mark, as directed on former occafions; and bring the fun's place to the Eastern verge of the horizon. If Venus be in antecedence of the fun, according to the order of the figns, that is, e. g. in Taurus when the fun is in Gemini, fhe will rife before the fun, and in that pofition will be a morning ftar. But if Venus be in confequence of the fun, according to the order of the figns, that is, e. g. in Gemini when the fun is in Taurus, fhe will set after the fun, and in that position she will be an evening ftar. The pupil fhould be here reminded, that, in confequence of the earth's diurnal motion being from Weft to Eaft, the heavenly bodies appear to move from Eaft to Weft; of courfe Aries will come to the Eastern part of the horizon, to the meri. dian, and to the Western part of the horizon, be fore Taurus; Taurus before Gemini, &c. &c. By examining an ephemeris through the feveral months of the year, according to the above plan, it may eafily be feen when Venus rifes before or after the fun, and of course how long, in that year, the continues an evening or a morning ftar. For inftance, in White's Ephemeris, for the year 1797, it appears that Venus was in antecedence of the fun from January the 1ft till May the 29th; and confequently during that period fhe was a morning ftar; after that time, through the remainder of the year, he was in confequence of the fun, and was therefore an evening ftar from the 29th of May till the expiration of December; a circumftance which is noticed in the fecond page of the ephemeris. PROBLEM PROBLEM CIV. To find in a given Latitude, and on an affigned Day, how long Venus rifes or fets before or after the Sun, according as he is a Morning or an Evening Star. Adjuft the globe for the given latitude and the fun's place at noon; find by an ephemeris the place of Venus, and upon the correfponding part of the ecliptic append her aftronomical character. If Venus be, at the given period, a morning ftar, bring her defignating mark to the Eaftern part of the horizon, and the index will fhew the time of her rifing revolve the globe till the fun's place reaches the fame femicircle of the horizon, and the index will indicate the time of his rifing: the difference of these periods is the fpace which Venus rifes before the fun. : If Venus be an evening ftar on the affigned day, bring the fun's place to the Western part of the horizon, and remark the time by the index; turn the globe till Venus arrives at the fame femicircle of the horizon, and notice the time; the difference of these periods is the space she fets after the fun. EXAMPLES. How long did Venus fet after the fun at London, November 30, 1797, her fituation being then 23o in Capricornus, and the fun's place 8° in Sagittarius -Anf. About 8 hours. 3 Required how long, in the year 1800, Venus rifes before the fun at London, January 23-Feb. A a 19-- -19-March 12-April 11-May 5-June 13July 6-August 23-Sept. 12-and how long the fets after him at the fame place on the following days: Oct. 11-Nov. 3-Dec. 17. N. B. The pupil may afcertain the truth of thefe operations by confulting the ephemeris for the rifing and fetting of the fun and Venus on the above days. How to know the chief Stars, and to find the North Pole. If any one ftar be known, the others may be found by confidering first some of the nearest stars that lie round it, whether they make a triangle or a quadrangle, ftraight lines, or curves, right angles, or oblique angles, with the known ftar. This is eafily done by comparing the stars on the globe (being rectified to the hour of the night) with the prefent face of the heavens, and the fituations of the ftars there, as directed in Problem 85. It is by this method alfo, that we learn to know fome points in the heavens where no ftar is. For example, the North Pole, which is easily found by means of Charles's Wain, i. e. feven ftars in the conftellation Urfa Major *. Four of those ftars in a quadrangle are fuppofed to represent a cart or waggon, b, r, c, d, in the annexed figure; and the three others the horses. The ftar a is called Alioth; d is denominated Dubhe; b and rare called the two guards or pointers, because they point directly in a straight line to the North pole p, which now is near 2 degrees distant from the far s, which is called the North pole ftar +. + See page 140. * See page 297. The The North pole may also be found by the ftar Aliath, from which a ftraight line, drawn to the pole far s, goes through the pole point p, and leaves it at 24 degrees diftance from the pole ftar. It may also be found by the little ftar n, which is the nearest ftar to the pole ftar s; for a line drawn from a to s is the hypothenufe of a right-angled triangle, whofe right angle is in the pole point p. |