1.
Semi-major and semi-minor axes
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In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction

2.
238P/Read
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238P/Read is a main-belt comet discovered on 2005 October 24 by M. T. Read using the Spacewatch 36 inch telescope on Kitt Peak and it has an orbit within the asteroid belt and has displayed the coma of a traditional comet. It fits the definition of an Encke-type comet with, before it was discovered 238P came to perihelion on 2005 July 27. When it was discovered on 2005 October 24, it showed vigorous cometary activity until 2005 December 27, outgassing likely began at least 2 months before discovery. The activity of 238P is much stronger than 133P/Elst-Pizarro and 176P/LINEAR and this may indicate that the impact assumed to have triggered 238Ps activity occurred very recently. Observations of 238P when it was inactive in 2007 suggests that it has a small nucleus only about 0.6 km in diameter and it last came to perihelion on 2011 March 10, and will next come to perihelion on 2016 October 22. 238P/Read was the target of a proposal in NASAs Discovery Program in the 2010s called Proteus. Discovery programs founding mission was to an asteroid, but it went to a Near-Earth asteroid, a mission to a main-belt asteroid was proposed in the 1990s

3.
87P/Bus
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Comet 87P/Bus is a periodic comet with an orbital period of 6.5 years. It fits the definition of an Encke-type comet with and it was discovered by Schelte J. Bus in 1981 on a plate taken with the 1. 2m UK Schmidt telescope at Siding Spring, Australia. The discovery was announced in IAU Circular 3578 on March 4,1981 and it has been observed on each of its subsequent apparitions, most recently in 2013. Orbital simulation from JPL / Horizons Ephemeris 87P/Bus – Seiichi Yoshida @ aerith. net

4.
Comet Encke
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Comet Encke or Enckes Comet is a periodic comet that completes an orbit of the Sun once every 3.3 years. Like most comets, it has a low albedo, reflecting only 4. 6% of the light it receives. The diameter of the nucleus of Enckes Comet is 4.8 km, as its official designation implies, Enckes Comet was the first periodic comet discovered after Halleys Comet. It was independently observed by astronomers, the second being Caroline Herschel in 1795. Its orbit was calculated by Johann Franz Encke, who through laborious calculations was able to link observations of comets in 1786,1795,1805 and 1818 to the same object. In 1819 he published his conclusions in the journal Correspondance astronomique and it was recovered by Carl Ludwig Christian Rümker at Parramatta Observatory on 2 June 1822. Comets are in orbits that evolve over time due to perturbations. Given Enckes low orbital inclination near the ecliptic and brief orbital period of 3 years, Enckes orbit gets as close as 0.17309 AU to Earth. On 4 July 1997, Encke passed 0.19 AU from Earth, on 18 November 2013, it passed 0.02496 AU from Mercury. Close approaches to Earth usually occur every 33 years, the failed CONTOUR mission was launched to study this comet, and also Schwassmann-Wachmann 3. On April 20,2007, STEREO-A observed the tail of Comet Encke to be torn off by magnetic field disturbances caused by a coronal mass ejection. The tail grew back due to the shedding of dust. Comet Encke is believed to be the originator of several related meteor showers known as the Taurids, a shower has similarly been reported affecting Mercury. Near-Earth object 2004 TG10 may be a fragment of Encke, measurements on board the NASA satellite MESSENGER have revealed Encke may contribute to seasonal meteor showers on Mercury. The Mercury Atmospheric and Surface Composition Spectrometer instrument discovered seasonal surges of calcium since the probe began orbiting the planet in March 2011. The spikes in calcium levels are thought to originate from small dust particles hitting the planet, however, the general background of interplanetary dust in the inner Solar System cannot, by itself, account for the periodic spikes in calcium. This suggests a source of additional dust, for example. More than one theory has associated Enckes Comet with impacts of cometary material on Earth, the Tunguska event of 1908, probably caused by the impact of a cometary body, has also been postulated by Czechoslovakian astronomer Ľubor Kresák as a fragment of Comet Encke

5.
82P/Gehrels
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82P/Gehrels is a periodic comet that was discovered on October 27,1975 by Tom Gehrels at the Palomar Mountain Observatory in California having a faint nuclear brightness of magnitude 17. Calculations based on the early sightings gave a perihelion of 23 April 1975. It was observed by J. Gibson on its next predicted apparition in 1984, using the 122-cm Schmidt at Palomar and it has since been observed in 1993,2001 and 2010. The object has been identified as a comet, which means it is near a 3,2 mean-motion resonance with the planet Jupiter. It fits the definition of an Encke-type comet with and it has an estimated diameter of 1.46 km. On 15 August 1970 the comet passed 0.00143 AU from Jupiter, list of numbered comets Orbital simulation from JPL / Horizons Ephemeris

6.
94P/Russell
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94P/Russell 4 is a periodic comet in the Solar System. It fits the definition of an Encke-type comet with and it was discovered by Kenneth S. Rusell on photographic plates taken by M. Hawkins on March 7,1984. In the discovery images, Russell estimated that the comet had an apparent magnitude of 13, in the year of discovery, the comet had come to perihelion in January 1984. With an aphelion of 4.7 AU, comet 94P currently has an orbit contained completely inside of the orbit of Jupiter, in July 1995, 94P was estimated to have a radius of about 2.6 km with an absolute magnitude of 15.1. It may have a very elongated nucleus with a ratio of a/b >=3