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24. As a further aid in finding particular stars, and especially in determining their number, and detecting changes, should any occur, catalogues of the stars have been constructed, one of which is over two thousand years old. Several of the principal stars have specific names, like the planets, as Sirius, Aldebaran, Regulus, &c.
25. The stars are still further distinguished, as single, double, triple, multiple, binary, variable, new, and nebulous.
A single star is one that appears as a unit under the most powerful telescopes. Double, triple, and multiple stars, are those that appear single to the naked eye, but by the aid of telescopes are found to consist of two or more stars. Binary stars are double stars revolving around each other, often called Binary Systems. Variable stars are those that are found to undergo certain fluctuations in their brightness, sometimes becoming quite invisible. In most cases these changes are periodical and regular, on which account they are called Periodical stars. New stars are those that suddenly blaze forth in some portion of the heavens previously void. Nebulous stars are those which are surrounded by a faint nebula, or halo of light or mist.
26. A cluster of stars is an assemblage or group, thrown promiscuously together, like the Pleiades and Hyades in Taurus, and the Bee Hive in Cancer. A Nebula is a cluster so remote as to appear only like a faint cloud or haze of light. Resolvable Nebula, are those that can be resolved into distinct stars by the aid of a telescope. Irresolvable Nebula are those that have not
24. What further aid? Age? Names of stars? 25. Stars, how further distinguished? Single stars? Double, &c.? Binary? What other name? Variable stars? What other name and why? New stars? Nebulous? 26. What are clusters? Nebulæ? Annular? Planetary?
Resolvable Nebula? Irresolvable?
as yet been thus resolved. Annular Nebula are those that have the form of an annulus or ring. Planetary Nebula are those that resemble planets in form, and in the sharpness of their outline. Stellar Nebula are those with a star in the centre, the same as nebulous stars, already described (25).
A more detailed account of the double stars, clusters and nebulæ, will be given after the student has become somewhat familiar with the constellations.
27. We may now imagine the pupil ready to begin the study of the visible heavens. The first thing of importance is to fix upon the proper starting point. This, on many accounts, would seem to be the North Polar Star. Its position is apparently the same every hour of the night throughout the year, while the other stars are continually moving. Many of the stars also in that region of the skies never set, so that when the sky is clear, they may be seen at any hour of the night. They revolve about the pole in small circles, and never disappear below the horizon.
On this account they are said to be within the circle of perpetual apparition. On the other hand, the identity of the North Polar Star, strange as it may appear, is not so easily determined by those who are just entering upon this study, as that of some others. For this reason, the point directly overhead, called the zenith, is preferable, since upon this point every one can fix with certainty in whatever latitude he may be. It will be alike to all the central point of the visible heavens, and to it the pupil will learn imperceptibly to refer the bearing, motion, and distances of the heavenly bodies.
That meridional point in each map, whose declination corresponds with the latitude of the place of observation, represents the zenith of the heavens at that place; and those constellations of stars which occupy this position on the maps, will be seen directly overhead at 9 o'clock in the evening of the day through which the meridian passes. Thus in Georgia, for instance, the starting point should be those stars which are situated in this meridian near the 33d degree of north declination, while in New England it should be those which are situated in it near the 42d degree.
28. We might, however, begin with the stars near either of the meridians represented on the maps, the only rule of selection being to commence at that which approaches nearest to being overhead at the time required. We have chosen for our starting point in this work that meridian which passes through the vernal equinox at the first point of Aries, not only because it is the meridian from which the distances of all the heavenly bodies are measured; but especially because the student will thus be enabled to observe and compare the progressive motion of the constellations according to the order in which they are always arranged in catalogues, and also to mark the constellations of the Zodiac passing overhead as they rise one after another in their order, and to trace among them the orbits of the Earth and of the other planets.
27. What first important in commencing study of the heavens? What star would seem best starting point? Why? Why not the best? What point preferable, and why? Illustration from map. 28. With what stars might we begin? What meridian thosen by the author? Why?
CONSTELLATIONS ON THE MERIDIAN IN NOVEMBER.
29. If we look directly overhead at 10 o'clock, on the 10th of November, we shall see the constellation celebrated in fable by the name of ANDROMEDA. It is represented on the map by the figure of a woman having her arms extended, and chained by her wrists to a rock. It is bounded N. by Cassiopeia, E. by Perseus and the head of Medusa, and S. by the Triangles and the Northern Fish. It is situated between 20° and 50° of N. declination. Its mean right ascension is nearly 15°; or one hour E. of the equinoctial colure.
