. Fig. 6.—TOTAI, eclipse OK 11111. SHOWING CORON'.\. Reproduced, by permission, from the ''Monthly Notices " of Ih: Royal Astronomical Society. are in the same months year by year, an implication contrary to experience. The nodes are continually changing their positions, with the effect that the eclipse seasons come about eighteen or twenty days earlier in succeeding years. This can be seen if we tabulate the eclipses for a year or two. Year. Date. I92I April April Oct. 8 22 I Sun Moon Sun 1922 Oct. Mar. 16 28 Moon Sun 1923 Sept. Mar. Mar. 20 3 17 Sun Moon Sun Aug. Sept. 26 10 Moon Sun 1
. Fig. 6.—TOTAI, eclipse OK 11111. SHOWING CORON'.\. Reproduced, by permission, from the ''Monthly Notices " of Ih: Royal Astronomical Society. are in the same months year by year, an implication contrary to experience. The nodes are continually changing their positions, with the effect that the eclipse seasons come about eighteen or twenty days earlier in succeeding years. This can be seen if we tabulate the eclipses for a year or two. Year. Date. I92I April April Oct. 8 22 I Sun Moon Sun 1922 Oct. Mar. 16 28 Moon Sun 1923 Sept. Mar. Mar. 20 3 17 Sun Moon Sun Aug. Sept. 26 10 Moon Sun 1 Mean. April 15 Oct. 8 I Mar. ID J Sept. The maximum number of eclipses that can occur near any one mean date is three; there cannot ' The " nodes " are the points in which the orbit of the moon cuts the plane of the ecliptic, or the orbit of the earth. normally be more than six in a year, a number not often reached. Occasionally, however, there may be seven, but only if the eclipse seasons come either in January and July, when there may be overlapping from the succeeding year, or in June and December, when there may just come in an extra one from the previous year. This greatest possible number, seven, was reached in 1917, and will be reached again in 1935. It was reached once in the nineteenth century. According to civil time, 1805 had seven, but as the first occurred at I on January i, it would count as in 1804 according to astronomical reckoning, in which the day is regarded as beginning at noon. But as against this, 1823 had six according to the civil reckoning, and seven according to the astronomical, the last occurring at 8 o'clock on the morning of New Year's Day 1824, a time astronomers would call 20 o'clock on December 31, 1823. We may, therefore, count either 1805 or 1823 as having had seven eclipses, according to the system we adopt, but we cannot fairly count both. It may be mentioned in passing that this dual system of reckoning is to terminate at
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