been determined, that if we put the light of a star, of the CHAP. IV. average 1st magnitude, 100, we shall have:

1st magnitude = 100

4th magnitude = 6

On this scale, Sir William Herschel placed the brightness of

Sirius at 320.

Ancient astronomy has come down to us much tarnished with superstition, and heathen mythology. Every constellation bears the name of some pagan deity, and is associated with some absurd and ridiculous fable; yet, strange as it may appear, these masses of rubbish and ignorance—these clouds and fogs, intercepting the true light of knowledge, are still not only retained, but cherished, in many modern works, and dignified with the name of astronomy.

Ancient names must

Merely as names, either to constellations or to individual stars, we shall make no objections; and it would be useless, be conti. if we did; for names long known, will be retained, however nued. improper or objectionable; hence, when we speak of Oricn, the Little Dog, or the Great Bear, it must not be understood that we have any great respect for mythology.

It is not our purpose now to describe the starry heavensthe to point out the variable, double, and multiple stars Milky Way and nebula; these will receive special attention in some future chapter: at present, our only aim is to point out the method of obtaining a knowledge of the mere appearance of the sky, to the common observer, which may be called the geography of the heavens.

To give a person an idea of locality, on the earth, we refer to points and places supposed to be known. Thus, when we say that a certain town is 15 miles north-west of Boston, a ship is 100 miles east of the Cape of Good Hope, or a certain mountain 10 miles north of Calcutta, we have a pretty definite idea of the localities of the town, the ship, and the mountain, on the face of the earth, provided we have a clear idea of the face of the earth, and know the position of Boston, the Cape of Good Hope, and Calcutta.

So it is with the geography of the heavens; the apparent

Stars about the pole.

CHAP. IV. surface of the whole heavens must be in the mind, and then the localities of certain bright stars must be known, as landmarks, like Boston, the Cape of Good Hope, and Calcutta. We shall now make some effort to point out these landmarks. The North Star is the first, and most important to be recognized; and it can always be known to an observer, in any northern latitude, from its stationary appearance and åltitude, equal to the latitude of the observer. At the distance of about 32 degrees from the pole, are seven bright stars, between the 1st and 2d magnitudes, forming a figure resembling a dipper, four of them forming the cup, and three the handle. The two forming the sides of the cup, opposite to the handle, are always in a line with the North Star; and are therefore called pointers: they always point to the North Star. The line joining the equinoxes, or the first meridian of right ascension, runs from the pole, between the other two stars forming the cup. The first star in the handle, nearest the cup, is called Alioth, the next Mizar, near which is a small star, of the 4th magnitude; the last one is Benetnasch. The stars in the handle are said to be in the tail of the Great Bear.

Imaginary

lines

star to star.

About four degrees from the pole star, is a star of the 3d magnitude, Ursa Minoris. A line drawn through the pole (not pole star) and this star, will pass through, or very near, the poles of the ecliptic and the tropics. A small constellation, near the pole, is called Ursa Minor, or the Little Bear. An irregular semicircle of bright stars, between the dipper and the pole, is called the Serpent.

If a line be drawn from Ursa Minoris, through the pole from star, and continued about 45 degrees, it will strike a very beautiful star, of the 1st magnitude, called Capella. Within five degrees of Capella are three stars, of about the 4th magnitude, forming a very exact isosceles triangle, the vertical angle about 28 degrees. A line drawn from Alioth, through the pole star, and continued about the same distance on the other side, passes through a cluster of stars called Cassiopia in her chair. The principal star in Cassiopea, with the pole star and Capella, form an isosceles triangle, Capella at the

vertex.

(46.) More attention has been paid to the constellations CHAP. IV. along the equator and ecliptic, than to others in remoter Ecliptic regions of the heavens, because the sun, moon, and planets, defined. traverse through them. The ecliptic is the sun's apparent annual path among the stars (so called because all eclipses, of both sun and moon, can take place only when the moon is either in or near this line).

the zodiac.

Eight degrees on each side of the ecliptic is called the Signs of zodiac; and this space the ancients divided into 12 equal parts (to correspond with the 12 months of the year), and each part (30°) is called a sign—and the whole, the signs of the zodiac. These divisions are useless; and, of late years, astronomers have laid them aside; yet custom and superstition will long demand a place for them in the common almanacs.

The signs of the zodiac, with their symbolic characters, are as follows: Aries Y, Taurus 8, Gemini п, Cancer, Leo, Virgo my, Libra, Scorpio m, Sagittarius &, Capricornus, Aquarius, Pisces .

