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Sir John Herschel considered this the most remarkable binary star known, and the only one that had completed a whole revolution since its discovery. Estimated period 432 years.
URSA MINOR (THE LESSER BEAR).-MAP VI.
189. This constellation, though not remarkable in its appear ance, and containing but few conspicuous stars, is, nevertheless, justly distinguished from all others for the peculiar advantage which its position in the heavens is well known to afford to nautical astronomy, and especially to navigation and surveying.
The stars in this group being situated near the celestial pole, appear to revolve about it, very slowly, and in circles so small as never to descend below the horizon. Hence Ursa Minor will be above or below, to the right or left of the pole star, according to the hour; as he makes the entire circuit from east to west every 24 hours.
190. In all ages of the world, this constellation has been more universally observed, and more carefully noticed than any other, on account of the importance which mankind early attached to the position of its principal star. This star, which is so near the true pole of the heavens, has from time immemorial been denominated the NORTH POLAR STAR. By the Greeks it is called Cynosyre; by the Romans, Cynosura, and by other nations, Alruccabah. In most modern treatises it bears the name of Polaris, or Alpha Polaris.
191 Polaris is of the 3d magnitude, or between the 2d and 3d, and situated a little more than a degree and a half from the true pole of the heavens, on that side of it which is toward Cassiopeia and opposite to Ursa Major. Its position is pointed out by the direction of the two Pointers, Merak and Dubhe, which lie in the square of Ursa Major. A line joining Beta Cassiopeia, which lies at the distance of 32° on one side, and Megrez, which lies at the same distance on the other, will pass through the polar star.
Of the Pole Star Capt. Smyth observes: At present it is only 1° 38' from the polar point, and by its northerly precession in declination will gradually approach to within 26′ 80* of it. This proximity to the actual pole will occur in A. D. 2095, but will not recur for 12,860 years. The period of the revolution of the celestial equinoctial pole about the pole of the ecliptic, is nearly 26,000 years; the north celestial pole, therefore, will be about 18,000 years; hence, nearly 49° from the present polar star.
189. For what is Ursa Minor distinguished? What said of its situation and change of position? 190. What said of the notice taken of it? Position of its principal star? Its Greek and Latin names, &c.? 191. Describe Polaris? How found? Remarks of Capt. Smyth respecting?
192. So general is the popular notion, that the North Polar Star is the true pole of the world, that even surveyors and navigators, who have acquired considerable dexterity in the use of the compass and the quadrant, are not aware that it ever had any deviation, and consequently never make allowance for any. All calculations derived from the observed position of this star, which are founded upon the idea that its bearing is always due north of any place, are necessarily erroneous, since it is in this position only twice in twenty-four hours; once when above, and once when below the pole.
193. Hence, it is evident that the surveyor who regulates his compass by the North Polar Star, must take his observation when the star is on the meridian, either above or below the pole, or make allowance for its altered position in every other situation. For the same reason must the navigator, who applies his quadrant to this star for the purpose of determining the latitude he is in, make a similar allowance, according as its altitude is greater or less than the true pole of the heavens; for we have seen that it is alternately half the time above and half the time below the pole.
194. The method of finding the latitude of a place from the altitude of the polar star, as it is very simple, is very often resorted to. Indeed, in northern latitudes, the situation of this star is more favorable for this purpose than that of any other of the heavenly bodies, because a single observation, taken at any hour of the night with a good instrument, will give the true latitude, without any calculation or correction, except that of its polar aberration.
If the polar star always occupied that point in the heavens which is directly opposite the north pole of the earth, it would be easy to understand how latitude could be determined from it in the northern hemisphere; for in this case, to a person on the equator, the poles of the world would be seen in the horizon. Consequently, the star would appear just visible in the northern horizon, without any elevation. Should the person now travel one degree toward the north, he would see one degree below the star, and he would think it had risen one degree.
