EXPLANATION OF EXAMPLE 3. On page IV of the Nautical Almanac, January 20th, the moon's meridian passage is 19h 48m, which shows that the moon passes the meridian of Greenwich on the 21st at 7h 48m A.M. Then of course the astronomical date and time would be 20d 19h 48m. To this add the correction 10m for longitude 5 hours west, which gives the moon's upper transit at the meridian of Boston, to which is added the high water interval, 11h 27m, and the result will be the astronomical date and time of high water, which is 21d 07h 25m, and being less than 12 hours is also civil time P.M. To the moon's upper transit at the meridian of Boston, 20d 19h 58m, add the low water interval, 5h 17m, which gives the astronomical date and time of low water, 21d 01h 15m, and being less than 12 hours is also civil time P.M. The lower transit is found by adding together the moon's meridian passages for the 19th and the 20th, taking care to include the days and dividing by 2, which gives the moon's lower transit at Greenwich, to which is added the correction 10m for longitude 5 hours west, and to this add the high water interval, 11h 27m, and the result will be the astronomical date and time of high water, which is 20d 18h 57m. Add 1 day and subtract 12 hours to convert the astronomical time into civil time the 21st, 6h 57m A.M. To the moon's lower transit at the meridian of Boston, 20d 7h 30m, add the low water interval, 5h 17m, which gives the astronomical date and time of low water, which is 20d 12h 47m. To this add 1 day and subtract 12 hours to convert the astronomical time into civil time the 21st, Oh 47m A.M. |