The moon completes a circuit around the earth in a period whose mean or average length is 27 days 7 hours 43.2 minutes; but in consequence of its motion in common with the earth around the sun. the mean duration of the lunar month-that is, the time from new moon to new moon-is 29 days 12 hours 44.05 minutes, which is called the moon's synodical period. The mean distance from the earth according to the American Ephemeris is 238,857 miles. The maximum distance, however, may reach 252,710 miles, and the least distance to which the moon can approach the earth is 221,463 miles. Its diameter is 2,160 miles, and if we deduct from her distance from the earth the sum of the two radii of the earth and moon-viz.. 3,963 and 1,080 miles, respectively-we shall have for the nearest approach of the surfaces of the two bodies 216,420 miles. The orbit's form is that of a serpentine curve, always concave toward the sun, and its plane is inclined to the plane of the earth's orbit at an angle of 4° 59' to 5° 18' the mean value being 5° 8. These points of intersection with the ecliptic are called nodes, and it is only at or near them that eclipses can occur. The nodes have a retrograde motion, which causes them to make an entire revolution in 18 years 218 days 23 hours 5 minutes and 46 seconds Both sun and moon return to a node after 18 years and 11 days, so that an eclipse is followed by another of the same general character at the end of this period. The moon always presents the same face to the earth, as is evident from the permanency of the various markings on her surface. This proves that the moon revolves on an axis, and the time of rotation is exactly equal to the time of revolution around the earth-viz., 27.32166 days. The moon's axis is not perpendicular to the plane of her orbit, but deviates therefrom by an angle of about 6° 41'. The moon's surface contains about 14,657,000 square miles; the volume is 1-49 and mass 1-81 that of the earth, or about 3 2-5 that of water. At the lunar surface gravity is only 1-6 of what it is at the earth. The centre of gravity of the earth and moon, or the point about which they both actually revolve in their course around the sun, lies within the earth. It is 1.050 miles below the surface. The tides are caused mainly by the moon, the tide-raising power of moon and sun is 11 to 5. A 9 6 42.616 38 300 0.1 0.76 33 14 13.0 +19 29 4 14 35.6-60 36 150 14 42.5 +27 19 80 14 50.9+74 24 2.3 0.05 65 15 32.2+26 55 2.8 0.04 80 15 41.4 6 36 2.5 0.00 500 15 56.9-22 27 2.9 0.00 500 16 2.1 -19 39 1.2 0.02 150 16 25.8 -26 18 2.8 0.02 150 16 27.7 +21 37 1.9 0.03 100 16 42.5 -68 55 2.4 0.04 80 16 46.4-34 11 2.6 0.03 100 17 7.0-15 39 1.7 0.02 150 17 29.7-37 4 2.1 0.05 65 17 32.2+12 36 2.4 0.02 150 17 55.3 +51 30 0.1 0.12 27 18 35.0+38 44 (Altair) 0.9 0.20 16 19 48.0 + 8 43 Cygni... 2.3 0.00 500 20 20.1 +40 4 Pavonis... 2.1 0.01 300 20 21.1-56 55 Cygni Joris (Sirius) -1.6 0.37 (Deneb.) 1.3 0.01 300 20 39.5 +45 4 E Canis Maj.. 1.6 0.01 6 56.328 54 E Pegasi...... 2.5 0.02 150 21 41.3 +9 36 A Canis Maj.. 2.0 0.01 300 7 6.0 26 18 A Piscis Australis 1.3 0.14 23 22 54.5-29 56 To find the time when star is on meridian, subtract R. A. M. S. of the sun table below from the star's Right Ascension, first adding 24h to the latter, if necessary; mark this result P. M. if less than 12h.; but if greater than 12h. subtract 12h. and mark the remainder A. M. Right Ascension of Mean Sun, 1942 (At Washington-Mean Noon) Date 31 20 41.2 April 1 0 37.7 Feb. 10 21 20.6 20 22 0.0 31 4 34.2 R. A. 11 1 17.1 June 10 5 13.7 Aug. 19 9 10.2 Oct. The Right Ascension of Mean Sun increases 3.943 minutes daily. 