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Semi-major axis. 17.737 au ... Halley's Comet is the only known short ... Researchers in 1981 attempting to calculate the past orbits of Halley by numerical ...
For elliptical orbits it can also be calculated from the periapsis and apoapsis since = and = (+), where a is the length of the semi-major axis. = + = / / + = + where: 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.
is the length of the semi-major axis, is the standard gravitational parameter. Conclusions: For a given semi-major axis the specific orbital energy is independent of the eccentricity. Using the virial theorem to find: the time-average of the specific potential energy is equal to −2ε
The comet passed perihelion on 8 July. C. S. Morris reported the comet on 15 July had a tail 50 arcminutes long with two components. [5] The comet faded in August as it moved both away from Earth and the Sun and by the end of the month its magnitude was reported to be around 10. The comet continued to fade slowly and was reported to be mag. 13.
Orbit determination has a long history, beginning with the prehistoric discovery of the planets and subsequent attempts to predict their motions. Johannes Kepler used Tycho Brahe's careful observations of Mars to deduce the elliptical shape of its orbit and its orientation in space, deriving his three laws of planetary motion in the process.
Newton also applied his theorem to the planet Mercury, [26] which has an eccentricity ε of roughly 0.21, and suggested that it may pertain to Halley's comet, whose orbit has an eccentricity of roughly 0.97. [25] A qualitative justification for this extrapolation of his method has been suggested by Valluri, Wilson and Harper. [25]
The semi-major axis (major semiaxis) is the longest semidiameter or one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter. The semi-minor axis (minor semiaxis) of an ellipse or hyperbola is a line segment that is at right angles with the semi-major axis and has one end at the center of the conic section.
Uranus has an axial tilt of 97.77°, so its axis of rotation is approximately parallel with the plane of the Solar System. The reason for Uranus's unusual axial tilt is not known with certainty, but the usual speculation is that it was caused by a collision with an Earth-sized protoplanet during the formation of the Solar System. [6]