280 



THE POPULAR EDUCATOE. 



night seat himself at a window commanding an extensive view 

 of the heavens ; or, better still, let him go out in some place 

 where his view of the sky is as extensive as possible, and watch 

 for a short time the movements of the stars. If the night be 

 dark and clear, comparatively few will at first be seen, as the 

 pupil of the eye is contracted by the bright light of the room 

 which has just been left. In a few minutes, however, the eye 

 becomes accustomed to the light, and then the whole arch of 

 ueaven is seen to be thickly studded with stars. These differ 

 very greatly in brightness and size, so that he will soon be able 

 to fix on a few of the more conspicuous, and turn his main 

 attention to them. 



A compass should now be referred to, so as to ascertain the true 

 north and south points, and an imaginary curve passing vertically 

 overhead should be traced across the sky between these points. 

 This line is called the meridian ; and it will aid the student at first 

 if some prominent objects, as, for instance, trees or buildings, can 

 be fixed on to indicate permanently its position. Failing these, 

 some poles may be placed in the ground. In observatories, one 

 telescope is usually mounted on its axis in such a way that it can 

 only be directed to parts of the sky bordering upon this line, and 

 this is then known as the transit instrument. Its mode of con- 

 struction and uses will be fully explained by-aud-by. 



If now the position of any bright star be noticed, as may be 

 done by watching it against some fixed object, like the corner 

 of a house or the trunk of a tree, we shall soon find that it 

 appears to be in motion ; and further observation will show 

 that nearly all the stars appear to be similarly in motion, 

 though the rates at which they travel seem to vary slightly. 



Let us now face towards the south, and we shall soon see 

 that the stars on our left hand that is, towards the east are 

 rising higher and higher above the horizon; and if we could 

 map out their courses, or imagine them to leave threads of light 

 behind them, we should see that all these tracks would be arcs 

 of circles, and would be parallel to one another. 



These stars rise higher and higher till they come to the 

 meridian, and hero they are at their greatest elevation above 

 the horizon. They then commence to descend towards the west, 

 and it will be found that exactly the same time elapses between 

 the rising of any star and its coming to the meridian that there 

 is between this period and its sotting in the west. 



The point in the path of a star or planet on any given day 

 which is most elevated above the horizon is called its culminat- 

 ing point, and this point is always on the meridian. Hence any 

 of the heavenly bodies is said to culminate when it comes to 

 the meridian of any place. The term meridian signifies mid- 

 day, and the line is so called because, when the sun attains its 

 greatest altitude and crosses the meridian of any place, it is 

 mid-day there. 



If now we look quite to the south, we shall find that the 

 stars there only describe very small arcs, rising but a little way 

 above the horizon, and setting again in a very short time not 

 far from the same point, the highest altitude attained at any 

 time not being more than a few degrees. 



Now let us turn half round, so as to face the north instead 

 of the south, and, as before, observe the stars. We shall soon 

 be struck with the difference in the phenomena exhibited. We 

 shall now see that some of the stars never set, but describe 

 small circles, crossing the meridian twice in the course of the 

 twenty-four hours. We cannot, however, trace them completely 

 round their paths, as during a part of the time they are hidden 

 from the naked eye by the brilliancy of the sun's light. Even 

 by day, however, they may be seen with the aid of a good tele- 

 scope, if the means are possessed of directing it to them. It is 

 said, too, that at the bottom of a well or mine any bright stars 

 which happen to be vertically over the mouth may be seen, and 

 some have even seen stars during the day by looking up a 

 chimney. In either case, the rays of the sun are to a great 

 extent cut off by the walls or sides, and thus the faint light of 

 the star reaches the eye. It is, of course, only the brighter 

 stars that can be seen in this way, and as the number of stars 

 of the first and second magnitudes visible at any one time does 

 not exceed fifty, it will easily be understood that it will only be 

 on rare occasions that these effects will be witnessed. 



