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The term retrograde is from the Latin word retrogradus – "backward-step", the affix retro-meaning "backwards" and gradus "step". Retrograde is most commonly an adjective used to describe the path of a planet as it travels through the night sky, with respect to the zodiac , stars, and other bodies of the celestial canopy .
Most of the material orbits and rotates in one direction. This uniformity of motion is due to the collapse of a gas cloud. [1] The nature of the collapse is explained by conservation of angular momentum. In 2010 the discovery of several hot Jupiters with backward orbits called into question the theories about the formation of planetary systems. [2]
The average distance between Neptune and the Sun is 4.5 billion km (about 30.1 astronomical units (AU), the mean distance from the Earth to the Sun), and it completes an orbit on average every 164.79 years, subject to a variability of around ±0.1 years. The perihelion distance is 29.81 AU, and the aphelion distance is 30.33 AU.
All the spheres rotate around the Sun, which is near the centre of the Universe. The distance between the Earth and the Sun is an insignificant fraction of the distance from the Earth and the Sun to the stars, so parallax is not observed in the stars. The stars are immovable; their apparent daily motion is caused by the daily rotation of the Earth.
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2. The Law of Equal Areas in Equal Time: A line that connects a planet to the Sun sweeps out equal areas in equal times. 3. The Law of Harmony: The time required for a planet to orbit the Sun, called its period, is proportional to long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.
The use of astronomical symbols for the Sun and Moon dates to antiquity. The forms of the symbols that appear in the original papyrus texts of Greek horoscopes are a circle with one ray for the Sun and a crescent for the Moon. [3] The modern Sun symbol, a circle with a dot (☉), first appeared in Europe in the Renaissance. [3]
In this hypothesis, as the binary system approaches Neptune, it becomes unbound by tidal forces; one component of the binary is ejected from the system, and Triton is captured into a highly eccentric orbit around Neptune. For this to occur, the escaping companion must be massive enough to provide the impulse needed for a single pass capture ...