D

Day. The interval of time between two successive passages of a star over the meridian is a
Sidereal day 23h, 56m of mean solar time). The interval between two successive passages of the
Sun's center over the same meridian is a solar day (24 hours); of the Moon's center a lunar day
(24h, 50m). In old astrological texts the Lunar Day refers to the day of the Full Moon. Because
of the Earth's motion in orbit the mean solar day is 4 minutes longer than the sidereal day and
because of the Moon's daily motion in orbit the lunar day is 50 minutes longer than the solar
day. The term natural day is a misnomer, loosely applied to the 24-hour period of the Earth's
rotation. The mean solar day becomes the civil day when reckoned from the hour affixed by law.
In most countries this is from midnight to midnight. With the Hindus and Babylonians it was
from sunrise to sunrise; with the Athenians and Jews from sunset to sunset; with the ancient
Egyptians and Romans at midnight. This is divided into 24 hourly divisions from 1 to 12 noon,
and 1 to 12 midnight.

Army and Navy time during recent years has been largely superceded by numbering the hours
straight through from 0h at midnight to 24h of the next midnight; which also is 0h of the next
day.

Astronomical Day. Until January 1, 1925, this day was reckoned as beginning 12 hours later
than the civil day. Now all calendars and almanacs begin the day at midnight.

Julian Day. On January 1, 1925, the astronomical day was superseded by the Julian day,
numbered consecutively beginning from 4713 B.C. To avoid confusion in the comparison of
ancient and modern dates the Julian day was made to begin at noon, twelve hours later than the
civil day. January 1, 1934, was J.D. 2,427,439.

Civil Day. The civil day begins at midnight at 180 east or west from Greenwich. It then
continues one hour later with every 15° of the Sun's westward travel. Thus when one passes this
International Date Line he begins a day that will not end until 24 hours later, with the result that
when it becomes Tuesday to the west of the Line it has just become Monday to the east thereof,
and circumnavigating travelers gain or lose a day according to their direction of travel; losing a
day if westbound, gaining it when eastbound.

Loosely speaking, a day is the period of light between sunrise and sunset, the period of daylight
or sunshine. In the Far East it is the distance that can be traveled in 24 hours.

In astrological parlance a Day Horoscope is one cast for a birth moment in which the Sun was
above the horizon, hence in one of the Houses numbered from 7 to 12; a Night Horoscope one in
which the Sun is below the horizon, in a House numbered between 1 and 6.