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This unique spiral galaxy, which is situated 3.2 billion light-years from the Earth, has an extended stream of bright blue knots and diffuse wisps of young stars. [2] It rushes at 3.6 million km/h (1000km/s [2]) through the cluster Abell 2667 and therefore, like a comet, shows a tail, with a length of 600,000 light-years.
Comets whose aphelia are near a major planet's orbit are called its "family". [81] Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits. [82] At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet.
Periodic comets usually have elongated elliptical orbits, and usually return to the vicinity of the Sun after a number of decades. The official names of non-periodic comets begin with a "C"; the names of periodic comets begin with "P" or a number followed by "P". Comets that have been lost or disappeared have names with a "D". Comets whose ...
These comets come from the Kuiper belt and scattered disk, beyond the orbit of Pluto, with possible origins in the Oort cloud for many. For comets with an orbital period of over 1000 years (semi-major axis greater than ~100 AU), see the List of near-parabolic comets.
However, in April 1996 the comet passed within 0.77 AU (115 million km) of Jupiter, close enough for its orbit to be measurably affected by the planet's gravity. [35] The comet's orbit was shortened considerably to a period of roughly 2,399 years, [4] and it will next return to the inner Solar System around the year 4385. [7]
The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun. [36] It was also one of the earliest successful tests of Newtonian physics, and a clear demonstration of its explanatory power. [37] The comet was first named in Halley's honour by French astronomer Nicolas-Louis de Lacaille in ...
The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 days. [h] However, because the Earth–Moon system moves at the same time in its orbit around the Sun, it takes slightly longer, 29.5 days, [i] [72] to return to the same lunar phase, completing a full cycle, as seen from Earth.
By 1900 comets were categorized as "periodic", with elliptical orbits, or "non-periodic", one-time with parabolic or hyperbolic orbits. Astronomers believed that planets captured non-periodic comets into elliptical orbits; each planet had a "family" of comets that it captured, with Jupiter's the largest.