Glossary Aphelion The farthest distance from the Sun in the elliptical orbit of a planet, comet or asteroid. Apogee The point in the orbit of the Moon

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1 About the Author John Wilkinson is a science educator with over 30 years experience in teaching science, physics and chemistry in secondary colleges and universities in Australia. He is author of over 100 science textbooks. He completed his Masters degree and PhD in science education at La Trobe University, Australia. Throughout his life he has been a keen amateur astronomer and operates his own observatory from his backyard. J. Wilkinson, The Moon in Close-up, Patrick Moore s Practical Astronomy Series, DOI / , # Springer-Verlag Berlin Heidelberg

2 Glossary Aphelion The farthest distance from the Sun in the elliptical orbit of a planet, comet or asteroid. Apogee The point in the orbit of the Moon or artificial satellite at which it is farthest from Earth. Apparent magnitude The visible brightness of a star or planet as seen from Earth. Asteroid A small rocky and/or metallic object with a small size, often irregular, orbiting the Sun in the Asteroid Belt. Astronomical unit (AU) The mean distance between the Earth and the Sun, about 150 million km. Atmosphere A layer of gases surrounding a planet or moon, held in place by gravity. Axis The imaginary line through the centre of a planet or star around which it rotates. Basins Basins are the largest class of impact craters on the Moon. They measure between 300 and 2,500 km in diameter. They have strongly developed multiple rings, radial features, and massive ejecta blankets. Basins do not have central peaks. Celestial equator An imaginary line encircling the sky midway between the celestial poles. Celestial poles The imaginary points on the sky where Earth s rotation axis, extended indefinitely, points. Celestial sphere The imaginary sphere surrounding the Earth, upon which the stars, galaxies, and other objects all appear to lie. Comet A small body composed of ice and dust that orbits the Sun on an elliptical path. Constellation One of 88 officially recognised patterns or groups of stars in the sky. Core The innermost region (centre) of a planet or star. 299

3 300 Glossary Cosmology The branch of Astronomy that deals with the origins, structure and space-time dynamics of the universe. Crater A circular depression on a planet or moon caused by the impact of a meteoroid, comet or asteroid. Can be of volcanic origin. Crater chains Crater chains are rows of small craters, thought to be due to debris from major crater impacts, or where a train of comet material has hit the surface. Crust The surface layer of a terrestrial planet. Declination The angular distance of a celestial body north (+) or south ( ) of the celestial equator. Degree A unit of angular measure, equal to 1/360 of a circle. Domes Domes are rounded bulges due to volcanic forces below the mare surface; they are generally km wide. Earth One of the major planets of the Solar System. Earthquake A sudden vibratory motion of the Earth s surface. Eccentricity A measure of how far an object deviates from circularity. Defined as the ratio of the distance between the foci and the major axis of the ellipse. Eclipse The total or partial disappearance of a celestial body in the shadow of another. Examples: solar eclipse, lunar eclipse. Ecliptic The apparent path of the Sun around the celestial sphere. It is also the plane of the orbit of the earth around the Sun. Ejecta The surrounding material excavated during the formation of an impact crater. Electromagnetic radiation The name given to a range of radiations that travel at the speed of light. Includes infrared rays, ultraviolet rays, visible light, X-rays and gamma rays. Ellipse The oval path, closed loop followed by a celestial body moving under the influence of gravity around another body.

4 Glossary 301 Equator The imaginary line surrounding a celestial body, half way between its two poles. Faults Faults or scarps (Rupes) are due to subsidence of one section of the Moon compared to a neighbouring area. Galilean moons The four largest moons of Jupiter discovered by Galileo Galilei in They are in order of distance from Jupiter, Io, Europa, Ganymede, and Callisto. Ghost craters Ghost craters are the remnants of very old craters that have been nearly obliterated by later lava flows. Graben A valley which has been formed by the sinking of land between two roughly parallel faults. Such a valley is long in proportion to its width. Gravity A force of attraction that exists between two masses. Hubble Space Telescope A telescope in orbit around earth. Ice Refers to solid states of water, methane, or ammonia which occur on planets, moons or asteroids. Impact basin Impact basins are the largest class of crater on the Moon being between 300 and 2,500 km in diameter. They also feature strongly developed multiple rings, radial features, and massive ejecta blankets. Inclination The angle between the plane of orbit of a planet and the ecliptic. Infrared radiation Form of electromagnetic radiation beyond the visible light region of the spectrum. Ion An electrically charged atom, either positive or negative. Ionisation The loss or gain by an atom of one or more electrons resulting in the atom having a positive or negative electrical charge. KREEP An unusual luna rock rich in potassium (K), rare-earth elements (REE), and phosphorus (P).