And since we always see the whole of the upper hemisphere at one view, when there is nothing in the horizon to obstruct our vision, it follows that if we should travel 10° north of the equator, we should see just 10° below the pole, which would then appear to have risen 10°; and should we stop in the 42d degree of north latitude we should, in like manner, have our horizon just 42° below the pole, or the pole would appear to have an elevation of 42°. Whence we derive this general truth: The elevation of the pole of the equator is always equal to the latitude of the place of observation.
Any instrument, then, which will give us the altitude of the north pole, will give us also the latitude of the place.
The method of illustrating this phenomenon, is given in most treatises on the globe,
192. What popular error?
193. When is the pole star a safe guide for the surveyor or mariner? What allowances should be made by each? 194. What said of finding the latitude by observations upon the pole star? What general rule stated? Wha error committed?
and as adopted by teachers generally, is to tell the scholar that the north pole rises higher and higher, as he travels farther and farther toward it. In other words, whatever number of degrees he advances toward the north pole, so many degrees will it rise above his horizon. This is not only an obvious error in principle, but it misleads the apprehension of the pupil. It is not that the pole is elevated, but that our horizon is depressed as we advance toward the north. The same objection lies against the artificial globe; for it ought to be so fixed that the horizon might be raised or depressed, and the pole remain in its own invariable position.
195. Ursa Minor contains twenty-four stars, including three of the 3d magnitude and four of the 4th. The 'seven principal stars are so situated as to form a figure very much resembling that in the Great Bear, only that the Dipper is reversed, and about one half as large as the one in that constellation.
196. The first star in the handle, called Polaris, is the polar star, around which the rest constantly revolve. The two last in the bowl of the Dipper, corresponding to the Pointers in the Great Bear, are of the 3d magnitude, and situated about 15° from the pole. The brightest of them is called Kochab, which signifies an axle or hinge, probably in reference to its moving so near the axis of the earth.
Kochab may be easily known by its being the brightest and middle one of the three conspicuous stars forming a row, one of which is about 2°, and the other 3° from Kochab. The two brighest of these are situated in the breast and shoulder of the animal, about 8° apart, and are called the Guards or Pointers of Ursa Minor. They are on the meridian about the 20th of June, but may be seen at all hours of the night, when the sky is clear.
197. Of the four stars which form the bowl of the Dipper, one is so small as hardly to be seen. They lie in a direction toward Gamma in Cepheus; but as they are continually changing their position in the heavens, they may be much better traced out from the map, than from description.
Kochab is about 25° distant from Benetnasch, and about 24° from Dubhe, and hence forms with them a very nearly equilateral triangle.
"The Lesser Bear
Leads from the pole the lucid band: the stars
The prevailing opinion is that Ursa Major and Ursa Minor are the nymph Calisto and her son Arcas, and that they were transformed into bears by the enraged and imperious Juno, and afterward translated to heaven by the favor of Jupiter, lest they might be destroyed by the huntsmen.
The Chinese claim that the emperor Hong-ti, the grandson of Noah, first discovered
196. De195. Number of stars in Ursa Minor? Their magnitudes? How situated? scribe Polaris, Kochab, and the Guards or Pointers ? 197. Are all the stars distinctly visible? Direction? What triangle ?
HISTORY.-What prevailing opinion, or myth? Chinese claim? Phenicians? Greeks?
the polar star, and applied it to purposes of navigation. It is certain that it was used for this purpose in a very remote period of antiquity. From various passages in the ancients, it is manifest that the Phenicians steered by Cynosura, or the Lesser Bear; whereas, the mariners of Greece, and some other nations, steered by the Greater Bear, called Helice, or Helix.
Lucan, a Latin poet, who flourished about the time of the birth of our Saviour, thus adverts to the practice of steering vessels by Cynosura :
"Unstable Tyre now knit to firmer ground,
Ursa Major and Ursa Minor are sometimes called Triones, and sometimes the Greater and Lesser Wains. In Pennington's Memoirs of the learned Mrs. Carter, we have the following beautiful lines :
"Here Cassiopeia fills a lucid throne,
There, blaze the splendors of the Northern Crown;
O'er the pale countries of the frozen pole:
Whose faithful beams conduct the wandering ship
Thales, an eminent geometrician and astronomer, and one of the seven wise men of Greece, who flourished six hundred years before the Christian era, is generally reputed to be the inventor of this constellation, and to have taught the use of it to the Phenician navigators; it is certain that he brought the knowledge of it with him from Phenice into Greece, with many other discoveries both in astronomy and mathematics.
