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The Sun's gravitational effect on the Moon is more than twice that of Earth's on the Moon; consequently, the Moon's trajectory is always convex [25] [26] (as seen when looking Sunward at the entire Sun–Earth–Moon system from a great distance outside Earth–Moon solar orbit), and is nowhere concave (from the same perspective) or looped.
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Diagram of the Moon's phases: The Earth is at the center of the diagram and the Moon is shown orbiting. When the Sun and Moon are aligned on the same side of the Earth (conjunct), the Moon is "new", and the side of the Moon facing Earth is
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.
As seen from Earth, the planet's orbital prograde motion makes the Sun appear to move with respect to other stars at a rate of about 1° eastward per solar day (or a Sun or Moon diameter every 12 hours). [nb 1] Earth's orbital speed averages 29.78 km/s (19 mi/s; 107,208 km/h; 66,616 mph), which is fast enough to cover the planet's diameter in 7 ...
The Moon is Earth's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period (lunar month) with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth.
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First there is a real retardation of the Moon's angular rate of orbital motion, due to tidal exchange of angular momentum between Earth and Moon. This increases the Moon's angular momentum around Earth (and moves the Moon to a higher orbit with a lower orbital speed). Secondly, there is an apparent increase in the Moon's angular rate of orbital ...