5 302 Glossary Lacus The word Lacus is used as a prefix in the names of lake-like features on the Moon s surface. These lakes are small circular or irregular dark areas in comparison to the larger, more readily seen maria. Lava Molten rock flowing on the surface of a planet. Libration The lunar libration is the apparent wobble (side to side and up and down motion) shown by the Moon as it orbits the Earth. Libration allows us to see up to 59% of the Moon s surface rather than only 50%. Lunar phase The amount of illuminated area on the Moon from reflected sunlight as seen from Earth. Magnetic field A region of force surrounding a magnetic object. Major axis The longest diameter of an ellipse. Mantle An inner region of a planet or moon that lies between its outer crust and central core. Mare A plain of solidified lava on the surface of the Moon that appears darker than the surrounding area. Mare is the latin name for sea as these plains were once thought to be. Maria Are dry, lava filled basins that appear as dark patches on the Moon s surface. Maria is latin for seas ; the singular form is mare. Mascon A mascon (mass concentration) is an area on the Moon containing a large positive gravitational anomaly. Mass The amount of material in a body. Usually measured in grams or kilograms. Meteor The bright streak of light that is seen when a rock or piece of space debris burns up as it enters Earth s atmosphere at high speed. Meteors that hit the Earth s surface are called meteorites. Meteoroid Any small debris travelling through space, usually from an asteroid or comet.

6 Glossary 303 Mons Mons is a latin word used in naming mountains on the Moon s surface, e.g., Mons Pico. Montes Montes is a latin word used in naming mountain ranges or grouping of mountains on the Moon, e.g., Montes Alpes. Moon The only natural satellite of the Earth. Takes about 28 days to orbit the Earth once. Nuclear fusion A process whereby light atomic nuclei (e.g., hydrogen or helium) combine to produce heavier nuclei, with the release of energy. Occurs in stars but not planets. Nucleus A collection of ices and dust that makes up the solid part of a comet. Occultation The apparent disappearance of one celestial body behind another, e.g., an occulatation occurs when the Moon passes in front of a planet or star. Oceanus Oceanus is a prefix used in naming ocean-like features on the Moon s surface. Such features are not oceans as on earth but large mare regions, e.g., Oceanus Procellarum. Orbit Path of one celestial body when revolving around another. Perigee The point in the orbit of the Moon or artificial satellite at which it is closest to Earth. Perihelion The closest distance to the Sun in the elliptical orbit of a comet, asteroid or planet. Period The time taken for a planet to orbit the Sun or a moon to orbit a planet. Phase The amount of illuminated area on the Moon from reflected sunlight as seen from Earth. Planet A celestial body that is in orbit around the Sun, has sufficient mass for its selfgravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared its neighbourhood around its orbit. Protostar A star in its early stages of formation.

7 304 Glossary Protosun The part of the solar nebula that eventually developed into the Sun. Radio telescope A telescope designed to detect radio waves. Radio waves Electromagnetic waves of long wavelength. Regolith Regolith is the soil on the lunar surface. It is made up of a complex layering of ejecta materials consisting of fragments of rocks and other materials excavated from meteoroid impacts. Retrograde motion The apparent westward motion of a planet with respect to background stars. Retrograde orbit An orbit of a satellite around a planet that is in the direction opposite to which the planet rotates. Revolution The motion in which a body moves around another body, such as the Moon around the Earth or the planets around the Sun. Rille Rilles (latin Rimae) are channels or groves on the Moon s surface. Some are collapsed lava tubes or crater chains, others (the sinuous rilles) are caused by lava flows from volcanic sources. Rock A mineral or collection of minerals. Rotation The spin of a planet, moon, satellite or star on its axis. Satellite Any small object (artificial or natural) orbiting a larger one, such as a body orbiting a planet. Selenography Mapping the surface features of the Moon. Semimajor axis The semimajor axis of an ellipse is equal to half the length of the major axis, which is a segment of a line passing through the foci of the ellipse with endpoints on the ellipse itself. The semimajor axis of a planetary orbit is also the average distance from the planet to its primary. Sidereal time The orbital period of a planet or satellite as measured with respect to the stars.

