Appendix L

THE EQUATION OF TIME

TABLE OF THE EQUATION OF TIME

--------+---------+---------+---------+---------+---------+-------- Day of | January |February | March | April | May | June Month | | | | | | --------+---------+---------+---------+---------+---------+-------- |m s |m s |m s |m s |m s |m s 1 |S 3 31 |S 13 44 |S 12 37 |S 4 6 |F 2 56 |F 2 30 6 |S 5 49 |S 14 15 |S 11 33 |S 2 37 |F 3 27 |F 1 41 11 |S 7 59 |S 14 27 |S 10 19 |S 1 14 |F 3 45 |F 0 44 16 |S 9 49 |S 14 19 |S 8 57 |F 0 4 |F 3 48 |S 0 18 21 |S 11 24 |S 13 52 |S 7 28 |F 1 12 |F 3 38 |S 1 23 26 |S 12 39 |S 13 10 |S 5 56 |F 2 10 |F 3 15 |S 2 27 31 |S 13 35 |S 12 13 |S 4 24 |F 2 56 |F 2 39 |S 3 38 --------+---------+---------+---------+---------+---------+--------

--------+---------+---------+---------+---------+---------+--------- Day of | July | August |September| October |November |December Month | | | | | | --------+---------+---------+---------+---------+---------+--------- |m s |m s |m s |m s |m s |m s 1 |S 3 28 |S 6 10 |S 0 6 |F 10 8 |F 16 18 |F 11 3 6 |S 4 24 |S 5 46 |F 1 31 |F 11 41 |F 16 17 |F 9 3 11 |S 5 11 |S 5 8 |F 3 13 |F 13 4 |F 15 56 |F 6 51 16 |S 5 46 |S 4 15 |F 4 58 |F 14 16 |F 15 13 |F 4 30 21 |S 6 9 |S 3 9 |F 6 45 |F 15 13 |F 14 10 |F 2 2 26 |S 6 11 |S 1 51 |F 8 29 |F 15 54 |F 12 45 |S 0 28 31 |S 6 12 |S 0 24 |F 10 8 |F 16 16 |F 11 3 |S 2 55 --------+---------+---------+---------+---------+---------+---------

As we have seen in Chapter X every day of the year is exactly 24 hours long by our clock time. The time by the Sun is usually either ahead or behind local clock time. The difference between clock time and Sun time is called the equation of time, and a table to show how many minutes and seconds the Sun is fast or slow, according to clock time, is given above, taken from “The New Astronomy,” by Professor Todd, who has kindly permitted me to use it here. In the table =S= means that the Sun is slow, that is, that the Sun does not cross the meridian until after the clock shows noon, and =F= means that the Sun is fast, that is, that the Sun has crossed the meridian before the clock shows noon. =m= means minutes, and =s= means seconds above the figures.

The table gives the average values of the equation of time, which may differ by a few seconds from the values for any particular year.