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This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a ...
r a is the radius at apoapsis (also "apofocus", "aphelion", "apogee"), i.e., the farthest distance of the orbit to the center of mass of the system, which is a focus of the ellipse. r p is the radius at periapsis (or "perifocus" etc.), the closest distance.
Ulugh Beg was notable for his work in astronomy-related mathematics, such as trigonometry and spherical geometry, as well as his general interests in the arts and intellectual activities. [ 1 ] [ 2 ] It is thought that he spoke five languages: Arabic , Persian , Chaghatai Turkic , Mongolian , and a small amount of Chinese . [ 3 ]
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (from Ancient Greek ἐπίκυκλος (epíkuklos) 'upon the circle', meaning "circle moving on another circle") [1] was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets.
The lunar orbit's major axis – the longest diameter of the orbit, joining its nearest and farthest points, the perigee and apogee, respectively – makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct motion) – meaning precesses eastward by 360°.
Apogee Books, an imprint of Canadian publishing house Collector's Guide Publishing; Apogee Electronics, a manufacturer of digital audio hardware systems; Apogee Software, a video game publisher and developer now known as 3D Realms; Apogee Entertainment, a video game publisher that acquired the rights to the name and logo from 3D Realms
In present-day astrology, the name Lilith or Black Moon Lilith is usually given to a point on the horoscope of the actual Moon's apogee.When considered as a point, this Lilith is sometimes defined as the second focus of the ellipse described by the Moon's orbit; the Earth is the first focus, and the apogee lies in the same approximate direction as the focus.
Astrophysicist Fred Espenak uses Nolle's definition but preferring the label of full Moon at perigee, and using the apogee and perigee nearest in time rather than the greatest and least of the year. [13] Wood used the definition of a full or new moon occurring within 24 hours of perigee and also used the label perigee-syzygy. [7]