches.
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By Jun 12, 1989, 304 observers from 22 countries had contributed 7,063
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quality Mars observations (4,818 drawings, 2,038 photographs, 16 CCD images,
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and 191 micrometer measurements), an indication of increasing interest in
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scientific study of the Red Planet. Included in the voluminous collection of
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observations were several VCR tapes with hours of images of Mars. A very
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successful observing program indeed!
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THE 1900 APPARITION OF MARS
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The ALPO Mars Recorders wish to thank those who participated and to
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extend our welcome to any one wishing to contribute observations during the
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1990 apparition. The ALPO Mars Section comprises of five Mars Recorders that
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have been assigned specific geographic locations and/or areas of interest.
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Those who are interested in participating in the International Mars Patrol
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and wish to receive the more advanced IMP newsletter, the Martian Chronicle,
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send 8 Self Addressed Stamped Envelopes (SASE) to the following ALPO Mars
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Recorder that reseides in your location:
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J.D. Beish, 9460 Toni Drive, Miami, Florida 33157 -- Alabama, Arkansas,
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Florida, Georgia, Hawaii, Kentucky, Mississippi, North Carolina, South
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Carolina, Tennessee, and Virginia.
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Harry Cralle, 3902 E. 29th Street (J-4), Bryan, Texas 77802 -- Arizona,
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California, Colorado, Kansas, Louisiana, Missouri, Nevada, New Mexico,
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Oklahoma, Texas, Utah, and Wyoming.
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Carlos Hernandez, 2714 Plaza Drive, Woodbridge, New Jersey 07095
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-- Alaska, Connecticut, D.C., Delaware, Massachusetts, Maryland, Maine, New
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Hampshire, New York, New Jersey, Pennsylvanian, Road Island, and Vermont.
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Don C. Parker, Coral Gables, Florida 33156 -- Overseas and U.S. Terri-
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tories.
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Dan Troiani, 629 Verona Ct., Schaumburg, Illinois 60193 -- Idaho,
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Illinois, Indiana, Iowa, Michigan, Minnesota, Montana, Nebraska, North
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Dakota, Ohio, Oregon, South Dakota, Washington, West Virginia, and Wiscon
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sin.
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Those wishing to join ALPO please write to: Harry D. Jamieson, ALPO
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Membership Sectretary, P.O. Box 143, Heber Springs, Arkansas 72543.
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DUST STORMS ON MARS
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What Mars may lack in white clouds and hazes during its southern spring
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and summer is more than made up for by one of the most spectacular phenomena
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seen in nature -- the great Martian dust storms. The current apparition
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(1990) is termed "perihelic" because Mars will be close to the Sun (and
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therefore the Earth) when it is at opposition. At perihelion, which occurred
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on June 29 of this year, Mars is some 43 million kilometers closer to the
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Sun than at aphelion. Current theory holds that the resultant 40% increase
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in solar radiation provides enough thermal energy to raise dust and hold it
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aloft for prolonged periods. Thus when Mars is near perihelion as it is now,
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we frequently see dust clouds form which often spread with tremendous veloc-
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ities to cover large portions of the planet. Occasionally one of these
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storms will have enough energy to cover the entire planet and is termed a
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"global" dust storm. Such massive obscurations occurred in 1956, 1971, 1973,
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and 1977 (two storms).
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While numerous dust clouds have been seen on Mars in the northern
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spring and summer, extensive and long-lasting dust storms are extremely rare
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for these seasons. Transient or short lived and small dust storms have been
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reported in past but they were observed to last only a few days and did not
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expand or move about very much.
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Much has been written about the characteristics of these dust clouds
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and how to detect them. These dust clouds are very difficult to identify in
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their beginning stages and, in some cases, go undetected even after they
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have fully developed. On the other hand, some observers have confused bright
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Martian desert regions or bright fog areas with dust clouds. Others see the
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bright orographic clouds in Tharsis as dust clouds. While many observers
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accept that the yellow-white appearance of some clouds indicates the
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presence of dust particles, they should not classify all bright clouds that
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appear to be yellowish as "dust clouds."
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THE COLOR OF MARTIAN DUST CLOUDS
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In the past, astronomers have identified Martian dust clouds and/or
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obscurations as "yellow clouds." Confusion over the colors of Mars is
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nothing new. Observers often report several of Mars' darker albedo features,
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or "maria," to appear quite green or even blue at times. This has led scien-
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tists of the past to speculate that vegetation grew on Mars during its
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springs and early summers. When we observe bright Mars against the dark
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nighttime sky, the planet's color hues are often perceived as complementary
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to the dark background sky. This effect is known as "simultaneous contrast"
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[See Sky & Telescope, May 1989, p.474, "What's New on Mars?" by William K.
