(66391) 1999 KW₄ ((66391) 1999 KW₄, also written (66391) 1999 KW4) is an Aten and Mercury-crosser asteroid discovered by LINEAR in 1999. It is interesting for two reasons. The word linear comes from the Latin word linearis, which means created by lines. ... May 20 is the 140th day of the year in the Gregorian Calendar (141st in leap years). ... 1999 is a common year starting on Friday Anno Domini (or the Current Era), and was designated the International Year of Older Persons by the United Nations. ... The provisional designation of comets and asteroids are similar to each other: they both follow a pattern set in 1925 by the Minor Planet Center of the IAU. Historical designations At first, astronomers strove to assign symbols to the minor planets: 1 Ceres a stylized sickle 2 Pallas a lozenge... Minor planets, or planetoids are minor bodies of the Solar system orbiting the Sun (or of other planetary systems orbiting other stars) that are larger than meteoroids (the largest of which might be taken to be around 10 meters or so across) but smaller than major planets (Mercury having a... The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten, discovered January 7, 1976 by Eleanor F. Helin). ... A Mercury-crosser asteroid is an asteroid whose orbit crosses that of Mercury. ... A Venus-crosser asteroid is an asteroid whose orbit crosses that of Venus. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... July 14 is the 195th day (196th in leap years) of the year in the Gregorian Calendar, with 170 days remaining. ... 2004(MMIV) is a leap year starting on Thursday of the Gregorian calendar. ... The Julian day or Julian day number (JDN) is the number of SI days that have elapsed since 12 noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC in the proleptic Julian calendar 1. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ... Giga (symbol: G) is a prefix in the SI system of units denoting 109, or 1 000 000 000. ... The metre, or meter, is the basic unit of length in the International System of Units (SI: Système International dUnités). ... The astronomical unit (AU or au or a. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... See also Day (language) A day (symbol: d) is a unit of time. ... A Julian year is the length of an average year in the Julian calendar, 365. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... The second (symbol s) is a unit for time, and one of seven SI base units. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... A degree (or in full a degree of arc), usually symbolized °, is a measurement of plane angle, representing 1/360 of a full rotation. ... The Longitude of the ascending node () is one of the orbital elements used to specify the orbit of an object in space. ... The argument of the perihelion is one of the orbital elements describing the orbit of a planet. ... In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. ... Mass iz a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... A cubic centimetre (cm3) is an SI derived unit of volume, equal to the volume of a cube with side length of 1 centi metre. ... It has been suggested that Law of universal gravitation be merged into this article or section. ... In physics, for a given gravitational field and a given position, the escape velocity is the minimum speed an object without propulsion, at that position, needs to have to move away indefinitely from the source of the field, as opposed to falling back or staying in an orbit within a... In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis. ... Asteroids are assigned a type based on spectral shape, color, and sometimes albedo. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standardized distance away. ... The albedo is a measure of reflectivity of a surface or body. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... The title of this article is incorrect due to technical limitations. ... In ancient times, only the Sun and Moon, a few hundred stars and the most easily visible planets had names. ... The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten, discovered January 7, 1976 by Eleanor F. Helin). ... A Mercury-crosser asteroid is an asteroid whose orbit crosses that of Mercury. ... The word linear comes from the Latin word linearis, which means created by lines. ... 1999 is a common year starting on Friday Anno Domini (or the Current Era), and was designated the International Year of Older Persons by the United Nations. ...

First, 1999 KW₄ is one of the few asteroids whose orbit crosses that of Mercury, the innermost planet (another is 1566 Icarus). Its unusual, eccentric orbit suggests that the asteroid may in fact be a comet that has lost its surface ice and can no longer produce a tail. For additional meanings, see Mercury (disambiguation). ... 1566 Icarus is an Apollo asteroid (a sub-class of near-Earth asteroid) whose unusual characteristic is that at perihelion it is closer to the Sun than Mercury; it is said to be a Mercury-crosser asteroid. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... Photo of the comet Hale-Bopp above a tree. ...

Radar images of asteroid 1999 KW₄ and its moon. The 'streaks' on the image are the moon's trail as it moved while the images were created.

Second, despite its small size (about 1.2 km in diameter), 1999 KW₄ has a small moon orbiting it. The moon, designated S/2001 (66391) 1 is only 360 m in diameter, and orbits 1999 KW₄ in 0.758 d (16 hours) at a distance of 2.6 km and a leisurely speed of 0.25 m/s (0.9 km/h). The companion was first suggested by an apparent eclipsing binary signal in photometric observations made June 19-27, 2000 by Petr Pravec and Lenka Šarounová at Ondrejov Observatory. It was confirmed by radar observations from Arecibo Observatory from May 21-23, 2001 by Lance A. M. Benner, Steven J. Ostro, Jon D. Giorgini, Raymond F. Jurgens, Jean-Luc Margot and Michael C. Nolan, announced on May 23, 2001. Radar images of asteroid 1999 KW4 and its moon. ... Radar images of asteroid 1999 KW4 and its moon. ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... June 19 is the 170th day of the year (171st in leap years) in the Gregorian Calendar, with 195 days remaining. ... June 27 is the 178th day of the year (179th in leap years) in the Gregorian calendar, with 187 days remaining. ... This article is about the year 2000. ... Petr Pravec is a Czech astronomer. ... Lenka Å arounová (* 1973) is a Czech astronomer. ... The Arecibo Observatory is located in Arecibo, Puerto Rico on the north coast of the island. ... May 21 is the 141st day of the year in the Gregorian calendar (142nd in leap years). ... May 23 is the 143rd day of the year in the Gregorian calendar (144th in leap years). ... 2001: A Space Odyssey. ... Steven J. Ostro is an astronomer at the Jet Propulsion Laboratory of the National Aeronautics and Space Administration. ... Jean-Luc Margot is a Belgian astronomer and an Assistant Professor at Cornell University. ... May 23 is the 143rd day of the year in the Gregorian calendar (144th in leap years). ... 2001: A Space Odyssey. ...

References

• http://www.johnstonsarchive.net/astro/astmoons/am-66391.html
• The another rader image of 1999 KW₄