272 SOLAR SYSTEM/Mars Table Lunar eclipses, 2004 2020 Date 2004 2004 2005 2006 2007 2008 2008 May Oct 28 Oct 17 Sept Mar Feb 21 Aug 16 Type Time of mid eclipse, GMT Total Total Partial Partial Total Total Partial 20.32 03.05 12.04 18.52 23.22 03.27 21.11 Duration of totality minutes Percentage of Moon eclipsed 38 40 100 100 18 100 100 81 37 24 Table The Danjon scale Very dark; Moon almost invisible at totality Dark grey or brownish, details barely identifiable Dark or rusty red, with a dark patch in the middle of the shadow: brighter edges Brick red, sometimes a bright or yellowish border to the shadow Coppery or orange red; very bright, with a bluish cast and varied hues Lunar eclipses may be either total or partial Because the Sun is a disk, not a point source of light, there is an area to either side of the main shadow cone (the umbra), through which the Moon has to pass; this region is termed the penumbra, and produces only a slight dimming of the surface Some eclipses are penumbral only The last eclipses were those of 16 May and November 2003; a list of umbral eclipses up to 2008 is given in Table No two eclipses are alike; everything depends upon conditions in the Earth’s upper air through which the sunlight has to pass If there is an unusual amount of dust, following an event such as a volcanic eruption, the eclipses is liable to be dark Observers use a scale given by A Danjon (Table 6) Lunar eclipses not happen at every new moon, because of the inclination of the lunar orbit Astronomically, they are not important, but they are certainly beautiful to watch, some displaying a wonderful range of hues See Also Analytical Methods: Geochronological Techniques Earth Structure and Origins Solar System: Meteorites; Mercury; Jupiter, Saturn and Their Moons; Neptune, Pluto and Uranus Tectonics: Earthquakes Tektites Further Reading Harland B (1977) Exploring the Moon Springer/Praxis Lindsay H (2001) Tracking Apollo to the Moon New York, Berlin: Heidelberg, Springer Verlag Massey H, et al (eds.) (1997) The Moon: A New Appraisal London: The Royal Society Moore P (2002) Patrick Moore on the Moon London: Cassell Schultz P (1976) Moon Morphology University of Texas Press Shepard A and Slayton D (1994) Moon Shot Turner Pub lishing Inc Taylor S (1975) Lunar Science Oxford: Pergaman Press Wilhelus E (1999) To a Rocky Moon Arizona: University of Arizona Press Wood CA (2003) The Modern Moon Sky Publishing Corp Westfall JE (2000) Atlas of the Lunar Terminator Cambridge: Cambridge University Press Rukl A (2001) Atlas of the Moon London: Hamlyn Mars M R Walter, A J Brown, and S A Chamberlain, Macquarie University, Sydney, NSW, Australia ß 2005, Elsevier Ltd All Rights Reserved Introduction Mars, the fourth planet from the Sun, is Earth’s second closest planetary neighbour As a nearby terrestrial planet with an atmosphere, it shares some geological processes with Earth However, our impressions of Mars are most clearly drawn into perspective by considering the differences between the geology of Earth and the geology of Mars Mars has an elliptical orbit, ranging from 207 to 249 million km from the Sun Earth is much closer to the Sun (147 to 152 million km) and therefore is warmer It takes 687 Earth days for Mars to orbit the Sun (670 Martian days, or ‘sols’) A day on Mars lasts 24 h and 37 The diameter of the planet is 6780 km, about half that of Earth Its surface area is about the same as that of the land area on Earth At present, its axis is inclined at 25 to the ecliptic (the plane of rotation around the Sun), much like Earth’s, and so it has similar seasons Compared to the northern hemisphere, southern-hemisphere winters on Mars are more intense; springs and