18 11 47.9 H. M. 28 14 25.6 715 5.0 17 15 44.5 27/16 23.9 7:17 3.3 17 17 42.8 Notable Telescopes Astronomical telescopes are of two kinds, refracting and reflecting. In the first, the light falls upon a lens which converges the rays to a focus, where the image may be magnified by a second lens, called the eyepiece, or may be directly photographed. The reflector consists of a concave mirror, generally of glass coated with silver or aluminum, which throws the rays back toward the upper end of the telescope, where they fall on the eyepiece or on the photographic plate, as in the case of the refractor. In some telescopes the light is reflected again by a secondary mirror and comes to a focus either to the side or after passing through a hole in the principal mirror. Since the rays of light do not pass through the mirror, far less perfect glass is required and reflectors can be made much larger than refractors. For many kinds of celestial photography reflectors are better than refractors. The largest refractors in the world are: 40-inch of the University of Chicago, at the Yerkes Observatory, William Bay, Wis. (62 feet long); 36inch of the University of California, at the Lick Observatory, Mount Hamilton: 3212-inch, in the observatory at Meudon, France: 3112-inch, in the astrophysical observatory at Potsdam, Germany; 30-inch, at Pulkova, Russia; 30-inch, Univ. of Paris, at Nice; 28-inch, in Royal Observatory, Greenwich, England; 30-inch photographic fractor of the University of Pittsburgh; the 26inch instruments at the U. S. Naval Observatory, Washington, and at the University of Virginia. re at The largest reflectors are: 74-inch, David Dunlop Observatory, University of Toronto, Richmond Hill, 12 miles north of Toronto, Can.; 72-inch, in the Dominion Astrophysical, Victoria, B. C. 69-inch, Ohio Wesleyan University, Delaware, O.; 100-inch, Carnegie Institution, Mt. Wilson, Calif.; 61-inch, Oak Ridge station of Harvard; 60-inch, Harvard Univ., in South Africa: 482inch, Berlin-Babelsburg, Germany; 42-inch, Lowell Observatory, Flagstaff, Ariz.; 3914-inch, Hamburg University, Bergedorf, Germany; 372-inch, Detroit Observatory of the University of Michigan, at Ann Arbor; 36-inch, of the University of California, in the Lick Observatory, Mt. Hamilton; 36-inch, University of California, at Santiago, Chile; 36inch, in the Steward Observatory, Tucson, Ariz. A new 82-inch reflector (dedicated May 5, 1939) is on Mt. Locke, near Fort Davis, Texas, financed jointly by the University of Texas and the University of Chicago. A 200-inch reflecting telescope, the largest in the world, is for the California Institute of Technology at Pasadena, California. It is located on Mt. Palomar, 5,565 feet elevation, 66 miles north of San Diego and 124.9 miles southeast of Pasadena. The 200-inch glass disk was poured on Dec. 2, 1934, at Corning, N. Y. The project was completed in July, 1939. The 74-inch reflector of the Dunlop Observatory has a glass of Pyrex. A 74-inch reflector is being made for the new Radcliffe Observatory at Pretoria, So. Africa. The