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Old 04-04-2012, 09:55 PM   #88
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Lightbulb Triaxial ellipsoids

An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known...2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt...Mathematical literature often uses 'ellipsoid' in place of 'tri-axial ellipsoid'...Older literature uses 'spheroid' in place of 'ellipsoid of revolution'...If the ellipse is rotated about its major axis, the result is a prolate (elongated) spheroid, like a Rugby ball...Several moons of the Solar system approximate prolate spheroids in shape, though they are actually scalene. Examples are Mimas, Enceladus, and Tethys (satellites of Saturn) and Miranda (a satellite of Uranus)...It is also used to describe the shape of some nebulae (nebulas) such as the Crab Nebula.

Haumea, formal designation 136108 Haumea, is a dwarf planet one-third the mass of Pluto...Haumea and its two moons. Hiʻiaka is above Haumea, and Namaka is directly below...At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka periodically occulting Haumea...

But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape...Haumea's extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, thereby meeting the definition of a dwarf planet.

Haumea has a typical orbit for a classical Kuiper-belt object, with an orbital period of 283 Earth years, a perihelion of 35 AU, and an orbital inclination of 28°. It passed aphelion (Apis) in early 1992, and is currently more than 50 AU from the Sun...

...An apsis is the point of greatest or least distance of a body from one of the foci of its elliptical orbit...Derivative terms are used to identify the body being orbited. The most common are perigee and apogee , referring to orbits around the Earth (Greek γῆ, gê, "earth"), and perihelion and aphelion , referring to orbits around the Sun (Greek ἥλιος, hēlios, "sun"). During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon...

With a visual magnitude of 17.3, Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.


The perihelion and aphelion of the Earth...

For the orbit of the Earth around the sun, the time of apsis is often expressed in terms of a time relative to seasons, since this determines the contribution of the elliptical orbit to seasonal variations. The variation of the seasons is primarily controlled by the annual cycle of the elevation angle of the sun, which is a result of the tilt of the axis of the Earth measured from the plane of the ecliptic.

Traditionally, the three types of conic section are the hyperbola, the parabola, and the ellipse.

Lastly, Haumea is the goddess of fertility and childbirth, with many children who sprang from different parts of her body; this corresponds to the swarm of icy bodies thought to have broken off the dwarf planet during an ancient collision. The two known moons, also believed to have formed in this manner, are thus named after two of Haumea's daughters, Hiʻiaka and Nāmaka

Last edited by lightgiver; 04-04-2012 at 10:09 PM.
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