8 Glossary 305 Sinus Sinus is a prefix used in naming bay-like features on the Moon s surface, e.g., Sinus Iridum. Solar nebula The cloud of gas and dust from which the Sun and Solar System formed. Solar system The Sun, planets and their satellites, asteroids, comets, and related objects that orbit the Sun. Solar wind A stream of charged particles or ions emitted by the Sun and thrown into space. Space probe A spacecraft or artificial satellite used to explore other bodies (such as the planets or Moon) in the Solar System. Such a craft contains instruments to record and send back data to scientists on Earth. Space station A craft or vehicle that is in stable orbit around the Earth or other planet, that is the temporary home of astronauts. Spectroscopy The analysis of light from a planet or star to determine its composition and condition. Synodic month The time taken between two identical phases of the Moon, such as one new Moon to the next. Also known as a lunation. Tectonic forces Relating to the deformation of the crust of a planet or moon by forces within the body. Terminator The sunset or sunrise line on the Moon or a planet. Terrestrial planet A planet whose composition is mainly rock (Mercury, Venus, Earth and Mars). Transient lunar phenomena (TLP) Transient lunar phenomena or Lunar transient phenomena are unusual flashes of light, patches of clouds, and colour changes seen on the Moon s surface, especially around or inside craters. Valleys Valleys (latin Vallis) are thought to be due to rifts, where two areas have moved apart and the middle subsided. Weight The force of gravity acting on an object.

9 306 Glossary Wrinkle ridges Wrinkle ridges (latin Dorsa) are vein-like mare features created when basaltic lava cooled and contracted. They frequently outline ring structures buried within the mare. X-rays Electromagnetic radiation with short wavelength and high frequency (between ultraviolet and gamma rays) Zenith The point in the sky directly over an observer s head. Zodiac Name given to a group of twelve constellations that lie along the path followed by the Sun.

10 Index A Abulfreda crater, 208 Afocal photography, 158 Agatharchides crater, 274 Agricola Mountains, 283 Agrippa crater, 214 Albategnius crater, 222 Aliacensis crater, 229 Almanon crater, 208 Alpetragius crater, 222 Alphonsus crater, 223 Alps and Alpine valley, 92, 237 Altai scarp, 208 Altazimuth mount, 143 Apennine Mountains, 215 Aperture, 131, 137 Apollo lunar missions, Apollonius crater, 170 Appennine mountains, 91 Arago crater, 193 Archimedes crater, 237 Archytas crater, 239 Ariadaeus crater and rille, 194 Aristarchus crater, 95, 283 Aristarchus Plateau, 284 Aristillus crater, 239 Aristotle, 5 Aristotles crater, 239 Arzachel crater, 223, 229 Atlas crater, 187 Atmosphere of moon, 31 Autolycus crater, 239 B Ball crater, 229 Beaumont crater, 209 Bessel crater, 201 Bettinus crater, 244 Bianchini crater, 259 Binoculars, Birt crater, 230 Blancanus crater, 244 Blue moon, 111 Bode crater, 215 Bohnenberger crater, 177 Boscovich crater, 215 Brahe, Tycho, 5 Brayley crater, 285 Briggs crater, 285 Bulliadus crater, 275 Burg crater, 188 C Calippus crater, 240 Campanus crater, 275 Capture theory, 72 Capuanus crater, 275 Cardanus crater, 290 Carpathian Mountains, 264 Cassini crater, 240 Catharina crater, 209 Caucasus Mountains, 202, 240 Cauchy crater, 170 Cavalerius crater, 291 CCD cameras, 157,

