Day

The length of time occupied by a complete revolution of the earth on its axis. Some certain point is chosen to mark the commencement of the day, and, as this is arbitrary, we have several kinds of days and times to consider, owing to various selections.

Astronomical Day. The day commences at noon of the civil day and ends at noon--the hours being counted numerically from oh. to 24h.

Civil Day. The civil day begins at midnight and ends at midnight, the 24 hours being divided into two equal parts--the twelve from midnight to noon being named A. M. (before meridian), and the twelve from noon to midnight named P. M. (after meridian.)

Intercalary Day. A day inserted in the calendar in leap year.

Circumnavigators' Day. The day added to or subtracted from the date shown by the ship's log-book when the vessel crosses the meridian of 180 deg. in sailing easterly and westerly respectively.

Lunar Day. The interval of time between two successive transits of the moon over the same meridian.

Nautical Day. An old-fashioned way of keeping time at sea. The day began at noon, and was 12 hours in advance of the civil day and 24 hours in advance of the astronomical day. Now obsolete.

Sea Day. Same as nautical day.

Sidereal Day. The interval of time between two successive transits of a fixed star over the same meridian. Sometimes called a star day.

Solar Day. The interval of time between two successive transits of the sun's centre over the same meridian.