239. PROB. XV.—The month and day of the month being given, to find those places where the sun does not set, and where it does not rise on the given day. Find the sun's declination (by Prob. X.) elevate the pole for the declination, in the same manner as for the latitude; turn the globe on its axis, and on the places round the pole, above the horizon, the sun does not set; and on the places round the other pole, below the horizon, the sun does not rise, on that day. 1. How much of the south frigid zone is darkened, and how much of the north frigid zone is enlighted, on the 20 of May? Ans.-20° round each pole. 2. On which pole does the sun rise on Nov. 6. 3. Which frigid zone, and how much of it, has constant day, on August 4? 4. How much of the south frigid zone has constant day on the following days? 5. What days in the year does the sun shine equally on both poles? ART. 2. Problems to be solved by the celestial globe. 240. PROB. XVI.-To find the right ascension of the sun or a star. Bring the sun's place in the ecliptic or the star to the brass meridian, then the degrees of the equinoctial under the meridian, reckoning from Aries eastward, is the right ascension, 1. What is the sun's right ascension on the 19 of April? Ans.-27° 30′. 2. What is the sun's right ascension on the 1 Dec.? Ans.-247° 50. 241. PROB. XVII.-To find the declination of the sun or a star. Bring the sun's place in the ecliptic or the star to the brass meridian, and the degree of the meridian over that place will be the declination. 1. What is the declination of the sun, April 19? Ans.--11° 19'. 242. PROB. XVIII.-The latitude of the place, the day and hour being given, to place the globe so as to represent the appearance of the heavens at that time at the place; and to point out the situations of the several stars. Elevate the pole for the latitude of the place; find the sun's place in the ecliptic, and bring it to the me ridian, and set the index to 12; if the time be afternoon, turn the glooe westward; if in the forenoon, turn it eastward, till the index points to the given hour. The surface of the globe then represents the appearance of the heavens at that place. 1. Represent the appearance of the heavens for Jan. 13, 4 o'clock A. M. and 8 o'clock P. M. 2. August 30, at 9 o'clock P. M. 3. November 3, at 3 o'clock A. M. 4. May 16, at midnight. 243. PROB. XIX.--To find the latitude or longitude of a given star. Screw the quadrant on the pole of the ecliptic, bring the star to the meridian, and the degrees of the quadrant between the ecliptic and star, show the latitude, and the degree of the ecliptic under the graduated edge of the quadrant is the longitude. 1. What is the latitude and longitude of Arcturus? Ans.--Latitude 31° north. Longitude 201°. 2. What are the latitudes and longitudes of Fomalhaut, Canis Major, Regulus? QUESTIONS. SECT. I. 1 What does the true Solar System consist of? 2 How do primary planets and comets differ from secondary planets, moons, or satellites? 3 How many primary planets are there? 4 Name them. 5 How many secondary planets are there? 6 How are they distributed in the solar system? Is the number of the comets known? 8 What is the centre of the solar system? 9 In what direction do primary planets move round the sun? 10 What is the path of a heavenly body called? 11 In what direction do secondary planets revolve? 12 Have comets a particular direction? 13 What is the form of the planets' orbits? Explain. 14 Is the sun in the centre? 15 What is the lower focus? -16 What is the upper? 17' When is a heavenly body said to be in its perihelion? 18 When in its aphelion? 19 When is the moon said to be in perigee ?-20 When in apogee? 21 What is the eccentricity of an orbit? (see fig.) 22 What is the figure of all the planets, except the Earth? 23 How is this known of all except the Earth? 24 How is it known of the Earth? 25 Have all the planets another motion besides that round the Sun? 26 What are axes? 27 Do large bodies, or small ones, generally turn quickest on their axes? 28 What are the extremities of an axis called? 29 Does the Sun appear to describe the same circle among the stars, which the Earth describes ? 30 With what difference? Illustrate. 31 What is this circle called? 32 What is the plane passing through this circle called? 33 How many degrees in a circle? 34 How many minutes in a degree?36 How many signs in the Ecliptic? -35 Seconds, in a minute? 37 How many degrees in each sign? 38 Repeat the signs in order. (See fig.) 39 In what sign is the aphelion of each planet? (See frontispiece.) 40 Do all the primary planets revolve in the Ecliptic? 41 What is the Zodiac? Describe it. 42 Are all the planets always in the Zodiac? 43 Mention the exceptions. 44 What are nodes?45 Descending?46 Ascending? SECT. II. 47 By what light are the planets seen? 48 What does the different distances of the planets from the sun occasion ? 49 By what law do heat and light decrease? Explain. 50 Can this be proved? -51 Prove it. 52 What variation in the appearance of the Sun's disk? 53 What does the alternate appearance and disappearance of spots on the Sun's disk prove? 54 In what time does the Sun turn on his axis? 55 Do the spots change in appearance ? 56 Is their cause known? 57 What is the zodiacal light? Describe it. 58 When is it most distinct? 59 In what region is it always visible 60 Is its cause known? SECT. III. 61 Proceeding from the sun, which is the first planet? 62 What is the mean distance of Mercury from the Sun ? 63 In what time does it revolve round the sun?-64 Turn on its axis? 65 What is the colour of its light? 66 Why is it not often seen? 67 What is its greatest elongation?! 68- What is the degree of heat and light at Mercury, compared with that of the Earth? -69 What would become of water there? SECT. IV. 70 What is the mean distance of Venus? 71 In what time doos it revolve round the sun? 72 In what time does it turn on its axis? 73 What is said of the light reflected by this planet? 74 What is its greatest elongation? 75 What is the comparative portion of heat and light at Venus? |