11 308 Index Cepheus crater, 188 Chacornac crater, 188, 202 Chandrayaan space probe, 59 Chang e space probe, 58 Chromatic aberration, 137 Clavius crater, 245 Clementine space probe, 56 Co-creation theory, 71 Colombo crater, 178 Condorcet crater, 171 Conon rille, 215 Cook crater, 178 Coordinates on the moon, 28 Copernican period, 76 Copernicus crater, 265, 267 Copernicus, Nicolaus, 5 Craters, Cyrillus crater, 209 D Daedalus crater, 37 Daniell crater, 188, 202 Danjon scale, 123 Darwin, George, 60 Davy crater and chain, 223, 224 Dawes crater, 194, 202 Dionysius crater 194 Dobsonian mount, 143 Doppelmayer crater, 276 E Eclipses, 112 Ecliptic, Egede crater, 240 Ejecta, 22 Encke crater, 266 Equatorial mounts, Eratosthenes crater, 216 Eratosthenian period, 76 Euclides crater, 253 Eudoxus crater, 241 Exit pupil, 133 Eye relief, 134 Eyepiece projection photography, 158 Eyepieces, 141 F Far side of moon, 35, 101 Field of view, 133 Filters, 142 Firmicus crater, 172 Flamsteed crater, 253, 291 Focal length, 137 Focal ratio, 137 Foucault crater, 259 Fracastorius crater, 178, 210 Franklin crater, 188 Furnerius crater, 178 G Gaileo, 3, 5 Galileo crater, 291 Gambart crater, 267 Gassendi crater, 253, 276 Gay-Lussac crater, 267 Geber crater, 210 Geological structures, 86 Goclenius crater, 179 Godin crater, 217 Gravity on the moon, 29, 30 Grove crater, 189 Gruithuisen Mountains, 260 H Haemus Mountains, 194, 203 Harbinger Mountains, 285 Harpalus crater, 260 Helicon crater, 260 Hell crater, 230 Hercules crater, 189 Herigonius crater, 253 Herodotus crater, 285 Herschel crater, 224 Hesiodus crater, 230 Hevelius crater, 291 Highlands of moon, 87 Hippalus crater and rille, 84, 276 Hipparchus crater, 225 Horrocks crater, 225 Hortensius crater, 268 Hyginus crater and rille, 217 I Image processing, 162 Imbrium period, 75 Impact basins, Interior of moon, J Jansen crater, 195 Julius Caesar crater, 195 Jura Mountains, 260 K Kaguya space probe, 103 Kaguya space probe, 57 Kelvin scarp, 277 Kepler crater, 269, 292 Kepler, Johannes, 5 Kies crater and Kies Pi, 277

12 Index 309 Kircher crater, 246 Konig crater, 277 Krafft crater, 292 KREEP rock, 87 Krieger crater, 286 Kuiper crater, 254 L Lacus Mortis, 187 Lacus Somniorum, 187 Lamont crater, 196 Langrenus crater, 180 Lansberg crater, 254, 269 Large-impact theory, 72 Lassell crater, 225 Latitude and longitude, 27 LCROSS space probe, 32, 61 Le Monnier crater, 189, 203 Le Verrier crater, 261 Lee crater, 278 Letronne crater, 255 Lexell crater, 230 Libration, Lichtenberg crater, 286 Lohse crater, 181 Longomontanus crater, 246 Lubiniesky crater, 255, 279 Lunar craters, 22 Lunar domes, 83 Lunar eclipses, Lunar faults, 82 Lunar landings, map, 50 Lunar probes, table of, Lunar Prospector, 56 Lunar Reconnaissance Orbiter (LRO), Lunar rocks and soil, 77 Lunar valleys, 92 M Maclear crater, 196 Macrobius crater, 172 Madler crater, 210 Maginus crater, 247 Magnetic field of moon, 34 Magnification, 132, 138 Mairan crater, 261 Manilius crater, 217 Mare Cognitum, 20, 251 Mare Crisium, 18, Mare Fecunditatis, 169, 177 Mare Frigoris, 21, 236, 259 Mare Fucunditatis, 18 Mare geology, 82 Mare Humorum, 20, 272, 273 Mare Imbrium, 20, 236, 259 Mare Insularum, 263 Mare Nectaris, 18, 177, 207 Mare Nubium, 20, 222, 228 Mare Serenitatis, 19, 187, 193, 199, 236 Mare Tranquillitatis, 18, 170, 191, 193 Mare Vaporum, 20, 212, 213 Maria, 18 Marius crater and hills, 292 Marius Hills complex, 86 Mascons, 99 Maskelyne crater, 196 Menelaus crater, 196, 203 Mercator crater and scarp, 279 Messala crater, 189 Messier craters, 172 Metius crater, 181 Milichius crater, 270 Moon, filters, 21 rocks, 87 early views, 7 far side, 101 features, 18 history of, 74 interior, map, 19, 25, 27, 149 motion of, 9 observing, 148 orbit of, 4, 9 origin, phases, 14 water, 32 Moretus crater, 247 Mount Argaeus, 203 Mountains of moon, Mt Piton, 241 N Nectarian period, 75 Newton, Isaac, 6 Nicollet crater, 231 Norman crater, 255 O Occultations, 107 Ocean tides, 30 Oceanus Procellarum, 20, 252, 281, 290 Olbers crater, 294 Orientale basin, P Pallas crater, 217 Periods of moon, Petavius crater, 181 Phases of the moon, 14 16, 148 Photographing the moon, 155

