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THE UNICORN. This is a modern constellation, which was made out of the unformed stars of the ancients that lay scattered over a large space of the heavens between the two Dogs. It extends a considerable distance on each side of the equinoctial, and its centre is on the same meridian with Procyon.
It contains 31 small stars, of which the seven principal ones are of only the 4th magnitude. Three of these are situated in the head, 3° or 4° apart, forming a straight line N. E. and S. W. about 9° E. of Betelguese in Orion's shoulder, and about the same distance S. of Alhena in the foot of the Twins.
The remaining stars in this constellation are scattered over a large space, and being very small, are unworthy of particular notice.
HISTORY. THE MONOCEROS is a species of the Unicorn or Rhinoceros. It is about the size of a horse, with one white horn growing out of the middle of its forehead. It is said to exist in the wilds of Ethiopia, and to be very formidable.
Naturalists say that, when pursued by the hunters, it precipitates itself from the tops of the highest rocks, and pitches upon its horn, which sustains the whole force of its fall, so that it receives no damage thereby. Sparmann informs us, that the figure of the unicorn, described by some of the ancients, has been found delineated on the surface of the rock in Caffraria; and thence conjectures that such an animal, instead of being fabulous, as some suppose, did once actually exist in Africa. Lobo affirms that he has seen it.
The rhinoceros, which is akin to it, is found in Bengal, Siam, Cochin China, part of China Proper, and the isles of Java and Sumatra.
THE GREAT DOG. This interesting constellation is situated southward and eastward of Orion, and is universally known by the brilliance of its principal star, Sirius, which is apparently the largest and brightest in the heavens. It glows in the winter hemisphere with a lustre which is unequalled by any other star in the firmament.
Its distance from the earth, though computed at 20 millions of millions of miles, is supposed to be less than that of any other star: a distance, however, so great that a cannon ball, which flies at the rate of 19 miles a minute, would be two millions of years in passing over the mighty interval; while sound, moving at the rate of 13 miles a minute, would reach Sirius in little less than three millions of years.
What stars compose the constellation Monoceros? How is this constellation situated, and when is it on the meridian? What is the whole number of its stars? What Is the magnitude of its principal ones? Describe those in the head. Describe the poition and appearance of Canis Major. What is its appearance in the winter? What Is its distance from the earth computed to be, and how is it compared with that of the other stars? How long would it take a cannon-ball to pass over this distance In what time would sound reach Sirius from the earth?
It may be shown in the same manner, that a ray of light, which occupies only 8 minutes and 13 seconds in coming to us from the sun, which is at the rate of nearly two hundred thousand miles a second, would be 3 years and 82 days in passing through the vast space that lies between Sirius and the earth. Consequently, were it blotted from the heavens, its light would continue visible to us for a period of 3 years and 82 days after it had ceased to be.
If the nearest stars give such astonishing results, what shall we say of those which are situated a thousand times as far beyond these, as these are from us?
In the remote ages of the world, when every man was his own astronomer, the rising and setting of Sirius, or the Dogstar, as it is called, was watched with deep and various solicitude. The ancient Thebans, who first cultivated astronomy in Egypt, determined the length of the year by the number of its risings.) (Th The Egyptians watched its rising with mingled apprehensions of hope and fear; as it was ominous to them of agricultural prosperity or blighting drought It foretold to them the rising of the Nile, which they called Siris, and admonished them when to sow The Romans were accustomed yearly, to sacrifice a dog to Sirius to render him propitious in his influence upon their herds and fields. The eastern nations generally believed the rising of Sirius would be productive of great heat on the earth.
"Tuni steriles exurere Sirius agros: Ardebant herbæ, et victum seges ægra negabat."
"Parched was the grass, and blighted was the corn:
Accordingly, to that season of the year when Sirius rose with the sun and seemed to blend its own influence with the heat of that luminary, the ancients gave the name of Dogdays, (Dies Caniculares). At that remote period the Dogdays commenced on the 4th of August, or four days after the summer solstice, and lasted forty days or until the 14th of September. At present the Dog-days begin on the 3d of July, and continue to the 11th of August, being one day less than the ancients reckoned.
Hence, it is plain that the Dog-days of the moderns have no reference whatever to the rising of Sirius, or any other star, because the time of their rising is perpetually accelerated by the precession of the equinoxes: they have reference then only to the summer solstice which never changes its position in respect to the seasons.
