Celestial poleThe north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively.
Right ascensionIn astronomy, Right ascension (abbreviated RA; symbol α) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the Earth. When paired with declination, these astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system.
Equatorial coordinate systemThe equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fundamental plane consisting of the projection of Earth's equator onto the celestial sphere (forming the celestial equator), a primary direction towards the Marchequinox, and a right-handed convention.
Celestial equatorThe celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of a planet, by convention generally Earth. By extension, it is also a plane of reference in the equatorial coordinate system.
HorizonMost commonly, the horizon is the border between the surface of a celestial body and its sky when viewed from the perspective of an observer on or above the surface of the celestial body. This concept is further refined as: The true or geometric horizon, which an observer would see if there was no alteration from refraction or from obstruction by intervening objects. The geometric horizon assumes a spherical earth.Angular distanceAngular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors – typically in three-dimensional space – or the central angle subtended by the radii through two points on a sphere. When the rays are lines of sight from an observer to two points in space, it is known as the apparent distance or apparent separation.
Celestial sphereIn astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.
Epoch (astronomy)In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to perturbations and vary with time.
Hour circleIn astronomy, the hour circle is the great circle through a given object and the two celestial poles. Together with declination and distance (from the planet's centre of mass), it determines the location of any celestial object. As such, it is a higher concept than the meridian as defined in astronomy, which takes account of the terrain and depth to the centre of Earth at a ground observer's location.
LatitudeInternational Terrestrial Reference SystemSpatial Reference System Identifier (SRID)Universal Transverse Mercator (UTM)
AstronomyAstronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation.
Minute and second of arcA minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol ′, is a unit of angular measurement equal to 1/60 of a degree. Since one degree is 1/360 of a turn, or complete rotation, one arcminute is 1/21600 of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth; therefore, the actual Earth's circumference is approximately 21600 nmi.*As an Amazon Associate I earn from qualifying purchases.