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Hartmann].
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If we consider that Mars only varies from a dark gray-orange/brown to a
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slightly brighter grayish-orange or grayish-brown, it becomes interesting
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when attempting to describe the color of Martian dust clouds as "yellow."
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While dust clouds may appear yellowish when observed without the aid of
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color filters, they are in fact brighter in red and orange light than they
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are in yellow light. Thus it may be necessary to reclassify these clouds as
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simply "dust clouds."
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Martian dust clouds usually form rapidly when finely divided surface
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materials are raised by the Martian wind. These clouds may be small, local-
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ized, and short lived, or they may expand to cover most or all of the planet
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in a matter of days. Dust clouds brighten faintly in yellow filters and
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reveal sharpened boundaries through orange and red filters. During the
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initial stages of formation, they often appear very bright in violet and
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ultraviolet light (photographic), suggesting the presence of ice crystals.
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Thus dust clouds are frequently confused with bright white areas, frosts, or
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high localized clouds on Mars. Because these dust clouds are often confused
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with bright surface deposits it becomes more difficult to determine the
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extent of the dust cloud expansion once the observer identifies it as dust
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on the move. Fresh surface deposits of dust tend to brighten the area where
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its has fallen and appears to colease with the dust cloud on the move.
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In recent years, the popular media has played up the romance of Martian
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dust storms to such an extent that virtually any form of meteorological
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activity has been reported as dust. Therefore, in analyzing your observa-
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tions, the ALPO Mars Recorders have had to exercise considerable caution in
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defining dust clouds. We have applied the following criteria:
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1. The sine qua non of Martian dust clouds is movement with obscuration
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of previously well-defined albedo features. Absence of this criterion in the
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present study disqualified a candidate from inclusion under dust clouds.
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2. They are bright in red light.
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3. When these clouds reach heights of several kilometers, we have
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proposed that they may cast shadows -- that are observable from Earth.
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There are numerous reports of anomalous transient dark surface markings
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appearing near dust clouds, especially when the solar phase angle was rea-
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sonably large.
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THE NOT-SO-RED PLANET
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Further evidence for a dusty Martian atmosphere is not nearly so sophis-
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ticated as that obtained by professional instrumentation. In fact, it comes
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from "the man on the street!" In 1988, we received numerous phone calls and
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letters from nonastronomers as well as from experienced observers stating
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that Mars is not red this year, but rather orange, even when it is near the
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horizon. During the 1988 apparition, however, Mars' contrast was subdued
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more than "usual" and visual and photographic colorimetry do indeed reveal
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frequently greenish hues. Perhaps the most compelling evidence for the
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presence of persistent dust in Mars' atmosphere comes from observations the
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most prominent feature on the planet -- the South Polar Cap.
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ALPO GUIDELINES FOR MARTIAN DUST CLOUDS/STORMS
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New guidelines have been established by the ALPO Mars Recorders for
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interpreting Martian dust clouds/storms, they are as follows:
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I. Type of Observation.
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1. White cloud or bright area mistaken for dust cloud.
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2. Visual observation(s) of dust cloud or storm.
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3. Instrumental observation(s) of dust cloud/storm (Includes
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photographic, polarimetric, spacecraft data, or other data by
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instrumental means).
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II. Classifications of Martian dust clouds.
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1. Obscuration - Not sure if surface or atmospheric.
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2. Dust Haze - Partial obscuration with displacement.
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3. Bright dust cloud - Bright obscuration with displacement.
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4. Limb projection/terminator protrusion by dust cloud.
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III. Classifications of a Martian dust storm.
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1. Local: Dust storm with major axis not to exceed 2000 km.
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2. Regional: Dust storm with major axis that exceeds 2000 km in
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either or both hemispheres of Mars.
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3. Planet Encircling: Dust storm with major axis that completely
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encircles either one or both hemispheres of Mars.
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OBSERVING AIDS
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The physical and geocentric positions of Mars is available in the "A.L.P.O.
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Solar System Ephemeris," send $6.00 (for those living in the U.S, Canada,
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and Mexico; $8.50 (for those in other countries) to: John E. Westfall,
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A.L.P.O. Director/Editor, P.O. Box 16131, San Francisco, CA 94116.
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"Introduction to Observing and Photographing the Solar System," by Thomas A.
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Dobbins, Donald C. Parker, and Charles F. Capen. Available from Willmann
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Bell, Inc., P.O. Box 35025, Richmond, VA 23235
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Also, see the latest news on Mars in the August 1990 issue of Sky&Telescope
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**********************************NOTICE***********************************
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The Mars Observer's Handbook is out of print and no longer available.
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ct brighter in red and orange light than they
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are in yellow light. Thus it may be necessary to reclassify these clouds as |