How long is light in coming from Sirius to the earth? Suppose this star were now to be blotted from the heavens, how long before its twinkling would expire? How was the rising of Sirius regarded in the remote ages of the world? What use was made of it by the ancient Thebans? How did the Egyptians regard it, and for what reason? What did it foretel to them? What did the Romans offer in sacrifice to Sirius annually? Why? How was it regarded by the eastern nations generally? What season of the year did the ancients call Dog-days? When did these begin, and how long did they last? At present, when do they begin and end' Have our Dog-days any reference to the Dog-star?
The time of Sirius' rising varies with the latitude of the place, and in the same latitude, is sensibly changed alter a course of years, on account of the precession at the equinoxes. This enables us, to determine with approximate accuracy, the dates of many events of antiquity, which cannot be well determined by other records. We do not know, for instance, in what precise period of the world Hesiod flourished. Yet he tells us, in his Opera et Dies, lib. i. v. 185, that Arcturus in his time rose heliacally, 60 days after the winter solstice, which, then was in the 9th degree of Aquarius, or 390 beyond its present position. Now 39° 50"-2794 years since the time of Hesiod, which corresponds very nearly with history.
When a star rose at sun-setting, or set at sun-rising, it was called the Achroni cal rising or setting. When a planet or star appeared above the horizon just before the sun, in the morning, it was called the Heliacal rising of the star; and when it sunk below the horizon immediately after the sun, in the evening, it was called the Heliacal setting. According to Ptolemy, stars of the first magnitude are seen rising and setting when the sun is 12° below the horizon; stars of the 2d magnitude require the sun's depression to be 13°; stars of the 3d magnitude, 14°, and so on, allowing one degree for each magnitude. The rising and setting of the stars described in this way, since this mode of description often occurs in Hesiod, Virgil, Columella, Ovid, Pliny, &c. are called poetical rising and setting. They served to mark the times of religious ceremonies, the seasons allotted to the several departments of husbandry, and the overflowing c Nile
The student may be perplexed to understand how the Dog-star, which he seldom sees till mid-winter, should be associated with the most fervid heat of summer. This is explained by considering that this star, in summer, is over our heads in the daytime, and in the lower hemisphere at night. As "thick the floor of heaven is inlaid with patines of bright gold," by day, as by night; but on account of the superior splendour of the sun, we cannot see them.
Sirius is situated nearly S. of Alhena, in the feet of the Twins, and about as far S. of the equinoctial as Alhena is N. of it. It is about 100 E. of the Hare, and 26° S. of Be telguese in Orion, with which it forms a large equilateral triangle. It also forms a similar triangle with Phaet in the Dove, and Naos in the Ship. These two triangles being joined at their vertex in Sirius, present the figure of an enormous X, called by some, the ÉGYPTIAN X. Sirius is also pointed out by the direction of the Three Stars in the belt of Orion. Its distance from them is about 23°. It comes to the meridian at 9 o'clock on the 11th of February.
Mirzam, in the foot of the Dog, is a star of the 2d magnitude, 540 W. of Sirius. A little above, and 4° or 5° to the left, there are three stars of the 3d and 4th magnitudes, forming a triangular figure somewhat resembling a dog's head.
What is meant by the Achronical rising and setting of the stars? What, by their Heliacal rising and setting? By whom were the terms thus applied, and what were these risings and settings called? What did they serve? Explain how it is, that the Dog-star, which is seldom seen till mid-winter, should be associated with the most fervid heat of summer. Are there as many stars over our head in the daytime as in the night? Describe the situation of Sirius. What is its position with regard to Betelguese and Procyon, and in connexion with them what figure does it form? With what other stars does it form a similar triangle? What is the appearance of these two triangles taken together? How else is Sirius pointed out? Describe the position and magnitude of Mirzam. What stars mark the head of the Dog?
The brightest of them, on the left, is called Muliphen. It entirely disappeared in 1670, and was not seen again for more than 20 years. Since that time it has maintained a steady lustre.
Wesen is a star of between the 2d and 3d magnitudes, in the back, 11° S. S. E. of Sirius, with which, and Mirzam in the paw, it makes an elongated triangle. The two hinder feet are marked by Naos and Lambda, stars of the 3d and 4th magnitudes, situated about 3° apart, and 12° directly S. of the fore foot. This constellation contains 31 visible stars, including one of the 1st magnitude, four of the 2d, and two of the 3d; all of which are easily traced out by the aid of the map.
HISTORY.-Manilius, a Latin poet who flourished in the Augustan age, wrote an admirable poem, in five books, upon the fixed stars in which he thus speaks of this constellation:
"All others he excels; no fairer light
Ascends the skies, none sets so clear and bright."
