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A lunar phase or Moon phase is the apparent shape of the Moon 's directly sunlit portion as viewed from the Earth (because the Moon is tidally locked with the Earth, the same hemisphere is always facing the Earth). In common usage, the four major phases are the new moon, the first quarter, the full moon and the last quarter; the four minor ...
Lunar theory. Lunar theory attempts to account for the motions of the Moon. There are many small variations (or perturbations) in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now be modeled to a very high degree of accuracy (see section Modern developments).
Every 18.6 years, the angle between the Moon's orbit and Earth's equator reaches a maximum of 28°36′, the sum of Earth's equatorial tilt (23°27′) and the Moon's orbital inclination (5°09′) to the ecliptic. This is called major lunar standstill. Around this time, the Moon's declination will vary from −28°36′ to +28°36′.
The phases of Venus result from the planet's orbit around the Sun inside the Earth 's orbit giving the telescopic observer a sequence of progressive lighting similar in appearance to the Moon's phases. It presents a full image when it is on the opposite side of the Sun. It is a gibbous phase when it approaches or leaves the opposite side of the ...
The geocentric model was the predominant description of the cosmos in many European ancient civilizations, such as those of Aristotle in Classical Greece and Ptolemy in Roman Egypt, as well as during the Islamic Golden Age. Two observations supported the idea that Earth was the center of the Universe.
The Antikythera mechanism (/ ˌæntɪkɪˈθɪərə / AN-tik-ih-THEER-ə, US also / ˌæntaɪkɪˈ -/ AN-ty-kih-) [1][2] is an Ancient Greek hand-powered orrery (model of the Solar System). It is the oldest known example of an analogue computer [3][4][5] used to predict astronomical positions and eclipses decades in advance. [6][7][8] It could ...
Planetary phase. The evolution of the apparent diameter and phases of Venus. A planetary phase is a certain portion of a planet 's area that reflects sunlight as viewed from a given vantage point, as well as the period of time during which it occurs. The phase is determined by the phase angle, which is the angle between the planet, the Sun and ...
Lunar eclipse. A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. [1] Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Earth's orbit.