mirror is of pyrex glass. The U. S. Naval Observatory, Washington, has a new reflector of the Ritchey-Chretien type, the chief characteristic of which is a larger field than is commanded by the usual type of reflector. When the instrument is used photographically it is necessary that the films or plates be somewhat curved in shape. Photographic refractions having a 2, 3, or 4 lens objective are smaller in size and shorter in length. The best known of these are: the 27-inch refractor of the University of Michigan, at Bloemfontein, South Africa; the 26-inch refractor of Yale University, at Johannesburg, South Africa, the 24-inch of the Harvard Observatory at its station in South Africa; two of 16 inches at Heidelberg and at the Harvard Observatory; and the 10-inch Bruce telescope at the Yerkes Observatory. The light-gathering power of a telescope is proportional to the area of its lens or mirror. The 40-inch Yerkes refractor increases the amount of light forty thousand times that received by the eye. The magnifying power of a telescope is proportional to the ratio of the length of focus of the large lens to that of the eyepiece. Thus the use of different eyepieces yields various magnifying powers, but those exceeding 1,000 are seldom used because of the trembling of the earth's atmosphere. Polar Star, 1942 Mean time of upper transit (at Washington) and Polar Distance of Polaris Upper transit of Polaris occurs, on the average, 3m. 56s. earlier each day. The interval between lower and upper transit of Polaris is 11h. 58m. 2s. At the latitude of Washington, D. C., the greatest Eastern elongation of Polaris occurs 5h. 56m. before 5 52 A.M.1 0 48 8 17 A.M.1 0 38 2 34 P.M.1 0 27 4 25 P.M.1 0 16 upper transit and 6h. 2m. after lower transit, while the greatest Western elongation occurs 5h. 56m. after upper transit and 6h. 2m. before lower transit. The Moon's Perigee and Apogee, 1942 (Eastern Standard Time. Perigee, 1942 A.M. light figures; P.M. black) Apogee, 1942 Each month the moon is said to be in perigee when nearest to the earth and in apogee when farthest from the earth. The average time from perigee to perigee, or from apogee to apogee, is 27d. 13h. 18m. 33s; known as the anomalistic month. Morning and Evening Stars, 1942 MORNING STARS Mercury-February 9 to April 20; June 12 to August 2; October 10 to November 30. Venus February 2 to November 16. Jupiter-June 25 to end of year. Saturn-May 23 to December 1. EVENING STARS Mercury-January 1 to February 9; April 20 to June 12; August 2 to October 10; November 30 to end of year. Venus January 1 to February 2: November 16 to end of year. Mars January 1 to October 5. Jupiter January 1 to June 25. Saturn-January 1 to May 23; December 1 to end of year. Table of Magnetic Declination Source: United States Coast and Geodetic Survey Values observed at selected points, reduced to January, 1942; also the annual change. reverse. A plus (+) sign to the annual change denotes increasing declination, and a minus(-) sign the (Specially prepared for the World Almanac in the Office of the U. S. Coast and Geodetic Survey. Further information may be obtained by addressing The Director, U. S. Coast and Geodetic Survey, Washington, D. C.) 46 37 112 04 18 56 E-2 40 50 96 40 9 40 E 0 41 16 95 58 9 02 E 0 39 07 119 46 17 55 E -1 39 31 115 58 17 15 E-1 43 13 71 32 15 