Archive image from page 309 of Discovery Discovery discovery0304londuoft Year: 300 DISCOVERY whilst that of 1330 was the shortest, lasting 4 sees, short of a minute. An interesting point in connection with eclipses, both lunar and solar, is the times at which they occur in anv particular year. These are grouped into two chief divisions, separated by about six months, and known as the ' Eclipse Seasons.' Eclipses can occur onlj' when the sun is near a node, and this happens only twice in the year. Hence we have the general rule that in any year there are two dominant eclipses separated by ab
Archive image from page 309 of Discovery Discovery discovery0304londuoft Year: 300 DISCOVERY whilst that of 1330 was the shortest, lasting 4 sees, short of a minute. An interesting point in connection with eclipses, both lunar and solar, is the times at which they occur in anv particular year. These are grouped into two chief divisions, separated by about six months, and known as the ' Eclipse Seasons.' Eclipses can occur onlj' when the sun is near a node, and this happens only twice in the year. Hence we have the general rule that in any year there are two dominant eclipses separated by about six months, whilst others may occur a fortnight before or a fortnight after them. This might seem to imply that the eclipse seasons 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.
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