13 310 Index Picard crater, 173 Piccolomini crater, 181, 210 Pierce crater, 173 Pioneer space probes, 42 Pitatus crater, 231 Plato crater, 241 Plinius crater, 197 Plinius crater, 204 Posidonius crater, 190, 204 Post-Nectarian period, 75 Prime focus photography, 157 Prinz crater, 286 Proclus crater, 173 Ptolemaeus crater, 225 Ptolemy, 5 Purbach crater, 231 Pyrenees Mountains, 182 R Ramsden crater, 279 Ranger space probes, 42 Reflecting telescopes, 139 Refracting telescopes, Regiomontanus crater, 231 Regolith, 77 Reiner crater, 294 Reiner Gamma, 294 Reinhold crater, 270 Rheita crater and valley, 92, 182 Riccioli crater, 294 Rilles, 82 Riphaean Mountains, 255, 256 Ritter crater, 197 Rockets to the moon, Ross crater, 197 Rosse crater, 182, 211 Rupes Recta, 85, 232 S Sabine crater, 197 Sacrobosco crater, 211 Santbech crater, 183 Saturn V rocket, 52 Scarps, 82 Scheiner crater, 247 Schiaparelli crater, 286 Schiller crater, 247 Schroeter crater, 218 Schroter s Valley, 96, 286 Secchi crater, 173 Seleucus crater, 287 Serpentine ridge, 204 Sharp crater, 261 Shoemaker, Eugene, 7 Sidereal and synodic month, 17 Silberschlag crater, 198 Single lens reflex phototography, 156 Sinus Aestuum, 218 Sinus Iridum, 20, 257, 261 Sinus Medii, 218, 226 Smart-1, 56 Snellius crater, 183 Soil breccia, 77 Solar eclipses, Space probes to moon, Stevinus crater, 183 Straight range, 262 Straight wall, 85 Sulpicius Gallus, 204 Surveyor space probes, 42 Synodic month, 17 T Taruntius crater, 173 Taurus Mountains, 190 Temperatures on moon, 33 Terminator, 26 Theaetetus crater, 242 Thebit crater, 232 Theophilus crater, 211 Tidal forces, 29 Tobius Mayer crater, 270 Transient Lunar Phenomena, 94 Triesnecker crater and rille, 218 Tycho crater, 23, 248 U Ukert crater, 219 V Vendelinus crater, 183 Video photography, 161 Vitello crater, 279 Vitruvius crater, 205 W Walter crater, 233 Water on moon, 32 Webb crater, 174 Werner crater, 233 Wichmann crater, 256 Wilhelm crater, 248 Wolf crater, 233 Wrinkle ridges, 82 Y Yerkes crater, 174 Z Zucchius crater, 249