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twilight

(Encyclopedia)twilight, period between sunset and total darkness or between total darkness and sunrise. Total darkness does not occur immediately when the sun sinks below the horizon because light from the sun that...

Orion, in astronomy

(Encyclopedia)Orion, in astronomy, constellation located on the celestial equator. It is one of the most conspicuous and easily recognizable constellations in the entire sky. From ancient times it has been mentione...

node

(Encyclopedia)node, in astronomy, point at which the orbit of a body crosses a reference plane. One reference plane that is often used is the plane of the earth's orbit around the sun (ecliptic). Since the moon's o...

declination

(Encyclopedia)declination, in astronomy, one of the coordinates in the equatorial coordinate system. The declination of a celestial body is its angular distance north or south of the celestial equator measured alon...

inclination

(Encyclopedia)inclination, in astronomy, the angle of intersection between two planes, one of which is an orbital plane. The inclination of the plane of the moon's orbit is 5°9′ with respect to the plane of the ...

antipodes, in geography

(Encyclopedia)antipodes [Gr.,=having feet opposite], people or places diametrically opposite on the globe. Thus antipodes must be separated by half the circumference of the earth (180°), and one must be as far nor...

right ascension

(Encyclopedia)right ascension, in astronomy, one of the coordinates in the equatorial coordinate system. The right ascension of a celestial body is the angular distance measured eastward from the vernal equinox alo...

La Condamine, Charles Marie de

(Encyclopedia)La Condamine, Charles Marie de shärl märēˈ də lä kôNdämēnˈ [key], 1701–74, French traveler and mathematical geographer. He was one of a group sent to Peru in 1735 to measure the length of ...

Canis Minor

(Encyclopedia)Canis Minor [Lat.,=lesser dog], small constellation ying near the celestial equator, E of Orion and NE of Canis Major, the Large Dog. Known as the Small Dog, Canis Minor is traditionally identified as...

snowball earth

(Encyclopedia)snowball earth, hypothesized condition in which the earth was covered completely by ice during several periods in the Proterozoic. The hypothesis was originally developed to explain evidence of the co...