POPULAR ASTRONOMY

Otago Witness, Issue 2808, 8 January 1908, Page 13

POPULAR ASTRONOMY

NOTES FOR JANUARY. Bt Ret, D. Dutton, F.R.A.S., F.G.S. The Sun enters the sign of Aquarius" on the 21st, and will be in the constellation of the same name from the middle of February.- to the middle of March. There will be a total eclipse of the Sun on the 4th. No part of this eclipse" will be vieible in New Zealand. ' The Moon will be new on the 4th.~ first quarter on the 11th, fulL on the 19th, last quarter on the 27th. __ Of the," planets,- Mercury _- is~" a, morning, star, and"- Venus" is atf evenmg^star.^'easily Been in t "the south-western sky after sunset. The lingering twilight diminishes its appa- , rent brightness. Mars is a evening star, setting j^onXafter.- 10 o'clock. |Jupiter is now beegmSg -a is easilyfeseen in the north- west', rather late in the Saturn i 6 not far- from Mars, and sets' near .the same time. "*~ Of the' principal 'constellations, looking southward, the Cross will be seen between south-east, and south: The pointers — Alpha and Beta Centaiuri-^ire on the right-hand side of ; the Cross, lower down, and. nearer the souths Argo (the. Ship) is between east and south-east. Canopus is at a high altitude in al,south-easterna I , south-eastern direction; Achernar is -in the opposite direction, lower down than Canopus.' '. 'The long and inconspicuous constellation Hydra (the Serpent) stretches-, along the horizon from northeast to squth-east. Its chief star, Alphard (the "Solitary One"), is of the second magnitude. Orion, is' now showing at its best as ijt; moves up toward the meridian ; Betelguese and .Rigel, both of the first magnitude, arg its *■ principal ■ stars. The former is a variable 'star" falling at times < below the brightness of Rigel. In 1852 it was said/3to be the most brilliant/ star in the nortifernt."'-"flky7~',tffnd - ■wasu'again. bright in 1894., _,Betelguese marks the right shoulder *oT OKo'nV"' while "Riger represents his left "foot. ..This shows that in our sfev I the giant is heels over head. To the left of Betelguese is- Bell&trix, ' a second magnitude star, which marks , the left shoulder of "Orion. This constellation, \ both from the.tijtne.of its^ appearance — the winter— and froni its threatening, gesture was from the, earliestjtimes held to portend tempests and "disasters, and was, therefore, greatly .dreaded by the " v ancient mariner." Frequent references to its stormy character are found in classical literature. Polybios, the Greek historian, attributed "the loss of ships sustained by the Roman squadron in " the first Punic war to its having sailed " just >after, the rising of Orion," and in Milton's '."Paradise Lost" we have these lines : — "When with fierce winds Orion, armed, I _ Hath vexed the Red Sea. coast, whose waves i

o'-erthrew Bueiria and his Memphjan chivalry. In 18071 the University of Leipzig actually resolved; "that all the stars forming the belt and sword of Orion should henceforth be known only by the name of Napoleon." To this the English retaliated by proposing to call them Nelson. Fortunately the old name was too firmly established to be displaced. . Orion it fcas been from time immemorial,' and Orion it is likely to remain as long as its stars continue to shine. Taurus (the B.ull) shows splendidly in the north, with the Pleiades lower down, a little to the north-west. Canis Major-, with , N Sirius leading, is moving from the east towards the zenith. Cams Minor is easily recognised between east and northest. A distance from Procyon, the principal star, is Beta, and the contrast between these stars in brightness assists the observer in locating this constellation. In the north-east, Gemini (the Twins) is coming into view. The two principal stars are Castor and Pollux, the latter being the brighter. These stars, which are always associated in the popular mind, are said to ■be drifting apart. Pollux is coming towards us- at the rate of about 25 miles a second, while Castor is receding at about the same speed. Though the bond betweeri them 'is'-apparently close, they are in reality widely separated. Castor flashes f its beams to us in a little over 16 years, but 54 years at 'least are required for the rays of Pollux to reach us. The Twins have always been regarded as the special guardians of ■ those "who go down to the sea in ships," " a welcome couple to a vexed •barge." They were frequently adopted- as figure-heads of ancient ships. It will be remembered that when St. Paul sailed from the of Melita, where hehad been shipwrecked, he departed in "a ship of "Alexandria, whose sign was Castor and Pollux." Castor is" a splendid double star, its companion being' only one magnitude less than -its primary.

ITEMS OF INTEREST.