Until the properties of the magnet were known and applied to the use of navigation, and for a long time after, the north polar star was the only sure guide. At what time the attractive powers of the magnet were first known, is not certain; they were known in Europe about six hundred years before the Christian era; and by the Chinese records, it is said that its polar attraction was known in that country at least one thousand years earlier.
1. a URSA MINORIS (Polaris)-A DOUBLE STAR; R. A. 1h. 2m. 10s.; Dec. N. 88° 27′ 4′′. A 2%, topaz yellow; B 9%, pale white. Map VIII., Fig. 12.
2. BURSA MINORIS (Kochab)-A star with a distant companion in the left shoulder; R. A. 14h. 51m. 148.; Dec. N. 74° 48′ 2′′. A 8, reddish; B 11, pale grey-several small stars in the field.
8. d URSA MINORIS-A star with a very distant telescopic companion in the middle of the tail of the figure; R. A. 18h. 23m. 56s.; Dec. N. 86° 35' 4". A 8, greenish tinge; B 12, grey.
What proofs from the poets? What other names for Ursa Major and Ursa Minor? What said of Thales? Use of the pole star? The magnet?
TELESCOPIC OBJECTS.-Alpha? Show on the map, Beta-Delta-Epsilon-Zeta.
4. & URSE MINORIS-A star with a minute companion, at the root of the tail; R. A. 17h. 02m. 37s.; Dec. N. 82° 17′ 01′. A 4, bright yellow; B 12, pale blue; three ther telescopic stars in the field. It is easily found, being the third star from Polaris.
5. URSE MINORIS-A DOUBLE STAR in the middle of the body; R. A. 15h. 49m. 52s.; Dec. N. 78° 16' 07". A 4, flushed white; B 11, bluish with a yellow star of the 9th magnitude in the field.
CONSTELLATIONS ON THE MERIDIAN IN JULY.
SCORPIO (THE SCORPION).—MAP V.
198. THIS is the eighth sign, and ninth constellation, in the order of the Zodiac. It presents one of the most interesting groups of stars for the pupil to trace out that is to be found in the southern hemisphere. It is situated southward and eastward of Libra, and is on the meridian the 10th of July.
The sun enters this sign on the 23d of October, but does not reach the constellation before the 20th of November. When astronomy was first cultivated in the East, the two solstices and the two equinoxes took place when the sun was in Aquarius and Leo, Taurus and Scorpio, respectively.
199. Scorpio contains, according to Flamsted, forty-four stars, including one of the 1st magnitude, one of the 2d, and eleven of the 3d. It is readily distinguished from all others by the peculiar luster and the position of its principal stars.
Antares is the principal star, and is situated in the heart of the Scorpion, about 19° east of Zubenelgubi, the southernmost star in the Balance. Antares is the most brilliant star in that region of the skies, and may be otherwise distinguished by its remarkably red appearance. Its declination is about 26° S. It comes to the meridian about three hours after Spica Virginis, or fifty minutes after Corona Borealis, on the 10th of July. It is one of the stars from which the moon's distance is reckoned for computing the longitude at sea.
There are four great stars in the heavens, Fomalhaut, Aldebaran, Regulus, and Antares, which formerly answered to the solstitial and equinoctial points, and which were much noticed by the astronomers of the East.
200. About 84° northwest of Antares, is a star of the 2d
198. Order of Scorpio among the signs, &c.? Its comparative interest? Situation? When does the sun enter this sign? When the constellation? How with the solstices and equinoxes anciently? Why not so now? 199. Number and magnitudes of the stars in Scorpio? How distinguished? Name and position of its principal star? How known? What use made of it? What three other stars mentioned? 200. What other