But EUDOSIA best describes it :
"Next shines the Dog with sixty-four distinct;
His fierce mouth flames with dreaded Sirius;
According to some mythologists, this constellation represents one of Orion's hounds, which was placed in the sky, near this celebrated huntsman. Others say it received its name in honour of the dog given by Aurora to Cephalus, which surpassed in speed all the animals of his species. Cephalus, it is said attempted to prove this by running him against a fox, which, at that time, was thought to be the fleetest of all animals. After they had run together a long time without either of them obtaining the victory, it is said that Jupiter was so much gratified at the fleetness of the dog that he assigned him a place in the heavens.
But the name and form of this constellation are, no doudt, derived from the Egyptians, who, carefully watched its rising, and by it judged of the swelling of the Nile, which they called Siris, and, in their hieroglyphical manner of writing, since it was as it were the sentinel and watch of the year, represented it under the figure of a dog. They observed that when Sirius became visible in the east, just before the morning dawn, the overflowing of the Nile immediately followed. Thus it warned them, like a faithful dog, to escape from the region of the inundation.
DIRECTIONS FOR TRACING THE CONSTELLATIONS WHICH ARE ON THE MERIDIAN IN MARCH.
THE SHIP ARGO.-This constellation occupies a large space in the southern hemisphere, though but a small part of it can
Which is the brightest of these, and what remarkable circumstance in its history? How has it appeared since its return? Describe the situation and magnitude of Wesen? What stars mark the hinder feet? What is the number of visible stars in this constellation Describe the constellation Argo Navis?
be seen in the United States. It is situated S. E. of Canis Major, and may be known by the stars in the prow and deck of the ship.
If a straight line joining Betelguese and Sirius, be produced 18° to the southeast, it will point out Naos, a star of the 2d magnitude, in the rowlock of the ship. This star is in the S. E. corner of the Egyptian X., and of the large equilateral triangle made by itself with Sirius and the Dove. When on the meridian, it is seen from this latitude about 8° above the southern horizon. It comes to the meridian on the 3d of March, about half an hour after Procyon, and continues visible but a few hours.
Gamma, in the middle of the ship, is a star of the 2d magnitude, about 70 S. of Naos, and just skims above the southern horizon for a few minutes, and then sinks beneath it. The principal star in this constellation is called, after one of the pilots, Canopus; it is of the 1st magnitude, 36° nearly S. of Sirius, and comes to the meridian 17 minutes after it; but having about 53° of S. declination, it cannot be seen in the United States. The same is true of Miaplacidus, a star of the 1st magnitude in the oars of the ship, about 25° E. of Canopus, and 61° S. of Alphard, in the hear of Hydra.
An observer in the northern hemisphere, can see the stars as many degrees south of the equinoctial in the southern hemisphere, as his own latitude lacks of 90°, and no more.
Markeb, is a star of the 3d magnitude, in the prow of the ship, and may be seen from this latitude, 16° S. É. of Sirius, and about 10° E. of Wesen, in the back of the Dog. This star may be known by its forming a small triangle with two others of the same magnitude, situated a little above it, on the E., 30 and 4° apart.
This constellation contains 64 stars, of which, two are of the 1st magnitude, four of the 2d, and nine of the 3d. Most of these are too low down to be seen in the United States.
HISTORY.-This constellation is intended to perpetuate the memory of the famous ship which carried Jason and his 54 companions to Colchis, when they resolved upon the perilous expedition of recovering the golden fleece. The derivation of the word Argo has been often disputed. Some derive it from Argos, supposing that this was the name of the person who first proposed the expedi tion, and built the ship. Others maintain that it was built at Argos, whence its name. Cicero calls it Argo, because it carried Grecians, commonly called Argives. Diodorus derives the word from which signifies swift. Ptolemy says, but not truly, that Hercules built the ship and called it Argo, after a son of Jason, who bore the same name. This ship had fifty oars, and being thus propelled must have fallen far short of the bulk of the smallest ship craft used by
Where is it situated? Point out the situation of Naos, in the ship? When may it be seen in this latitude? When is it on the meridian? Describe the position and magnitude of Gamma. What are the situation and name of the principal star in this constellation? Why can it not be seen in the United States? Is any other considerable star in the ship similarly situated? Describe Markeb. How may this star be known? What is the number of visible stars in this constellation? What is the magnitude of its principal ones?