THE Of all the secondary planets the earth's satellite is by far the most interesting and important. The moon completes her circuit around the earth in a period whose mean or average length is 27 days 7 hours 43.2 minutes; but in consequence of her 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. If the earth were motionless in space the moon's orbit would be nearly an ellipse, having the earth in one of the foci; hence her dis tance from the earth varies during the course of a lunar month. Her mean distance from the earth is 238,857 miles. Her maximum distance, however, may reach 252,715 miles, and the least distance to which she can approach the earth is 221,466 miles. Her diameter is 2,160 miles. and if we deduct from her distance from the earth the sum of the two radil 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 216,423 miles. Her orbit is a very intricate one, because the earth in moving around the sun carries the moon along with it; hence the latter is sometimes within and sometimes without the earth's orbit. Its form is that of a serpentine curve, always cmcave toward the sun, and its plane is inclined to the plane of the earth's orbit at an angle of 5° 9', in consequence of which our satellite appears sometimes above and sometimes below the plane of the earth's orbit, through which she passes twice in a revolution. 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 21 hours 22 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, which was well known to the ancients, MOON. who called it the Saros, and which was made use of by them in roughly predicting eclipses. The moon always presents the same face to us, as is evident from the permanency of the various markings on her surface. This circumstance proves that she revolves on an axis, and the time of rota tion 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′. In consequence of this fact the poles of the moon lean alternately to and from the earth. When the north pole leans toward the earth we see somewhat more of the region surrounding it, and somewhat less when it leans the contrary way. This displacement is known by the name of libration in latitude. By reason of irregular motion in her orbit, we see more of her eastern or western edge at one time than at another. This phenomenon is known as libration in longitude. The moon's surface contains about 14,657,000 Her volume is 1-49 and her mass 1-81 that of the square miles, or nearly four times the area of Europe. earth, and hence her density is about 3-5 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: and therefore a body which weighs 6 pounds here would weigh only 1 pound there. 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 tideraising power of moon and sun being as 11 to 5. Astronomers cling to the old idea that the moon is a dead world, destitute alike of air and water. THE EARTH'S ATMOSPHERE. The earth's sensible atmosphere extends more than 100 miles in height. The condition and motions of this aerial ocean play a most important part in the determination of climate, modifying, by absorbing, the otherwise intense heat of the sun, and, when laden with clouds, hindering the earth from radiating its acquired heat into space. Of the great number of comets which have temporarily visited our solar system or have become permanent members of it none has surpassed Halley's in historical associations. It has a record dating back to B. C. 240; its visitations spread alarm and consternation throughout Europe during the Middle Ages, it was the first whose return was predicted by an Astronomer Royal of England, and will, therefore, for these reasons, be an object of great scientific interest for all time. Its periodic time is 76.8 years, and in April, 1910, it made the perihellon passage for the twenty-ninth time. ENCKE'S COMET. The second of the periodic comets to be discovered was Encke's, as Halley's was the first. Encke's Comet has the shortest period known-namely, about 40 months. The observed visitations, from January, 1819, to September, 1924, form an uninterrupted