Слике страница
PDF
ePub

represents the four stars, and e 2 B the other

three.

Charles. What is the star p?

Tutor. That presents the polar star to which you just now alluded; and you observe, that if a line were drawn through the stars b, and a, and produced far enough, it would nearly touch it.

James. Let me look in the heavens for it by this guide. There it is, I suppose; it shines with a steady, and rather dead kind of light, and it appears to me, that it would be a little to the right of the line passing through the stars b and a.

Tutor. It would and these stars are generally known by the name of the pointers, because they point to p the north pole, which is situated a little more than two degrees from the star P.

Charles. Is that star always in the same part of the heavens ?

Tutor. It may be considered as uniformly maintaining its position, while the other stars seem to move round it as a centre. We shall have occasion to refer to this star again;

at present, I have directed your attention to it, as a proper method of finding the Cardinal points by star-light.

James. Yes, I understand now, that if I look to the north, by standing with my face to that star, the south is at my back, on my right hand is the east, and the west on my left.

Tutor. This is one important step in our astronomical studies; but we can make use of these stars as a kind of standard, in order to discover the names and positions of others in the heavens.

Charles. In what way must we proceed in this business?

Tutor. I will give you an example or two: conceive a line drawn from the star z, leaving в a little to the left, and it will pass through that very brilliant star A near the

horizon towards the west.

fames. I see the star, but how am I to know its name?

Tutor. Look on the celestial globe for the star z, and suppose the line drawn on the globe, as we conceived it done in the

CONVERSATION XXIV.

Of the Fixed Stars, and Ecliptic.

TUTOR.

I dare say that you will have no difficulty in finding the north polar star as soon as we go into the open air. James. I shall at once know where to look for that and the other stars which you pointed out last night, if they have not changed their places.

Tutor. They always keep the same position, with respect to each other, though their situation, with regard to the heavens, will be different at different seasons of the year, and in different hours of the night. Let us go into the garden.

Charles. The stars are all in the same place as we left them last evening. Now,

sir, if we conceive a straight line drawn through the two stars in the plough, which, in your figure (Fig. 1.) are marked d and g, and to extend a good way down, it will pass, or nearly pass through a very bright star, though not so bright as Arcturus or Capella, what is that called?

Tutor. It is a star of the second magnitude, and if you refer to the celestial globe, in the same way as you were instructed last night, you will find it is called Regulus, or Cor Leonis, the Lion's heart. By this method you may quickly discover the names of all the principal stars, and afterwards with a little patience, you will easily distinguish the others, which are less conspicuous.

Charles. But they have not all names; how are they specified?

Tutor. If you look on the globe, you will observe, that they are distinguished by the different letters of the Greek alphabet; and in those constellations, in which there are stars of different apparent magnitudes, the largest is a alpha, the next in size ẞ beta,

the third y gamma, the fourth ♪ delta, and

so on.

James. Is there any particular reason for this?

Tutor. The adoption of the characters of the Greek alphabet, rather than any other, was perfectly arbitrary; it is, however, of great importance, that the same characters should be used in general by astronomers of all countries, for by this means the science is in possession of a sort of universal language?

Charles. Will you explain how this is? Tutor. Suppose an astrónomer in North America, Asia, or any other part of the earth, observe a comet in that part of the heavens were the constellation of the plough is situated, and he wishes to describe it to his friend in Great Britain, in order that he may know, whether it was seen by the inhabitants of this island. For this pur pose, he has only to mention the time when he discovered it; its position, as nearest to some one of the stars, calling it by the Greek letter by which it is designated ; and

« ПретходнаНастави »