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An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. [1] The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. (See also the Amor asteroids.)
Aten asteroids are defined by having a semi-major axis (a) of less than 1.0 astronomical unit (AU), the roughly average distance from the Earth to the Sun. They also have an aphelion (Q; furthest distance from the Sun) greater than 0.983 AU. [1] This defines them as Earth-crossing asteroids as the orbit of Earth varies between 0.983 and 1.017 AU.
Satellites in geostationary orbit. From the list in the first section, these are the closest known asteroids per year that approach Earth within one lunar distance.More than one asteroid per year may be listed if its geocentric distance [note 1] is within a tenth of the lunar distance, or 0.10 LD.
1221 Amor / ˈ æ m ɔːr / is an asteroid and near-Earth object on an eccentric orbit, approximately 1 kilometer (0.6 miles) in diameter. It is the namesake of the Amor asteroids, the second-largest subgroup of near-Earth objects.
As an eccentric Amor asteroid has an Earth minimum orbit intersection distance of 0.1922 AU (28,800,000 km) and approaches the orbit of Earth from the outside but does not cross it. It crosses however the orbit of Mars and can be classified as a Mars-crosser and also approaches the orbit of Jupiter within 0.5 AU. [ 1 ]
Common orbital subgroups of Near-Earth Objects (NEOs). Atira asteroids / ə ˈ t ɪr ə / or Apohele asteroids, also known as interior-Earth objects (IEOs), are Near-Earth objects whose orbits are entirely confined within Earth's orbit; [1] that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's perihelion (nearest point to the Sun), which is 0.983 astronomical ...
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth (a > 1 AU ) but perihelion distances less than the Earth's aphelion distance (q < 1.017 AU).
The most common and best-known class is the trojan, which librates around one of the two stable Lagrangian points (Trojan points), L 4 and L 5, 60° ahead of and behind the larger body respectively. Another class is the horseshoe orbit, in which objects librate around 180° from the larger body. Objects librating around 0° are called quasi ...