Many-^will follow with great interest the expedition to Flint Island, which left Auckland recently to observe the approaching total ■ solar eclipse, and will wish its members all the success that their enterprise and intrepidity deserve. The many possible chances of failure in connection -with' suehj expeditions fully justifies Governments -and scientific societies in their un■willingness to . incur the great expense of sending parties-jto such distant and out-of-the-way places. In connection with the total eclipse of the Sun which occurred on May 18; -1901, - ohe of the largest and best equipped expeditions was sent by the United' States Government to Sumatra. There were 11 astronomers, each a. specialist in 'his own department, and they took with them about 15 tons of instruments. 1 They were taken to their distant station by a Government steamer. They spent several weeks .in -preparation for the event; each man knew what he had to ''do, and took care to thoroughly, drill himself in. the quick manipulation of. the instruments he would have to, use when the important moment *bf totality should arrive. . Nothing that money and skill could supplywas wanting. The time of the eclipse was eagerly a-walted with jrreat expectation, -not ■unmixed with v trepidation. Alas! w&en it canie, the sky was covered with Clfinds,and as..-the time for the eclipse drew" near it was " seen that- there -was no "hope of a clears sky. ' The eclipse passed;-' and .as Professor Barnard said, " " The: / "b<^ t preparations ever made for the ohsSrva ions of a total eclipse of the San came to" naught.". t . . , _ A total eclipse of the S^n is one of the yrandelt and most aw^inspiring sights iShat Nature has" to offer* To the astronomer tne occasion is 'an opportunity of increaatojr his knowledge of the immediate , surrourMings of the^Sim, which at other times are invisible*' Totality can only be seen vfoen the observer is in . a place •wept over by tfe central shadow of the

Moon. This is a long, narrow line less than 170 miles in breadth. The penumbra of^ the shadow may reach several thousand miles, and anyone within its area will" witness a partial eclipse, varying in extent according to the distance he may be from •the central shadow paliST"- The average" "velocity "of the -Moon's* r tshad6w is shout 2100 miles per hour from west to east. This speed, may, however, be modified considerably, as, for.- .instance, when the ( shadow falls very obliquely, as'-is,the case j when "the "occurs near sunrise or J sunset L The Eai'th, also, in its- revolution, "i carries the spectator along in the same i direction as the Moon's- shadow is travel- j ling. At the equator, with a high Sun j and Moon, the Earth's jnotion subtracts ; about 100G miles -an. hour"-, from the speed i at which the shadow passes by ; totality, therefore, lasts longer in regions near the equator than elsewhere, but even under tihe most favourable conditions it is never prolonged to eight minutes.- There are" very few cases where totality has exceeded five or six minute 3. _ Every second is precious, a,rid it shows ' great skill in the manipulation "of instruments to enable observers to obtain the splendid results ! they have secured in such brief_ time. Photographs of the corona and prominences are taken, the structure of the inner" portions of the corona is diligently observed through the telescope. Spectroscppic observations of the corona, the prominences, and the chromosphere are made, and the region in the neighbourhood of the Sun is searched by telescope and camera for possible small planets between Mercury and^ the Sun — a search hitherto without success, though on several occasions individual observers have claimed the discovery of such bodies. These are some of the varied items of work mapped out beforehand, which must \be crowded into the few precious minutes of totality. There are enthusiasts in every branch of j science, but none outrival the astrono- ! mers.

• • The object of greatest interest to the astronomer in a total eclipse is the mysteri ous corona, an appendage of the Sun, which can only be sesn on tuch occasions. There is as yet no altogether satisfactory explana- ! tion of its nature. Our knowledge of it, as ' Sic R. Ball says, is of a somewhat .meagre description. Some results, however, have been obtained from former observations, and we "know rhat it is a true solar appendage, and that its condition is of a composite character, partly made up of selfluminous gases, chiofly hydrogen, and partly of incandescent solid or liquid particles shining both with reflected and inherent light Probably it represents matter in a constant fctate of •fffflux from and influx to the Sun under the influence of electrical repulsion in one direction and' of gravity in the other. Its materials' must be of in- ( conceivable tenerity, since comets, which are exceedingly light bodies, have at_ times cut Their way through millions of miles of coronal stuff Without any apparent ■ retardation. Since the eclipse of 1870, succeeding eclipses" have demonstrated that the marked Variations in its shape have a close connec-, i tion with, the 11-year period of sun spot activity. When spots on the Siun are 'numerous the corona is more fully de- [ veloped all round the Sun, with an abund-, 1 ance of relatively short streamers. When the spots are at a minimum there is generally a vast extension of the coronal streamers. Formerly, the solar prominences \ were visible only during a total eclipee, but in 1868, through the discoveries of Janssen and Lockyer, a method was devised by which the forms and movements of these j objects are brought under daily spectroscopic observation in the .observatories of the world. We hope that the more difficult proble.m of observing the corona without an eclipse will ere long be solved. A Russian astronomer, observing- from the top of "Mont Blanc in 1904, secured some photographs on which he believes the corona is represented. Unfortunately, this has not been confirmed.

Two solar eclipses occur ever year, and even five of some sort are possible, though this is a rare occurrence, happening once in about three centuries. There are three 6olar eclipses due this year, none of them visible in New Zealand. The last total eclipse of the Sun vieible in this country was in September, 1855, and many years must " pass before we are favoured with another.