series, thirty-three in number. Encke's is unique among comets in that its motion is constantly accelerating and its period is decreas OTHER COMETS. ing in proportion, being now 1,203 days as compared with 1,205 days in 1819. At first this was ascribed to a resisting medium, but it is more probably due to repeated passage of the comet through a cloud of meteors. COMETS OF 1843 AND 1882. brilliant enough to be seen by day with the unaided In the last 100 years only two comets have been eye. Of these one was in February, 1843, the other in September, 1882. Together with the comet of 1668 and that of 1887, hey form a comet group: each member, at periheilon, nearly brushes the sun's surface, that of 1843 having a velocity of 366 miles per second and passing halfway around the sun in two hours. These visitors are expected to return after six or seven centuries. The four comets were probably a single body until too close an encounter with the sun resulted in disruption. DONATI'S COMET. This was the finest comet of the nineteenth century and is known as the typical comet. In October, 1858, its tail reached halfway from the horizon to the zenith. Its period is 2,000 years. THE MOON'S PHASES, 1927. (Eastern Standard Time.) Atlantic time may be found by adding 1h.; Central, | found by subtracting 1h., 2h., 3h., 5h., or 5.5h., tantain, Pacifle," Alaska or Hawaii time may be respectively. Phase. | Da. THE MOON'S PHASES, 1927. Cent, Stan. T. M'nt'n Stan. T. Pacific Stan. T. Alaska Stan. T. Den.,S.L.C., Etc S'nF.,L'SA., Etc. Sitka, J'n'u, Etc, New Moon. 11 24 P.M. 10 24 P.M. Full Moon. First Quarter. Last Quarter..|24| 8 721 P.M. 6 21 P.M. 5 21 P.M. 4 21 P.M. 2 21 P.M. 16 MILLIKAN'S RAYS-OBSCURE COUSINS OF LIGHT. (From a Bulletin of the Smithsonian Institution, Washington, D. C.) The powerfully penetrating rays discovered by Millikan are invisible but, like X-rays, can penetrate metals. A thin sheet of lead, however, as everybody knows, will stop X-rays. Millikan's rays will travel through a layer of lead six feet thick. from the usual wave length down to as short as one centimetre, or 1,000 times Langley's longest. It seems that all space is alive with these new rays. They do not originate on the earth, but come in to us with the velocity of light from the great universe beyond the atmosphere. No one can yet foresee by what remarkable uses they may come to serve us. When Faraday, in 1831, demonstrated before the Royal Society that all that was necessary to obtain an electric current was to move a wire across the pole of a magnet, a woman in the audience asked him of what use the experiment was. That discovery, as we know, formed the basis of all modern electrical machinery. Faraday replied, "Madam, will you tell me of what use is a new-born babe?" The extraordinary penetrating power of the new rays depends on the extreme shortness of their wave-length. Ordinary broadcasting radio, or Hertzian rays, as everybody knows, have waves from 100 to 3,000 metres. Langley, years ago, found rays in the sun's and moon's beams, quite invisible to the eye, of a wave length of one-hundredth of a millimetre. German scientists later found that rays ten times longer than Langley's are sent out by special lamps, and they extended the radio region all the way The late Prof. Nichols, who died so tragically on the day the National Academy of Sciences building was dedicated at Washington, closed up the gap entirely between the longest lamp-rays and the shortest radio-rays. Light, such as we see with, consists of rays between the lengths 0.0004 and 0.0007 milimetres, and sun rays contain all varieties of rays from 0.0003 to 0.014 millimetres in wave length. Shorter sun rays than 0.0003 cannot reach us because of ozone in the high atmosphere, and longer sun rays than 0.014 millimetres are cut off by the water vapor which pervades the air. Air, indeed, even when freed from these gases, is very opaque to still shorter rays than 0.0003 millimetres. Yet by using vacuum apparatus Schumann, Lyman, Millikan and others have traced the lamp