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Mars Weather Report

Mars Today, created by Howard Houben of the Mars Global Circulation Model Group, is a poster produced daily by the Center for Mars Exploration at NASA Ames Research Center. The updated poster depicts current conditions on Mars and its relationship to Earth in six panels. The poster is available at www.mgcm.arc.nasa.gov/.

The upper left panel diagrams the current positions of Mars and Earth in their orbits around the Sun. Note the highly elliptical orbit of Mars compared to that of the Earth. A line is drawn from Earth to Mars; in this poster for September 12, 2000, we see that Mars is east of the Sun, in our morning sky. Also shown is the trajectory of Mars Global Surveyor. That spacecraft entered Mars orbit in 1997 and continues to provide much information on the Martian surface and atmosphere.

The upper middle panel shows two views of the positions of Mars and Earth from vantage points near the ecliptic. This allows visualization of the tilts of the rotation axes of the planets that are responsible for the seasons.

The panel on the upper right compares the apparent size of the Martian disc as viewed from Earth with the size of Earth's disc as viewed from Mars. (Since the diameter of Mars is about half that of the Earth, Mars appears to be about half the size of the Earth when viewed from the same distance.) Both of these discs are compared to a circle 25 seconds of arc in diameter. This circle represents the largest possible apparent size of Mars as viewed from Earth (which is achieved only on those very rare occasions when the planets are favorably positioned at the nearest points in their orbits). Even then, Mars—a very difficult telescopic object to observe in detail—is only half the apparent size of the much more distant, but much larger planet Jupiter.

At lower left hand is a simulated image of Mars as it would appear at the present time to a very high resolution Earth-based telescope. The lower middle panel shows a prediction of the meteorology at the present time. Daily average temperatures in the lower atmosphere are color coded, while predicted wind speeds and directions are indicated by the arrows.

The lower right panel shows model predictions of the atmospheric water vapor column on Mars. Statistics printed below the image indicate the apparent diameter of Mars (in seconds of arc), and other parameters.

A Mars Reading List

The Planet Mars: A History of Observation & Discovery, by William Sheehan, was published in 1996, and so it does not include everything there is to know about the fourth rock from the Sun, but it does a fine job in tracing the story of Mars that begins back as far in time as people have watched this red “wanderer.” An avid amateur astronomer and a psychiatrist, Sheehan is an ardent student of the planets. His previous books, published by the University of Arizona Press, including Planets and Perception and Worlds in the Sky, have won acclaim from the Astronomical Society of the Pacific.

Percival Lowell drew this sketch of Mars during the opposition of 1894. Plate XIX. Lacus Phoenicis.


Before presenting the history of Mars observation following the introduction of the telescope, a first chapter sets the basis for such narrative by explaining the motions of the planet in a clear and complete manner. The experiments of the principal astronomers are presented, citing Tycho Brahe, Johannes Kepler, Galileo Galilei, Camille Flammarion, Christiaan Huygens, Giovanni Cassini, and Giacomo Maraldi from the late 1500s through to the Mars opposition of 1719. William Herschel and Johann Schroeter made major contributions with their advanced telescopes, and in 1858 the first mention of canals was introduced by Angelo Secchi of Rome. The discoveries of Asaph Hall and Giovanni Schiaparelli take us to 1888 and the Lick Observatory, where Edward Holden observed with the new 36-inch refractor. It was the opposition in October, 1894, that brought Percival Lowell onto the scene, and the controversy over canals and life on Mars flared to a peak.

Several chapters tell the story of spacecraft to Mars. A chapter is devoted to observation methods for amateurs, and an appendix gives information about the planet and its oppositions. There is an extensive bibliography. This well-written book can be a useful companion for all who will become increasingly fascinated with Mars as new astronomical instrumentation and spacecraft further explore our neighbor. University of Arizona Press, 1996, 270 pages.

The Mystery of Mars is a book for children written by the first American woman in space, Sally Ride, and Tam O’Shaughnessy, a professor of school psychology. According to Sky & Telescope, “The text provides an overview of what we know about Mars, including a brief observational history of the red planet and a discussion of the possibilities of life. The image reproductions are excellent, which will surely make the views from Mars Pathfinder and Mars Global Surveyor a source of youthful wonder.” Crown Publishers, 1999, 48 pages.

The Search for Life on Mars, by Malcolm Walter, is a survey of astrobiological studies of Mars, including a discussion about Martian meteorites. Perseus Books, 1999, 170 pages.

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