Aphelion (Aph.): The point in a planet’s
orbit that is farthest from the Sun.
Apogee (Apo.): The point in the Moon’s
orbit that is farthest from Earth.
Celestial Equator (Eq.): The imaginary
circle around the celestial sphere that
can be thought of as the plane of Earth’s
equator projected out onto the sphere.
Celestial Sphere: An imaginary sphere
projected into space that represents the
entire sky, with an observer on Earth at
its center. All celestial bodies other than
Earth are imagined as being on its inside
surface.
Conjunction: The time at which two or
more celestial bodies appear closest in
the sky. Inferior (Inf.): Mercury or Venus
is between the Sun and Earth. Superior
(Sup.): The Sun is between a planet and
Earth. Actual dates for conjunctions are
given in the Right-Hand Calendar Pages,
115– 141; the best times for viewing the
closely aligned bodies are given in the
SKY WATCH section of the Left-Hand Cal-
endar Pages, 114– 140.
Declination: The celestial latitude of an
object in the sky, measured in degrees
north or south of the celestial equator;
analogous to latitude on Earth. The
Almanac gives the Sun’s declination at
noon.
Eclipse, Lunar: The full Moon enters the
shadow of Earth, which cuts off all or
part of the sunlight reflected off the
Moon. Total: The Moon passes com-
pletely through the umbra (central dark
part) of Earth’s shadow. Partial: Only
part of the Moon passes through the um-
bra. Penumbral: The Moon passes
through only the penumbra (area of par-
tial darkness surrounding the umbra).
See page 98 for more eclipse information.
Eclipse, Solar: Earth enters the shadow of
the new Moon, which cuts off all or part
of the Sun’s light. Total: Earth passes
through the umbra (central dark part) of
the Moon’s shadow, resulting in totality
for observers within a narrow band on
Earth. Annular: The Moon appears sil-
houetted against the Sun, with a ring of
sunlight showing around it. Partial: The
Moon blocks only part of the Sun.
Ecliptic: The apparent annual path of the
Sun around the celestial sphere. The
plane of the ecliptic is tipped 231⁄ 2° from
the celestial equator.
Elongation: The difference in degrees be-
tween the celestial longitudes of a planet
and the Sun. Greatest Elongation (Gr.
Elong.): The greatest apparent distance
of a planet from the Sun, as seen from
Earth.
Epact: A number from 1 to 30 that indicates
the Moon’s age on January 1 at Green-
wich, England; used for determining the
date of Easter.
Equinox: When the Sun crosses the celes-
tial equator. This event occurs two times
each year: Vernal is around March 21
and Autumnal is around September 23.
Evening Star: A planet that is above the
western horizon at sunset and less than
180° east of the Sun in right ascension.
Golden Number: A number in the 19-year
cycle of the Moon, used for determining
the date of Easter. (Approximately every
19 years, the Moon’s phases occur on the
same dates.) Add 1 to any given year and
divide by 19; the remainder is the
Golden Number. If there is no remain-
der, the Golden Number is 19.
Greatest Illuminated Extent (Gr. Illum.
Ext.): When the maximum surface area of
a planet is illuminated as seen from Earth.
Julian Period: A period of 7,980 years be-
ginning January 1, 4713 B.C. It provides
a chronological basis for the study of an-
cient history. To find the Julian year, add
4,713 to any year.
Midnight: Astronomical midnight is the
time when the Sun is opposite its highest
References:
Archives