Owing to the precession of the equinoxes, these signs do not correspond with the constellations, as originally placed : the variation is now about 30 degrees; the stars remain in their places; and the first meridian, or first point of Aries, has drawn back, which has given to the stars the appearance of moving forward.

stars.

Beginning with the first point of Aries as it now stands, Method of no prominent star is near it; and, going along the ecliptic to tracing the the eastward, there is nothing to arrest special attention, until we come to the Pleiades, or Seven Stars, though only six are visible to the naked eye. This little cluster is so well known, and so remarkable, that it needs no description. Southeast of the Seven Stars, at the distance of about 18 degrees, is a remarkable cluster of stars, said to be in the Bull's Head; the largest star in this cluster is of the 1st magnitude, of a red color, called Aldebaran. It is one of the eight stars selected as points from which to compute the moon's distance, for the assistance of navigators.

This cluster resembles an A when east of the meridian, and

D*

CHAP. IV.

The con

are above the

a V when west of it. The Seven Stars, Aldebaran, and Capella, form a triangle very nearly isosceles - Capella at the vertex. A line drawn from the Seven Stars, a little to the west of Aldebaran, will strike the most remarkable constellation in the heavens, Orion (it is out of the zodiac, however): some call it the Ell and Yard. The figure is mainly distinguished by three stars, in one direction, within two degrees of each other; and two other stars, forming, with one of the three first mentioned, another line, at right angles with the first line.

The five stars, thus in lines, are of the 1st or 2d magnitude. A line from the Seven Stars, passing near Aldebaran and through Orion, will pass very near to Sirius, the most brilliant star in the heavens. The ecliptic passes about midway between the Seven Stars and Aldebaran, in nearly an eastern direction. Nearly due east from the northernmost and brightest star in Orion, and at the distance of about 25 degrees, is the star Procyon; a bright, lone star.

The northernmost star in Orion, with Sirius and Procyon, form an equilateral triangle.

Directly north of Procyon, at the distances of 25 and 30 stellations degrees, are two bright stars, Castor and Pollux. Castor is horizon, and the most northern. Pollux is one of the eight lunar stars. visible every Thus we might run over that portion of the heavens which is ring the win-ever visible to us, and by this method every student of astronomy can render himself familiar with the aspect of the sky; but it is not sufficiently definite and scientific to satisfy a mathematical mind.

evening du

ter season.

General

and indefi

(47.) The only scientific method of defining the position of a place on the earth, is to mention its latitude and longitude; and this method fully defines any and every place, however unimportant and unfrequented it may be so in astronomy, the only scientific methods of defining the position of a star, is to mention its latitude and longitude, or, more conveniently, its right ascension and declination.

It is not sufficient to tell the navigator that a coast makes nite descrip- off in such a direction from a certain point, and that it is so tisfactory. far to a certain cape; and, from one cape to another, it is

tions not sa

every

stitutes a definite de.

about 10 miles south-west- he would place very little reli- CHAP. JV. ance on any such directions. To secure his respect, and What con. command his confidence, the latitude and longitude of point, promontory, river, and harbor, along the coast, must be scription. given; and then he can shape his course to any point, or strike in upon it from the indefinite expanse of a pathless sea. So with an astronomer; while he understands and appreciates the rough and general descriptions, such as we have just given, he requires the certain description, comprised in right ascension and declination.

Accordingly, astronomers have given the right ascensions and declinations of every visible star in the heavens (and of very many that are invisible), and arranged them in tables, in the order of right ascension.

John Bay.

of reference.

There are far too many stars, for each to have a proper name; and, for the sake of reference, Mr. John Bayer, of er's method Augsburg, in Suabia, about the year 1603, proposed to denote the stars by the letters of the Greek and Roman alphabets; by placing the first Greek letter a to the principal star in the constellation, to the second in magnitude, to the third, and so on; and if the Greek alphabet shall become exhausted, then begin with the Roman, a, b, c, etc.

"Catalogues of particular stars, in sections of the heavens, Particular have been published by different astronomers, each author catalogues. numbering the individual stars embraced in his list, according to the places they respectively occupy in the catalogue." These references to particular catalogues are sometimes marked on celestial globes, thus: 79 H, meaning that the star is the 79th in Herschel's catalogue; 37 M, signifies the 37th number in the catalogue of Mayer, etc.

Among our tables will be found a catalogue of a hundred of the principal stars, inserted for the purpose of teaching a definite and scientific method of making a learner acquainted with the geography of the heavens.

To have a clear understanding of the method we are about to explain, we again consider that right ascension is reckoned from the equinox, eastward along the equator, from 0 h. to 24 hours. When the sun comes to the equator, in March, its