LESSONS IN ASTRONOMY. 





on paper these divisions will necessarily be very small; when, 

 deal with a globe of tho size of the earth, we find 



thai u dr-i-oo at the equator measures ui nine miles. 



In a right :ui-l thro are, of course, ninety degree*, 

 wo uiako a trianglu \\Uli three equal aides, each angle will < ,. 

 uiin juat sixty degrees. A degree is divided int., uty parts, 

 culled minntea; each of these is divided into sixty pu.rU, called 

 ttcondi i and in more accurate observation* each of these ia 

 iividud into sixty parts, which are called third*. These 

 us are usually expressed by tho following signs degrees 

 ("), minute ('), seconds ("), thirds ("') ; 



As a general guide to us in estimating approximately tho 

 oa of tho stars, it will bo useful to remember that tho 

 a|>p.m>ni <lmm> UT of the sun or moon is about half a degree, 

 \vhilu tin- cli-t nice between the Pointers is about six ' 



that between the polo and tho !'< inter nearer to it (l)ubhe) 

 is about twenty-four degrees. By moans of a can-fully ^nula- 

 ated semicircle, we can easily measure any might, .< 

 tin- number of degrees it contains. 



Wo will not at present pursue our 

 study of the constellations, but as 

 soon as wo have completed our pene- 

 ral iden of 1 lio movements of the stars 

 we will deal more particularly with 

 those that are intimately associated 

 with us ;is members of our system, 

 and then return to consider the more 

 remote stars. 



As we continue to survey the 

 heavens for several evenings, we shall 

 soon discover that the stars remain in 

 the same relative position with re- 

 gard to one another. Just after 

 the new moon, before its light is 

 bright enough to obscure the light 

 of the stars around it, we shall 

 be able to observe its place among 

 them. Let us carefully note this, and 

 again examine tho spot on the follow- 

 ing evening. Wo shall now find that 

 the moon seems to have been lefb 

 behind by the stars, and instead of 

 appearing in tho same position as 

 before, it is some twelve or thirteen 

 degrees distant, and thus wo learn 

 that tho moon has a motion indepen- 

 dent of the rest of the stars. 



On further observation, too, we 

 shall detect one or two bright stars 

 which in a similar way change their 

 position, and hence are called planets, 

 or wanderers (for such is the meaning 

 of the word "planet"). Jupiter is 

 the most conspicuous of these, and 

 Venus sometimes known as the 

 Morning Star, and sometimes as the Evening Star, according to 

 the time when it is visible is another of them. These planets 

 appear so bright on account of their comparative nearness to 

 us ; they are, however, very different from the fixed stars, as 

 they do not shine by their own light, and are greatly inferior to 

 them in point of size. 



There is one other fact with regard to tho general apponranco 

 of tho sky which the student can likewise verify for himself. 

 Having fixed upon any bright star, lot him observe carefully 

 on any ovening the exact time of its passing the meridian, or of 

 its disappearance behind some conspicuous object. Observe 

 it again on the following evening, and again after the lapse of a 

 few more days, and it will at once be found that the star is a 

 little earlier every day in arriving at the place. Thus, if it bo 

 on the meridian at nine o'clock one day, it will be there about 

 four minutes before nine on tho next day, and so on. 



It is owing to this that we see different constellations at 

 different seasons of the year. Many of those which shine 

 brightly on a winter's night are above the horizon in the sum- 

 mer during tho daytime, and hence are invisible. In this way 

 wo KCO by far the larger portion of the stars at some time or 

 other of tho year ; but just as those stars within about fifty 

 degrees of tho north pole never set to us, so those within a 



himilur dintanoo of the Booth pole never rise at all ia or la*. 



Thu may eaaily be understood If the student possesses* trlrr 



tiul globe, lie ha* only to elevate UM north pole a* man; 

 degree* above the horizon hi* plaoe of obiaumtfon U north 

 of the oqoator, and then, M bo turns the globe OB its axis, be 

 will eee that the oiruompolar stars (M thaw round the north 

 polo are called) are constantly above the horizon, while as be 

 loolu more towarus the aouth j-olf, many only joat rue fora 

 hhort time and thun act again, and thoM still nearer UM pole 

 will never appear above the horizou. 



Among the moiit brilliant of the constellations tin* bidder 

 from ua ia the Southern Cross, and when traveller* are going 

 southward, the first appearance of this oonsteUatkm is generally 

 anxiously awaited. Aa the observer approaches the tropic*, the 

 pole star seems to sink lower and lower in the sky, and the 

 number of atara which never set become less and less, till when 

 he roaches the equator the pole is in the horizon, and oU the 

 start are seen ruing in the east, remaining visible exactly twelve 

 hours, and then setting in the 

 western horizon. They all appear 

 likewise to travel in perfectly 

 straight lines inatead of in corvee 

 as they do in other latitudes, and 

 hence the general appearance of the 

 sky ia very different from that seen 

 in England. 



By placing the artificial globe so 

 that its axis is horizontal, and its 

 pole in the horizon, wo iihall obtain 

 a representation of these pheno- 

 mena. 



If now wo could transfer ourselves 

 to the poles, the whole scene would 

 again vary. This has not yet been 

 actually done, but some Arctic tra- 

 vellers have penetrated very nearly 

 to the north pole, so that the move- 

 ments of the stars as seen by them 

 were almost exactly as we are aboot 

 to describe. 



No stars are now seen to rise or 

 set, bat all travel in circular paths 

 parallel to the horizon around the 

 polo star, which appears directly 

 overhead. Hence it is clear that all 

 the stars which are seen at any one 

 time remain constantly visible, while 

 one-half of the entire sky is con- 

 stantly hidden from their view. 



In a similar way, the changes of 

 day and night, of such great import- 

 ance to us, are unknown at the poles. 



'*' At tho commencement of their sum- 



mer tho sun is seen at first only partly 



elevated above the horizon, but travelling round to all parts of 

 the sky in the twenty-four hours, while at the same time his 

 altitude ia slowly increasing; and thus he remains constantly 

 visible for the space of six months, and then, for the remainder 

 of tho year, he never rises above the horizon. The year, there- 

 fore, consists of but a single day and night. The long night is 

 however, greatly relieved by twilight, which continues about two 

 months after the disappearance of tho sun, and is seen a similar 

 period before his rising. The Aurora Borealis or Northern 

 Lights, likewise, is soon in great brilliancy. 



The whole appearance of the Arctic sky is thus seen to bo 

 altogether different from that of ours. All these varied pheno- 

 mena, however, will bo found to admit of one simple explana- 

 tion. 



When wo have thns been gazing on the stars and their cease- 

 less motions, many questions come crowding into the mind about 

 their distances and sizes, the objects they serve, and the lawn 

 they obey. And then our thoughts go farther still as we 

 attempt to inquire what they are, and whether they, like oar 

 world, are inhabited. To some of these questions Astronomy 

 furnishes the answers ; and as to the rest, though it can give 

 no direct information, it furnishes as with a number of facts on 

 which we can base our speculations. 



