A Guide to the

By

CHARLES H. SMILEY

and

JEAN ROBER TS

Ladd Observatory

BROWN UNIVERSITY

PROVIDENCE, R. I.

Co~Yright 1948 by Charles H. Smiley. Providence 12, R. I.

Moon

i

THE MOONBy CHARLES H. SMILEY

THE MOONis a lifeless body 2,163 milesin diameter, shining only by reflectedsunlight. Its distance from the earthvaries from 222,000 to 253,000 miles. Itsangular diameter as seen in the sky isapproximately half a degree. It possessesneither air nor water. The moon revolvesabout the earth in the same period as itrotates on its axis with respect to thestars; thus it always keeps the same faceturned toward the earth. Since 1608,when the invention of the telescope madepossible a detailed study of the moon, nochange in its surface has been noted.Among the surface features of the moonwhich can be observed with a pair offield glasses or a small telescope are thecraters, mountains, "seas," and rays.

There are about 32,000 lunar craterswhich are shown on the most detailedmaps of the moon. Of these, about 600 ofthe more prominent craters have beennamed after astronomers, philosophersand others. A list of these names and a brief accountof each of the persons thus honored have been pub-lished by the British Astronomical Association in"Who's Who on the Moon," and copied widely byothers. To explain the origin of the lunar craters,two major theories and many minor ones have beenoffered. The principal theories suggest that thecraters were formed by the action of volcanoes onthe moon, or by the impact of material striking themoon. The presence of a central peak in manycraters and the manner in which crater is piled oncrater will impress the observer; also notable is thelarge number of craters on the southern side of themoon.

SINUS IRIDUM..all. 16.000 It high

ER~TO$THENES,38

~RIST ARCHUS, 28bdgh...1 opal on Mo.n

COPERNICUS, 56

KEPLER, 22

GRIMALDI. 147on. of dorku' cro'",

SCHICKAR D, 134

A. MARE TRANOU/LtrAT/S E.MARENU81UMe. MARE FECUNO/TATIS F. MARE HUMORUMC MARE NECTARIS G MARECh/S/UMD. MARESEREN/TAT/S H. OCEANUSPBOCELLARUM

, MARE IM8R/UM

EUOOXUS, 40

ARIIITILLUS,54

AUTOLYCUS, 25

PROCLUS, ..

LANGRENUS,85

GASSENOI,55 VENOELIIIUS, SO

PETAYIUS, 100

WARGEIITIN. 114

STRAIGHT WALL,60 mil.. long. SoD" high

LONGOMONTANUS, SO.", d'.p

Besides the individual peaks in craters, there area number of mountain ranges on the moon whichhave been named after mountain ranges on theearth, for example, the Alps and the Apennines.Some of the mountains on the moon are as much as25,000 feet above the surrounding terrain. Themountains and craters are best seen when the moonis near first_or third quarter; shadows then serve tomeasure heights and depths.

The "seas," or maria as they were called in Gali-

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leo's day, are large relatively smooth areas of solidmaterial. That they are not bodies of water caneasily be seen with even a small telescope; they aremarked by small craters.

The rays are narrow light streaks radiating fromsome of the deeper craters. They are best seen at ornear full moon. The crater Tycho in the southernpart of the moon has one of the best ray systems;some of its rays exte~d a quarter of the way aroundthe moon.

Rills are narrow, crooked, deep valleys whichoften run several hundred miles along the moon'ssurface. None are shown on the maps presentedhere, since to- see them, one needs an instrumentmore powerful than a pair of field glasses.

The observer will enjoy watching changes in theappearance of the moon from night to night as theterminator (or line between light and dark portionsof the moon) moves westward. If one finds this in-teresting, one may wish to make or to purchase amoderate-sized telescope, perhaps a reflecting tele-scope with a six-inch mirror of approximately 50inches focal length. In such a case, a larger map ofthe moon will be needed.

The Maps of the MoonThe two maps presented here were designed as an

introduction to the moon, to be used by personspossessing field glasses or small telescopes. Noeffort has been made to show every detail of themoon's surface. They were prepared at Ladd Ob-servatory of Brown University in 1945 by MissJean Roberts under the direction of ProfessorCharles H. Smiley. They were originally intended

for men in the United States Armed Forces stationedat remote, relatively inactive posts. They appearedfirst in Science News Letter of March 3, 1945, in-cluding the Overseas Edition. They are reprintedhere by special permission of Science Service.

The numbers opposite the names of craters onthe index map indicate the approximate diametersof the craters in miles.

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