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morning of the 11th. Georgium Sidus will be stationary on the 16th, and Venus on the 20th. Mercury will be in conjunction with a in Virgo at 40 m. after 8 in the evening of the 19th, when the star and planet will be so nearly in a line with each other as only to be separated by an apparent angle of 31, which Mercury will be south of the star. This planet will also attain his greatest elongation on the 25th, and the Moon will be in conjunction with Jupiter at 56 m. past 10 at night on the 27th.
REFLECTIONS ON THE STARRY HEAVENS.
(Continued from page 241.] To ascertain the places of the stars, and point them out in the heavens, astronomers generally make use of two quantities, which they call Declination and Right Ascension. A great circle is supposed to pass through the two poles and the centre of each star, cutting the equator at right angles. This is called the circle of declination; and the arc of it, included between the equator and the star, is that which measures its declination. This declination is therefore of two kinds, north and south, às the star is situated on the north or south side of the equinoctial line. Those stars that are at the same distance from the equator have, consequently, equal declinations. From knowing the declination of any star, and the latitude of the place, or, which answers the same purpose, the altitude of the equator (which is equal to the colatitude), the meridional altitude of the star may be easily found. To find the real place of a star, however, another circle is requisite, on which its distance east or west is measured from some fixed point. The circle of declination passing through the point of the equator where it is intersected by the ecliptic, called the vernal equinoctial point, is that fixed upon by astronomers for the commence
ment of this measure. The arc of the equator included between the vernal equinox and the circle of declination that passes through the star, is called its Right Ascension. This is reckoned from the point of its commencement eastward quite round the heavens; and is either expressed in degrees and minutes, or time, but frequently the latter: these, however, are readily converted into each other. When both the right ascension and declination are known, the place of the star is determined, and it may consequently be pointed out in the heavens. When latitude and longitude are used, they are referred to the equinoctial point and the ecliptic, in the same way as to that point and the equator for right ascension and declination. If a star have the same right ascension as the Sun has, they will come to the meridian at the same time; but from the earth's annual motion in its orbit, the Sun appears to advance eastward among the stars at the rate of nearly a degree a day, which is equal to four minutes of time; so that this causes the stars to pass the meridian each day four minutes sooner than on the preceding day. Those stars, for instance, that are on the meridian at midnight, will, the next night, arrive at the same point four minutes before twelve the following night, eight minutes, &c. If, therefore, the heavens be viewed at the same hour of any two nights, six months distant from each other, they will present opposite hemispheres, and, consequently, a completely different assemblage of stars, with the exception of such as never set, in the latitude of observation.
Astronomers have divided the starry firmament into sections similar to countries on the surface of the earth: these divisions they denominate constellations, each of them including a number of stars that lie contiguous to each other; so that, by a knowledge of these, the particular parts of the starry heavens are readily referred to on celestial maps, in the same manner as countries are pointed out on
maps of the terrestrial globe. For a list of the constellations we must refer to the INTRODUCTION of our volume for 1815. The stars in each constellation are also distinguished by the letters of the Greek alphabet, a being annexed to the largest, B to the next in size, y to the third, and so on for the others. New stars are also referred to by means of the letters in the Roman alphabet. In briefly describing a few of these constellations, we shall avail ourselves of the valuable information presented in an, excellent Celestial Atlas, recently published by Alexander Jamieson, A.M., to which we also refer our readers for a more copious account of the starry assemblages; assuring such of them as feel an interest in the subject, that they will by no means lose their labour in its perusal.
URSA MAJOR. . Ursa Major, or the Great Bear, is one of those constellations that never set in these latitudes. It constantly revolves about the north pole, taking all possible positions in each diurnal revolution, and presenting one of the finest objects in the northern part of the heavens. By some this constellation is thought to be Calisto, an attendant upon Diana, the goddess of hunting; others suppose it to represent Arcas, the son of Jupiter and Calisto. The antients are said to have represented each of the constellations of the bears under the form of a waggon drawn by a team of horses; and the Great Bear is still best known in many parts of this country as Charles's Wain. In some places it is also called the plough, to which a strong resemblance may certainly be traced. It appears to have been of Egyptian origin, and various conjectures have been formed in reference to the reasons for introducing this animal into the heavens; the most plausible seems to be, that the northern regions of the earth being the noted haunts of the bear, it might be thought the fittest
the north Revolutio the nortbe is
symbol for containing the pole of the world, as well as for that constellation which should serve as an index to point out that pole. It is easily distinguished by seven bright stars, four of which, d, B, 7, 8, form the angles of a quadrilateral figure; the others, &, 3, no form a curve line nearly in the direction of one of the diagonals of the quadrilateral. This last is situated in the upper and hinder part of the body of the Bear, while the curve forms the tail. Alpha and beta, which constitute the side of the quadrilateral opposite the tail, are called the pointers, because they direct the eye to a bright star P in the tail of the Little Bear, which is situated near the north pole. This will readily be perceived by an inspection of the lower figure in the subjoined diagram, which represents Ursa Major when immediately below the pole. The seven stars in the upper figure in the diagram also represent Ursa Minor, which are obviously placed under a similar figure to those of Ursa Major, but at only about half the dimensions of the latter sign.
in the Minor,
This constellation contains eighty-seven stars, one of which is of the 1st magnitude, four of the 2d, three of the 3d, and ten of the 4th; all the others
belong to the inferior classes. When the constellation is considered under the idea of Charles's Wain, the four bright stars, a, b, y, and d, are the wheels, and the other three represent the shafts and horses; but, as the Great Bear, its tail is marked out by these three, the back and body by the other four: there are also others of the 3d and 4th magnitude that mark the outlines of the figure with much precision. The upper pointer is of the 2d magnitude, and, like those in the tail, has its particular name; it is called Dubhe. The middle one in the tail is Mizar, and appears double. As the southern extremity of this sign approaches within 32° of the equator, and the northern to 72° of north declination, it therefore becomes vertical to Europe, most of Asia, and North America, during each diurnal revolution of the earth, and no part of the animal sinks below the horizon except his right hind leg. · In 1820, Dubhe («) had 62° 43' 17'' of north declination, and 163° 7' 6" of right ascension. It culminated, or came to the meridian above the pole, at London, for the first day of each month in that year, as in the following table, with a meridian altitude of 78° 47' 43":
h. January -. 4 February - 1 March -- 0 April ... 10 May -... 8 June- ... 6
t . . . - 2 15 •--
By adding 12 hours to the times given in the preceding list, we shall have the moments when the same star was on the meridian below the pole.
URSA MINOR. Ursa Minor, or Cynosura, the Little Bear, according to the antient fable, represents Arcas, the