ECLIPSE, an interception or obscura tion of the light of the sun, moon or other heavenly body by the intervention of another and non-luminous heavenly body or by its shadow. An eclipse of a star or planet is called occultation. Eclipses may be divided into three classes: solar, lunar, and planetary.
Solar Eclipses.—An eclipse of the sun is an occultation of part of the face of the sun, occasioned by an interposition of the moon between the earth and the sun; thus all eclipses of the sun happen at the time of the new moon. The dark or central part of the moon's shadow, where the sun's rays are wholly inter cepted, is called the umbra, and the light part, where only a part of them are in tercepted, is called the penumbra; and it is evident that if a spectator be situated on that part of the earth where the um bra falls, there will be a total eclipse of the sun at that place; in the penumbra there will be no eclipse. As the earth is not always at the same distance from the moon, if an eclipse should happen when the earth is so far from the moon that the rays of light proceeding from the upper and lower limbs of the sun across each other before they reach the earth, a spectator situated on the earth in a di rect line between the centers of the sun and moon, would see a ring of light around the dark body of the moon; such an eclipse is called annular; when this happens there can be no total eclipse anywhere, because the moon's umbra does not reach the earth. situ ated in the penumbra will perceive a partial eclipse; an eclipse can never be annular longer than 12 minutes 24 sec onds, nor total longer than 7 minutes 58 seconds; nor can the duration of any eclipse of the sun exceed two hours. An
eclipse of the sun begins on the W. side of his disk and ends on the E.; and an eclipse of the moon begins on the eastern side of her disk and ends on the western. The average number of eclipses in a year is four, two of the sun and two of the moon; and as the sun and moon are as long below the horizon of any particular place as they are above it, the average number of visible eclipses in a year is two, one of the sun and one of the moon. Total eclipses of the sun offer brief but intensely interesting phenomena for the astronomer's study. The nature of the sun's corona is as yet undetermined, and the aid of the spectroscope and of photog raphy has not been sufficiently applied to the settling of the various problems presented. There were solar eclipses May 18, 1901, Aug. 30, 1905, Aug. 21, 1914, June 8, 1918, May 29, 1919.
Lunar Eclipses.—An eclipse of the moon is an obscuration of the light of the formerly used to determine longitudes since they are the same viewed from all parts of the earth. The dates of a num ber of important events of antiquity have been approximately determined by calculations concerning eclipses recorded at or near the time. Eclipses have been calculated up to the year 2161.