If now we look to a point on the meridian situated about 

 fifty-one degrees above the horizon, or rather more than half- 

 way from the horizon to the zenith, as the point directly over 

 head ia called, we shall find a star which appears not to move 



at all, but to remain constantly fixed in the same place, while 

 all the others revolve around it. This star is called the pole 

 star, and is well known, for before the discovery of the mari- 

 ner's compass it was used by sailors as their guide, being situated 

 due north. Very frequently, however, cloudy or duJ". vreather 

 would hide this star, sometimes for many days together, and 

 hence they were unable to go far out of sight of land, and 

 consequently navigation was but little practised in those days. 



If the student does not know this star, it is important for 

 him to find it at once, as it will be of great assistance to him in 

 learning the names and positions of others. The difficulty 

 which at first sight strikes us of learning the names of the 

 constellations soon disappears if we become familiar with a few 

 of the brighter ones, as by referring to them we shall soon be 

 able to identify the rest. Further on in the course of these 

 lessons we shall give illustrations of the position of the stars in 

 the most important constellations. It will, however, be a great 

 assistance to procure a complete set of maps of the stars, or, 

 better still, a celestial globe ; and a few hours' observation with 

 the aid of either of these will soon enable us to find any star, 

 or turn our attention to any part of the heavens which we may 

 desire. 



The constellation of the Great Bear (Ursa Major) or, as it is 

 sometimes called, Charles' Wain, or the Plough is well known 

 to most, it being a very conspicuous one, and one of those 

 which never set in this latitude. There are a considerable 

 number of stars in this constellation, but seven of them are 

 especially bright, and are arranged as shown in the lower part 

 of the accompanying figure. Four of them seem to form an 

 irregular square, while the other three, situated in the tail of 

 the Bear, are arranged in a curved lino going from one of the 

 corners of the square. 



Careful examination on a clear night will show that the 

 middle star of the tail is in reality double, consisting of two 

 stars so close together as apparently almost to touch one 

 another. They are called respectively Mizar and Alcor. A 

 telescope reveals a similar fact with regard to the first star in 

 the tail. We shall find as we further examine the sky many 

 of these double stars, and a telescope often showa them to be 

 of different colours, so that they are very beautiful objects. 



The two stars in the quadrangle which are farthest from the 

 tail are called " the Pointers," because, if a straight line be 

 drawn on a map so as to join them, and then be prolonged to 

 about five times the length, it will almost pass through the 

 Pole Star, which is the star at the tip of the tail of the Little 

 Bear (Ursa Minor). This constellation, which is shown in the 

 upper part of the figure, is almost exactly the same shape as 

 the one we have described, but it is turned in the opposite 

 direction, and the stars in it are much fainter, the pole star 

 being the brightest of them all. 



We spoke of the pole star as remaining at rest ; this is not, 

 however, perfectly correct, as it is not situated exactly at the 

 pole, but about one and a-half degrees from it, and hence it 

 appears to describe a circle of about three degrees in diameter. 

 This, however, is so small that it is only by the use of good 

 instruments that we can ascertain the fact, and in ordinary use 

 we may look upon the star as indicating the place of the pole 

 or imaginary axis round which the whole starry concave appears 

 to revolve. 



As we shall have frequent occasion in our lessons to speak of 

 degrees, it is as well for us to clearly understand at once what 

 we mean by a degree, and the mode in which we may measure 

 it. It is clearly necessary for us to have some means of 

 measuring the apparent distances of the heavenly bodies from 

 one another, and this can only be done by measuring the angle 

 which imaginary lines drawn from them to our eyes subtend. 

 If we think a moment, we shall see that it ia in the same way 

 that we form our estimate of the dimensions of ordinary objects 

 around us, and hence, when we bring them nearer to the eya 

 they appear larger, because the rays drawn from their extremes 

 to the eye contain a larger angle. Now, we want some means 

 of measuring and expressing in words the angle thus contained, 

 and this we do by means of degrees and fractions of a degree. 



A degree, then, is the 360th part of a circle i.e., if we draw a 

 large circle on paper, and divide its circumference into 360 equal 

 parts, and then draw straight lines from these divisions to tb . 

 centre of the circle, the angle contained between any two adja- 

 cent lines will be just one degree. On any circle we can draw 