30. It consists of 66 visible stars, of which three are of the 2d magnitude, and two of the 3d; most of the rest are small. The stars directly in the zenith are too small to be seen in the presence of the moon, but the bright star Almaack (y), of the 2d magnitude, in the left foot, may be seen 13° due E., and Merach (B), of the same magnitude, in the girdle 7° south of the zenith. This star is then nearly on the meridian, and with two others N.W. of it forms the girdle.
The three stars forming the girdle are of the 2d, 3d, and 4th magnitude, situated in a row, 3° and 4° apart, and are called Merach, Mu, and Nu.
31. If a straight line, connecting Almaack with Merach, be
*As the eastward motion of the earth in her orbit causes the sun to pass eastward annually around the heavens, and the constellations to rise earlier and earlier (19), the student will find it necessary to proceed eastward around the heavens, in studying the constellations. And as the right hand of the map is west, and the left hand east, we begin with the equinoctial colure, map II., and proceed to the left in the order in which the constellations successively arise.
29. What constellation? Maps, and why? (Note.) How Andromeda represented? Boundaries? Situation? Right ascension and declination? 30. Number of stars? Magnitude? Almaack? Merach? "Girdle ?" 31. Situation of Delta? Magnitude? How otherwise known? Alpheratz? Substance of note (fine print)?
produced south-westerly, 8° farther, it will reach to (d) Delta, a star of the 3d magnitude in the left breast. This star may be otherwise known by its forming a line, N. and S., with two smaller ones on either side of it; or, by its constituting, with two others, a very small triangle, S. of it.
Nearly in a line with Almaack, Merach and Delta, but curving a little to the N. 7° farther, is a lone star of the 2d magnitude, in the head, called Alpheratz (a). This is the N.E. corner of the great "Square of Pegasus," to be hereafter described.
It will be well to have the position of Alpheratz well fixed in the mind, because it is but one minute west of the great equinoctial colure, or first meridian of the heavens, and forms nearly a right line with Algenib, in the wing of Pegasus, 14° S. of it, and with Beta in Cassiopeia, 30° N. of it. If a line, connecting these three stars, be produced, it will terminate in the pole. These three guides, in connection with the North Polar Star, point out to astronomers the position of that great circle in the heavens from which the right ascension of all the heavenly bodies is measured.
32. The story of Andromeda, from which this constellation derives its name, is as follows: She was daughter of Cepheus, King of Ethiopia, by Cassiopeia. She was promised in marriage to Phineus, her uncle, when Neptune drowned the kingdom, and sent a sea monster to ravage the country, to appease the resentment which his favorite nymphs bore against Cassiopeia, because she had boasted herself fairer than Juno and the Nereides. The oracle of Jupiter Ammon was consulted, and nothing could pacify the anger of Neptune unless the beautiful Andromeda should be exposed to the sea monster. She was accordingly chained to a rock for this purpose, near Joppa (now Jaffa, in Syria), and at the moment the monster was going to devour her, Perseus, who was then returning through the air from the conquest of the Gorgons, saw her, and was captivated by her beauty.
"Chained to a rock she stood; young Perseus stay'd
He promised to deliver her and destroy the monster if Cepheus would give her to him in marriage. Cepheus consented, and Perseus instantly changed the sea monster into a rock, by showing him Medusa's head, which was still reeking in his hand. The enraged Phineus opposed their nuptials, and a violent battle ensued, in which he, also, was turned into a stone, by the petrifying influence of the Gorgen's head.
The morals, maxims, and historical events of the ancients, were usually communicated in fable or allegory. The fable of Andromeda and the sea monster might mean that she was courted by some monster of a sea-captain, who attempted to carry her away, but was prevented by another more gallant and successful rival.
33. Under the head of Telescopic Objects, will be included clusters and nebula that are visible to the naked eye, as well as the principal objects of interest that are strictly telescopic. In describing the location of these objects, R. A. will denote Right Ascension; and Dec., Declination. The initials N. and S. will indicate whether the declination is North or South of the equinoctial.
In describing the location of the telescopic object, the R. A. will be given in time; viz., in hours, minutes, and seconds, instead of degrees, minutes, and seconds; each hour answering to 15°. The hour circles are distinctly drawn on all the maps, the first being 15° east of the equinoctial colure (Map II.), and so on eastward to the same point again. The hours will be seen marked just under the equinoctial, which is marked off into degrees, each of which answers to four minutes of time. The student will soon find it much more convenient to reckon R. A. by hours, on the maps, than by degrees, &c.
