Equation Of Time, the difference between apparent time, determined by the meridian passage of the real sun, and mean time, determined by the passage of the mean sun. It goes through a double period in the course of a year. Its amount varies a fraction of a minute for the same date, from year to year and from one longitude to another, on the same day. The following table shows an average value for any date and for the Greenwich meridian for a number of years, from which the actual value will seldom deviate more than 20 seconds until after 1950. The + sign indicates that the real sun reaches the meridian after mean noon; the − sign before mean noon.
Table of the Equation of Time.
| m. | s. | m. | s. | m. | s. | ||||||
| Jan. | 1 | +3 | 26 | Mar. | 1 | +12 | 39 | May | 1 | −2 | 55 |
| 6 | 5 | 45 | 6 | 11 | 35 | 6 | −3 | 27 | |||
| 11 | 7 | 51 | 11 | 10 | 20 | 11 | −3 | 46 | |||
| 16 | 9 | 43 | 16 | 8 | 58 | 16 | −3 | 51 | |||
| 21 | 11 | 19 | 21 | 7 | 30 | 21 | −3 | 40 | |||
| 26 | 12 | 36 | 26 | 5 | 59 | 26 | −3 | 16 | |||
| Feb. | 1 | +13 | 42 | Apr. | 1 | +4 | 9 | June | 1 | −2 | 32 |
| 6 | 14 | 14 | 6 | 2 | 40 | 6 | −1 | 44 | |||
| 11 | 14 | 25 | 11 | +1 | 15 | 11 | −0 | 48 | |||
| 16 | 14 | 17 | 16 | −0 | 3 | 16 | +0 | 14 | |||
| 21 | 13 | 52 | 21 | −1 | 12 | 21 | 1 | 19 | |||
| 26 | 13 | 11 | 26 | −2 | 10 | 26 | 2 | 24 | |||
| July | 1 | +3 | 26 | Sept. | 1 | +0 | 9 | Nov. | 1 | −16 | 18 |
| 6 | 4 | 21 | 6 | −1 | 28 | 6 | −16 | 19 | |||
| 11 | 5 | 8 | 11 | −3 | 10 | 11 | −15 | 58 | |||
| 16 | 5 | 44 | 16 | −4 | 55 | 16 | −15 | 15 | |||
| 21 | 6 | 8 | 21 | −6 | 41 | 21 | −14 | 12 | |||
| 26 | 6 | 18 | 26 | −8 | 25 | 26 | −12 | 49 | |||
| Aug. | 1 | +6 | 10 | Oct. | 1 | −10 | 5 | Dec. | 1 | −11 | 7 |
| 6 | 5 | 47 | 6 | −11 | 38 | 6 | −9 | 9 | |||
| 11 | 5 | 9 | 11 | −13 | 2 | 11 | −6 | 57 | |||
| 16 | 4 | 17 | 16 | −14 | 14 | 16 | −4 | 35 | |||
| 21 | 3 | 12 | 21 | −15 | 11 | 21 | −2 | 7 | |||
| 26 | 1 | 55 | 26 | −15 | 52 | 26 | +0 | 23 | |||
