Project SpaceZ

     ___    _____     ___
    /_ /|  /____/ \  /_ /|       Horizons On-line Ephemeris System v4.68
    | | | |  __ \ /| | | |       Solar System Dynamics Group
 ___| | | | |__) |/  | | |__     Jet Propulsion Laboratory
/___| | | |  ___/    | |/__ /|   Pasadena, CA, USA
|_____|/  |_|/       |_____|/

Background Information

• albedo albedo Definition Albedo is ratio of the light received by a body to the light reflected by that body. Albedo values range from 0 (pitch black) to 1 (perfect reflector). Technical Definition Geometric albedo is the ratio of a body’s brightness at zero phase angle to the brightness of a perfectly diffusing disk with the same position and apparent size as the body. Examples Our Moon has a very low albedo (0.07), while Venus has a high albedo (0.60). The albedo combined with the absolute magnitude can help determine the size of an asteroid.
• aphelion aphelion Definition An orbit’s farthest point to the Sun.
• argument of perihelion argument of perihelion Definition Angle in the orbit plane between the ascending node and the perihelion point.
• ascending node ascending node Definition Point on the orbit where the object “ascends” through the ecliptic plane, passing from below it to above it.
• au (Astronomical Unit) au (Astronomical Unit) Definition The astronomical unit (au) is defined by the IAU as exactly 149,597,870,700 m. Notes It is approximately the average distance between the Earth and the Sun (about 150 billion meters). The IAU has specified that this term is lower-case “au”, so “AU” is techincally incorrect.
• B-plane B-plane Definition Plane perpendicular to the asymptote of the incoming hyperbolic trajectory of the object relative to the Earth.
• descending node descending node Definition Point on the orbit where the object “descends” through the ecliptic plane, passing from above it to below it.
• eccentricity eccentricity Definition One half of the major axis of the elliptical orbit; also the mean distance from the Sun.
• ecliptic plane ecliptic plane Definition Plane of the Earth’s orbit.
• ephemeris ephemeris Definition An ephemeris is a tabulation of computed positions and velocities (and/or various derived quantities such as right ascension and declination) of an orbiting body at specific times. The plural form of ephemeris is ephemerides.
• H (absolute magnitude) H (absolute magnitude) Definition An asteroid’s absolute magnitude is the visual magnitude an observer would record if the asteroid were placed 1 Astronomical Unit (au) away, and 1 au from the Sun and at a zero phase angle. Technical Definition The magnitude of an asteroid at zero phase angle and at unit heliocentric and geocentric distances.
• inclination inclination Definition Angle between the orbit plane and the ecliptic plane.
• keyhole keyhole Definition A usually narrow region of a pre-impact b-plane in which the gravitational effect of the encounter puts the asteroid on a trajectory which impacts at a later encounter. In other words, if the object passes through a keyhole in one b-plane, it is on course to collide with the Earth at the potentially impacting encounter.
• LD (Lunar Distance) LD (Lunar Distance) Definition The term LD (Lunar Distance) refers to the average distance between the Earth and Moon. For data reported on this site, we use a mean semimajor axis for the moon of 384400 km (~.002570 au) to define one LD.
• line of nodes line of nodes Definition The line of intersection between the orbit plane and the plane of the ecliptic (the Earth’s orbit plane). (Not defined if orbit lies exactly in the plane of the ecliptic.)
• longitude of the ascending node longitude of the ascending node Definition Angle in the ecliptic plane between the inertial-frame x-axis and the line through the ascending node.
• NEO (Near-Earth Object) NEO (Near-Earth Object) Definition An asteroid or comet with a perihelion distance less than or equal to 1.3 au. 99% of NEOs are asteroids. See our page on NEO Groups for more information.
• nodal points nodal points Definition The two points at which an orbit crosses through the ecliptic. The potential impact occurs at one of these points.
• perigee perigee Definition A trajectory’s closest point to the Earth.
• perihelion perihelion Definition An orbit’s closest point to the Sun.
• period period Definition The time it takes an orbiting body to make one complete revolution around the Sun.
• PHA (Potentially Hazardous Asteroid) PHA (Potentially Hazardous Asteroid) Definition Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid’s potential to make threatening close approaches to the Earth. Specifically, all asteroids with a minimum orbit intersection distance (MOID) of 0.05 au or less and an absolute magnitude (H) of 22.0 or less are considered PHAs. See our page on NEO Groups for more information.
• semi-major axis semi-major axis Definition One half of the major axis of the elliptical orbit; also the mean distance from the Sun.
• true anomaly true anomaly Definition Angle in the orbit plane between the perihelion point and the position of the orbiting object.

---