39W+2 40 15 74 48 10 27W+1 35 41 105 57 13 26 E 0 42 40 73 45 13 36W+2 40 35 73 54 11 21W +1 42 56 78 52 7 34W 0 42 27 76 28 9 35W +1 35 47 78 39 4 16W 34 13 77 56 3 17W 46 49 100 47 13 47 E-1 48 58 97 15 9 27 E 39 08 84 31 0 42 E+2 41 28 81 37 4 57W 40 03 82 59 1 48W 34 23 96 09 9 06 E +2 35 53 97 25 9 59 E +1 45 31 122 43 22 51 E-2 40 15 76 53 8 32W 0 39 57 75 12 9 51 W +1 40 29 80 01 5 33W-1 0 0 40 E+2 24 E +1 11 E-1 2 24 E +1 Pa. Harrisburg. Philadelphia. R. I. Pittsburgh Providence. S. C..... Charleston.. 34 02 36 E +2 41 47 87 35 39 50 89 39 3 54 E+1 41 06 85 08 0 53W-1 39 48 86 12 0 41 36 93 34 7 22 E 0 40 23 91 23 5 25 E+1 38 28 99 54 11 20 E 0 39 02 95 43 9 13 E1 38 02 84 30 0 06 E +2 38 14 85 42 37 03 88 36 0 40 E+2 4 20 E+2 30 24 91 10 6 59 E +2 29 56 90 08 6 22 E +2 32 28 93 42 7 54 E 44 55 43 41 Columbia. S. D..... Pierre... Yankton. Tenn.... Knoxville. Memphis. Nashville Texas...Austin. El Paso.. Utah... Ogden. 0 Va.... 44 48 68 48 19 37W+1 67 00 21 38W +1 70 18 17 11W +2 38 59 76 30 7 42W 39 18 76 35 7 53W 42 20 71 01 15 24W+2 42 26 73 15 13 51W +2 42 20 82 58 2 45W 42 44 84 32 1 36W 46 33 87 23 46 44 92 03 44 58 93 06 32 20 90 12 34 22 89 32 0 26 E 7 05 E 7 40 E-1 6 44 E +2 5 55 E+2 38 34 92 11 7 01 E+1 39 01 94 32 8 59 E+1 38 39 90 18 4 47 E +2 Salt Lake City Vt....... Burlington.. Montpeller. Lynchburg. Norfolk.. Richmond. Wash... Olympia. Walla Walla. W. Va... Charleston. Wis..... La Crosse. Wyo....Cheyenne. TERRITORIES AND DEPENDENCIES Alaska.. [Dutch Harbor..153 53 166 32 16 27 E-2 || T. H.... Hilo. 81 03 0 03 E +1 44 22 100 21 12 10 E-1 42 53 97 23 10 40 E 0 35 57 83 57 0 35W 35 08 89 56 5 36 E+ 36 09 86 44 3 30 E 30 16 97 46 9 28 E 31 48 106 26 12 45 E+ 29 19 94 47 8 44 E + 29 43 95 23 9 07 E +2 29 29 98 32 10 11 E +2 41 10 111 58 17 43 E 40 47 111 52 16 54 E 44 28 73 12 15 01W 44 15 72 32 16 42W + 37 24 79 08 4 09W 36 52 76 16 6 19W 37 33 77 29 5 38W 47 03 122 53 23 12 E-2 46 04 118 23 21 12 E 38 21 81 38 3 15W 40 04 80 40 2 47W 43 50 91 14 4 28 E 43 04 89 25 3 49 E 43 04 87 52 2 12 E 41 09 104 52 14 44 E - 1 0 0 19 44 155 04 10 01 E+2 21 18 157 52 11 38 E +2 14 34 120 59 0 52 E+1 18 02 66 38 5 25W +5 18 27 66, 08 5 50W+5 Santiago.... 120 00 75 49 0 17 E) - 2 147 10 67 57122 36W 0|| Alaska.. | DemarcationPt.169 39 141 00:39 15 E Rate of Speed of a Falling Body Source: Aviation and Army Records. In the first second of its descent a body falls 16 feet; second second, 16 + 32 = 48 feet; third second, 16 +84 = 80 feet; fourth second, 16 +96 112 feet: Afth second, 16 +128=144 feet; nth second, 16+ 32 (n-1) feet. The total distance fallen by a body at the end of the nth second is given in feet by multiplying the square of the time in seconds by 16. Thus at the end of the first second it has fallen 16 feet, at the end of the second second 2 X2 X 16 64 feet, at the end of the third second 3X 3X 16 5 144 feet; at the end of the fifth, 5 X 5 X 16 = 400 feet. Conversely, to find the time in seconds to fall any distance, divide the distance in feet by 16 and extract the square root; thus to fall a mile divide 5.280 by 16, which gives 330, and the square root of 330 is a little over 18, the number of seconds which is the vacuum time to fall a mile. Owing to the resistance of the air, it takes about 19 seconds for a bomb to reach the earth when dropped from an airplane a mile high. |