32. HISTORY.-What may it have meant?
33. What included among Telescopic Objects? What meant by R. A.? Dec.? N. and S.? How R. A. laid down? How on map? What mode of describing components of double stars? Of a Andromeda ? Of discrepancies between R. A. given, and location of stars on the maps? How is R. A. given in locating objects? Why? How are hours marked on the maps? The minutes?
34. In consequence of the perpetual recession of the equinoxes westward, the R. A. of objects is constantly increased by about 50" per year. It is vain, therefore, to attempt to give R. A. for the time when a book will be used; or to construct maps that will show objects in their true place, for different years to come. The necessary allowance must be made in all cases; so that the R. A. for one epoch is about as good as another. The R. A. here given is from Smyth's Celestial Cycle, epoch Jan. 1, 1840. Maps should be re-engraved every fifty years, but for all shorter periods allowance can be made by the student. As the maps accompanying this work were drawn and engraved in 1835, their present R. A. (1854) is about 17' or 4m. of time east of their places on the maps.
35. The order in which the telescopic objects will be arranged is first the double stars; secondly, clusters; and lastly the nebulæ. The double stars will be classed according to their order in the respective constellations; i.e., a first, ẞ next, &c. Thus, as the largest objects are first named, the student can begin with those easiest found, and requiring the least telescopic power; and proceed from the easier to those more difficult. The same plan is generally pursued with the clusters and nebulæ.
TELESCOPIC OBJECTS IN ANDROMEDA.
1. α ANDROMEDA (Alpheratz)-A star with a minute companion, R. A. 0h. 0m. 08s.: Dec., N. 28° 12′ 05". A. 1, bright white; B. 11, purplish. On the map it is west of the equinoctial, the map having been engraved some twenty years; but the equinox having constantly receded westward, had passed Alpheratz before 1840, some 8'. Similar discrepancies between the R. A. given and the location of different stars on the map, are due to the same cause.
2. ANDROMEDA (Merach)-A bright star with a distant telescopic companion, R. A. 1h. 00m. 47s.; Dec., N. 84° 46' 08". A. 2, fine yellow; B. 12, pale blue, with several small stars in the field.
3. Y ANDROMEDA (Almuack)-A SPLENDID DOUBLE STAR on the right foot, R. A. 1h. 54m. 06s; Dec. N. 41° 33' 06". A. 3%, orange color; B. 5%, emerald green. Found by a line from to B, and about twice as far beyond. (Map VIII., Fig. 1.)
ANDROMEDE-A bright star on the right breast, with a distant telescopic companion, R. A. Oh. 30m. 47s.; Dec., N. 29° 59' 01". A. 3, orange; B. 11, dusky; with the small stars in the southern part of the field.
5. K ANDROMEDE-A wide, but delicate TRIPLE STAR, in the northern hand; midway between Pegasi and a Cassiopeia; or about 18° from each; R. A. 23h. 32m. 33s; Dec., N. 43° 27' 0". A. 5, brilliant white; B. 14, dusky; C. 12, ash-colored.
6. AN ELONGATED NEBULA on the lady's right foot, R. A, 2h. 12m. 35s.; Dec., N. 41° 36". It was discovered by Miss Caroline Herschell, in 1783. Sir William Herschell described it as having "a black division or chink in the middle." He regarded it as a flat ring of enormous dimensions, seen very obliquely. Captain Smyth says: "In my telescope it is certainly brighter at the edges than along the central part." See map VIII., Fig. 21. 7. About 2° from Nu at the north-western extremity of the girdle, R. A. 00° 34m. 05s., N. Dec., 40° 23' 06", is a remarkable nebula of very minute stars, and the only one of the kind which is ever visible to the naked eye. It resembles two cones of light, joined at their base, about 3° in length, and 4° in breadth. It was known as far back as A.D. 905, is of an oval shape, and is described by Smyth as "an overpowering nebula, with a companion about 25' in the south vertical." Sir William Herschell considered this the nearest of all the great nebulæ, and yet so remote that it would require 6,000 years for light to pass from it to our system, though flying at the rate of 190,000 miles per second! Fig. 22, map VIII., is a representation of this object.
PISCES (THE FISHES).—MAP V.
36. This constellation is now the first in order of the twelve constellations of the Zodiac, and is usually represented by two fishes tied a considerable distance apart, at the extremities of a long undulating cord, or ribbon. It occupies a large triangular space
34. What said of the change of R. A. of objects? Cause? Epoch of R. A. given in book? Of that marked on maps? Allowance to be made in finding objects by maps? 85. Order in which objects are presented? Advantage of this arrangement?
What clusters or nebulse?
TELESCOPIC OBJECTS.-What double stars? a? B? y? Shown on map, or not?
36. Pisces? Where situated? What now called?