spectrum back to 0.00001-millimetre waves and beyond. After this we come directly into the domain of X-rays used in hospital practice. They run to 100 hundred times shorter still, or about 5,000 times shorter than yellow light. The new rays which Millikan has found are 2,000 tiraes shorter in their wave length than the average X-rays. What a gamut from these to radio! Yet all are alike in being just waves, and differ only in wave length. Some few affect us as light, but most are wholly invisible. We may call them the obscure cousins of light. E Orionis. Z Tauri. Z Orionis. K Orionis.. A Orionis (Betelguese).. B Auriga. B Canis Maj.. Auriga.. A Argus (Cano Dus) A Canis Majoris (Sirius). E Canis Maj.. 1.7 0.07 160 1.10.06 55 2 15.63 19 A Crucis... 3 49.4+31 40 Z Ursæ Majoris 3 54.5-13 43||A Virginis (Spica). 1.2 10.10 33 7 40.7+28 12 4.3-24 5 5.2-43 8 9 23.98 20 1.3 0.06 55 10 4.4 +12 20 150 10 15.8+20 13 5510 57.3 +56 47 6510 59.1 +62 9 50 11 10.1 +20 56 2.2 0.09 36 11 45.2 +14 59 2.5 0.02 150 11 49.9+54 7 1.1 0.02 150 12 22.4-62 41 2.8 0.03 100 12 30.4-22 59 2.9 0.07 50 12 37.9-1 2 1.5 0.01 300 12 43.3-59 17 0.2 0.10 A Centauri, 34 14 12.3+19 34 0.1 0.76 4 14 34.5-60 32 2.7 0.02 150 14 41.7 +27 23 2.2 0.04 80 14 50.9)+74 28 2.3 0.05 65 15 31.5+26 58 2.8 0.04 80 15 40.6+ 6 40 2.5 0.00 500 15 55.9-22 25 2.9 0.00 500 16 1.1-19 36 1.2 0.02 140 16 24.9-26 16 2.8 0.02 150 16 27.0 +21 39 1.9 0.03 100 16 40.7-68 54 2.4 0.04 80 16 45.3-34 10 2.6 0.03 100 17 6.1-15 38 1.7 0.01 300 17 28.5-37 3 A Ophiuchi 2.1 0.05 65 17 31.5 +12 37 5 54,6+37 13 I'Draconis 2.4 0.02 150 17 54.9+51 30 6 19.4-17 55||A Lyra (Vega) 0.1 0.12 27 18 34.5+38 43 A Aquila (Altair). 0.9 0.20 16 19 47.2+8 40 6 22.3-52 39|| гCygni.. 2.3 0.00 500 20 19.5 +40 1 A Pavonis. 2.1 0.01 300 20 19.7-56 59 6 41.9-16 37||A Cygni (Deneb). 1.3 0.01 300 20 38.9 +45 1 6 55.728 52 E Pegasi,.. 2.5 0.02 150 21 40.5+ 9 32 7 5.3-26 16 A Piscis Australis. 1.3 0.14 23 22 53.5-30 1 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. Thus, on January 1. Sirius is on the meridian at 12.00 P. M., approximately. ACanis Maj.. 1.6 0.37 9 Our universe-the space marked out by the distance to the outermost star of the Milky Wayis believed to be 350,000 light years across. A light year is the distance that light travels in a year, moving at the rate of 186,324 miles a second. It is the yardstick of modern astronomy. A light year is in round numbers six trillion miles, and the distance across our universe is taken as 350,000 times six trillion miles. RIGHT ASCENSION OF MEAN SUN, 1927. R. A. R. A. Date. H. M. May 21 20 0.2 12 23 17.3 Feb. 10/21 19.1 20121 58.5 1119 20.8 11 1 15.6 June 10 5 12.2 Aug. 9 9 8.7Oct. The R. A. M. S. increases at the rate of 3.943 minutes daily. H. M. 813 5.3 Dec. 715 3.6 17 15 43.0 27 16 22.4 7 17 1.8 17 17 41.3 MAGNETIC DECLINATIONS. Or Variation of Compass for January, 1927-With the Annual Change in 1925 for Places in the U. 8. A plus (+) sign to the annual change denotes that the declination is increasing, and a minus (—) sign the reverse. (Specially prepared for The World Almanac in the office of the United States Coast and Geodetic Survey.) Kiska.. 51 E -3 Ariz... Prescott.. Yuma. Ark Cal... Col... Del. Nogales. -1 Lincoln.. Concord.. 38 35 92 09 7 02 E 38 38 90 16 4 47 E 39 07 94 38 9 03 E 46 37 112 02 19 44 E 40 49 96 42 9 46 E 41 16 95 58 9 16 E 39 10 119 46 18 08 E 39 31 115 58 17 30 E 43 12 71 29 14 59W 40 13 74 44 9 54W 35 41 105 57 13 25 E Trenton.. 1 N. C.....Raleigh Santa Fe. 42 40 40 43 42 27 51 59 182 28 6 Conn.... Hartford. D. of C.. Washington. Fla.. Tallahassee. Jacksonville. 42 55 78 54 7 50W Yankton. Knoxville. Austin. San Antonio.. 29 27 98 28 9 46 E 41 54 87 37 2 35 E-4 R. I.. Me...... Bangor. Portland Eastport. Md.....Annapolis. Baltimore. Houston.. 123 08) 82 221 3 35 E +2 || H. I..... Honolulu. PrtoRico San Juan. 29 18 94 47 8 21 E 55 E 10 E 55 E 31 46 106 29 12 18 29 66 07 4 18W +7 P. I.....Manila.. FOO DURATION AVERAGES. The following table shows the average hours of fog per year at various U. S. Lighthouse Service Stations. |