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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.
Representation of Venus (yellow) and Earth (blue) circling around the Sun. Venus and its rotation in respect to its revolution. Venus has an orbit with a semi-major axis of 0.723 au (108,200,000 km; 67,200,000 mi), and an eccentricity of 0.007.
The equant point (shown in the diagram by the large • ), is placed so that it is directly opposite to Earth from the deferent's center, known as the eccentric (represented by the × ). A planet or the center of an epicycle (a smaller circle carrying the planet) was conceived to move at a constant angular speed with respect to the equant.
The angles for Earth, Uranus, and Venus are approximately 23°, 97°, and 177° respectively. In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbital plane ...
The origin is the Sun's center, the plane of reference is the ecliptic plane, and the primary direction (the x-axis) is the March equinox. A right-handed rule specifies a y-axis 90° to the east on the fundamental plane. The z-axis points toward the north ecliptic pole. The reference frame is relatively stationary, aligned with the March equinox.
Venus is similar in size and distance from the sun when compared with Earth, and some researchers believe the planet might have even had an Earth-like climate at some point. But “Earth’s twin ...
Venus currently has a surface temperature of 450℃ (the temperature of an oven’s self-cleaning cycle) and an atmosphere dominated by carbon dioxide (96%) with a density 90 times that of Earth’s.
In astronomy, perturbation is the complex motion of a massive body subjected to forces other than the gravitational attraction of a single other massive body. [1] The other forces can include a third (fourth, fifth, etc.) body, resistance, as from an atmosphere, and the off-center attraction of an oblate or otherwise misshapen body.