The time of sunrise or sunset may be found for any day by elevating the north or south pole equal to the sun's declination north or south for any given day. The place being under the brass meridian, the hour circle should be set at XII., and then the place should be rotated first to the eastern horizon and then to the western and the times on the hour circle noted, the former being the time of rising, and the latter that of setting of the sun. Twice the time of setting of the sun gives the length of the day, and twice the time of rising gives the length of the night.

Example: 20th January, 1890, sun rose, 8.15; set, 3.45.

2 X 3.45 = 7½ = length of day. 2 X 8.15 = 16½ = length of night.

The months and days of the months are all marked on the ecliptic, so that the sun's place for any day is determined by finding the day on the ecliptic and noting the part of the sign of the zodiac corresponding to that day, and if the globe be turned till this part of the ecliptic comes to the meridian, the latter will indicate the declination of the sun.

Note

The Analemma is a convenient projection of the ecliptic on which the sun's declination may be readily found, as it is noted for every day in the year.

Numerical Facts Relating To The Sun

Solar Parallax (equatorial horizontal), 8.80" ± 0.02". Mean distance of the sun from the earth, 92,885,000 miles; 149,480,000 kilometers. Variation of the distance of the sun from the earth between January and June, 3,100,000 miles; 4,950,000 kilometers.

Linear value of 1" on the sun's surface, 450.3 miles; 724.7 kilometers. Mean angular semi-diameter of the sun, 16' 02.0". Sun's linear diameter, 866,400 miles; 1,394,300 kilometers. (This may, perhaps, be variable to the extent of several hundred miles.) Ratio of the sun's diameter to the earth's, 109.3. Surface of the sun compared with the earth, 11,940. Volume, or cubic contents, of the sun compared with the earth, 1,305,000. Mass, or quantity of matter, of the sun compared with the earth, 330,000 ±3000. Mean density of the sun compared with the earth, 0.253. Mean density of the sun compared with water, 1.406. Force of gravity on the sun's surface compared with that on the earth, 27.6. Distance a body would fall in one second, 444.4 feet; 135.5 meters. Inclination of the sun's axis to the ecliptic, 7° 15'. Longitude of its ascending node, 74°. Date when the sun is at the node, June 4, 5. Mean time of the sun's rotation (Carrington), 25.38 days. Time of rotation of the sun's equator, 25 days. Time of rotation at latitude 20°, 25.75 days. Time of rotation at latitude 30°, 26.5 days. Time of rotation at latitude 45°, 27.5 days. (These last four numbers are somewhat doubtful, the formulae of various authorities giving results differing by several hours in some cases.) Linear velocity of the sun's rotation at his equator, 1.261 miles per second; 2.028 kilometers per second. Total quantity of sunlight, 1,575,-000,000,000,000,000,000,000,000 candles. Intensity of the sunlight at the surface of the sun, 190,000 that of a candle flame; 5300 times that of metal in a Bessemer converter; 146 times that of a calcium light; 3.4 times that of an electric arc. Brightness of a point on the sun's limb compared with that of a point near the center of the disk, 25 per cent. Heat received per minute from the sun upon a square meter, perpendicularly exposed to the solar radiation, at the upper surface of the earth's atmosphere (the solar constant), 25 calories. Heat radiation at the surface of the sun, per square meter per minute, 1,117,-000 calories. Thickness of a shell of ice which would be melted from the surface of the sun per minute, 48½ feet, or 14¾ meters. Mechanical equivalent of the solar radiation at the sun's surface, continuously acting, 109,000 horse power per square meter; or, 10,000 (nearly) per square foot. Effective temperature of the solar surface (according to Rossetti), about 10,000° C, or 18,000 F.

Nebular Hypothesis

According to this theory, all the members of our solar system once existed in a state of highly heated gaseous or nebulous matter, which extended far beyond the orbit of our most remote planet, Neptune. This matter was supposed to have received a motion of rotation, and, as it cooled, became more and more condensed, the central portion leaving a ring of protuberant matter in the equatorial region, which, after becoming detached, would continue to revolve in the same direction as the parent mass, something after the fashion of Saturn's ring. This detached ring, it was presumed, would break up, and collecting into a globular mass retain its motion of rotation, and take up an additional motion of revolution around its primary. The detached planets formed in this way would, by a similar process, throw off their satellites, which, after long ages of cooling, have assumed their present state.