Spherical astronomy

The airmass in astronomy quantifies the path length that the light from a celestial source must travel through the Earth's atmosphere to get to the observatory, relative to that for a source at the zenith. ...more on Wikipedia about "Airmass"

An Almucantar, also spelled almucantarat or almacantara, is a circle on the celestial sphere parallel to the horizon. Two stars that lie the same almucantar have the same altitude. ...more on Wikipedia about "Almucantar"

In astronomy and surveying, altitude (sometimes called elevation) is one of the two coordinates of the horizontal coordinate system, and refers to the vertical angle from the horizon. The other coordinate is azimuth, which refers to the horizontal angle from the north. ...more on Wikipedia about "Altitude (astronomy)"

The antisolar point is the imaginary point on the celestial sphere exactly opposite the sun. It is where anticrepuscular rays appear to converge, and on a moonless night away from city lights, it is often possible to see the gegenschein there. ...more on Wikipedia about "Antisolar point"

The autumnal equinox (or fall equinox) marks the beginning of astronomical autumn. It occurs during the month of September in the Northern Hemisphere, and during March in the Southern Hemisphere. In Chinese culture it marks the middle of autumn. At the same moment that the autumnal equinox occurs in one hemisphere, it is the time of the vernal equinox in the other hemisphere. ...more on Wikipedia about "Autumnal equinox"

Azimuth is the horizontal component of a direction ( compass direction), measured around the horizon usually from North toward the East, i.e. clockwise and is usually measured in degrees. It may less commonly be measured from the South point. Azimuth is often, some consider incorrectly, referred to as a bearing. ...more on Wikipedia about "Azimuth"

The celestial equator is a great circle on the imaginary celestial sphere, which is actually the plane of the terrestrial equator extended out into the universe (i.e., it could be constructed by extrapolating the Earth's equator until it touches the celestial sphere). The celestial equator is inclined by ~23.5°, with respect to the ecliptic plane; a result of axial tilt. Celestial objects near the celestial equator are visible worldwide, but they culminate the highest in the sky in the tropics. ...more on Wikipedia about "Celestial equator"

The celestial horizon, also called the rational horizon, is a great circle parallel to the horizon, the center of which is the center of the Earth. ...more on Wikipedia about "Celestial horizon"

In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of "gigantic radius", concentric and coaxial with the Earth. All objects in the sky can be thought of as lying upon the sphere. Projected, from their corresponding geographic equivalents, are the celestial equator and the celestial poles. ...more on Wikipedia about "Celestial sphere"

Circumpolar stars are those stars which are located near the celestial poles of the celestial sphere, i.e. the poles in the equatorial coordinate system. As the Earth rotates, the sky appears to rotate; and most stars will be hidden below the horizon at some point in their circular paths. If, from a certain location, a star is near enough to the celestial pole that it never appears to go "under the horizon"; it will therefore be visible (from said location) for the entire night, on every day of the year. Some of the most circumpolar stars do not seem to engage in diurnal motion, at all. ...more on Wikipedia about "Circumpolar star"

Colure, in astronomy, is either of the two principal meridians of the celestial sphere, one of which passes through the poles and the two solstices, the other through the poles and the two equinoxes; hence designated as solstitial colure and equinoxial colure, respectively. ...more on Wikipedia about "Colure"

In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Dec is comparable to latitude, projected unto the celestial sphere, and is measured in degrees north and south of the celestial equator. Therefore, points north of the celestial equator have positive declination, while those to the south have negative declination. ...more on Wikipedia about "Declination"

The ecliptic plane is the geometric plane that contains the orbit of the Earth. The ecliptic is the intersection of the ecliptic plane and the celestial sphere. A more intuitive definition would be to say that the ecliptic is the apparent path of the Sun during a year as seen from Earth. The orbits of most planets in the Solar System lie very close to it. Seen from the Earth, this is a bisecting great circle, superimposed upon the celestial sphere, which contains the different points of the Sun's path, relative to the background stars, over the course of a year. The zodiac also lies along the ecliptic plane. The ecliptic plane is inclined by ~23.5°, with respect to the celestial equator; a result of axial tilt. The orbital plane of the Moon is inclined by ~5°, with respect to the ecliptic. ...more on Wikipedia about "Ecliptic"

Ecliptic latitude is one of the co-ordinates which can be used to define the location of an astronomical object on the celestial sphere in ecliptic coordinates. In this system, the celestial sphere is divided into two hemispheres by the plane of the ecliptic, or the plane of the earth's orbit. From the perspective of the earth, the sun travels in the ecliptic and always has ecliptic latitude of 0. The ecliptic latitude is the angle north or south of the ecliptic analogous to how terrestrial latitude is the angular position on the earth north or south of the equator. The planets tend to have low ecliptic latitude; they are always within a few degrees of the ecliptic with the exception of Pluto. Most other objects in the solar system: asteroids, comets, and dust are also at low ecliptic latitude. ...more on Wikipedia about "Ecliptic latitude" shortopedia, just the best.

Ecliptic longitude is one of the co-ordinates which can be used to define the location of an astronomical object on the celestial sphere in ecliptic coordinates. In this system, the celestial sphere is divided into two hemispheres by the plane of the ecliptic. ...more on Wikipedia about "Ecliptic longitude"

Elongation is an astronomical term that refers to the angle between the Sun and a planet, as viewed from Earth. ...more on Wikipedia about "Elongation"

The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. The equator divides the planet into a Northern Hemisphere and the Southern Hemisphere. The latitude of the equator is, by definition, 0°. The length of Earth's equator is about 40,075.0 km, or 24,901.5 miles. ...more on Wikipedia about "Equator"

In astronomy, an equinox is defined as the moment when the Sun reaches one of two intersections between the celestial equator and the ecliptic. ...more on Wikipedia about "Equinox"

The fundamental plane in a spherical coordinate system is a plane which divides the sphere into two hemispheres. The latitude of a point is then the angle between the fundamental plane and the line joining the point to the centre of the sphere. ...more on Wikipedia about "Fundamental plane"

The horizon is the line that separates earth from sky. More precisely, it is the line that divides all of the directions you can possibly look into, into two categories: those which intersect the Earth, and those which do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc. The resulting intersection of earth and sky is instead known as the visible horizon. However, if you are on a ship at sea, the true horizon is strikingly apparent. Historically, the distance to the visible horizon has been extremely important as it represented the maximum range of communication and vision before the development of the radio and the telegraph. Even today, when flying an aircraft under Visual Flight Rules, a technique called attitude flying is used to control the aircraft, where the pilot uses the relationship between the aircraft's nose and the horizon to control the aircraft. He also retains his spatial orientation by referring to the horizon. ...more on Wikipedia about "Horizon"

In astronomy, the March equinox (or northward equinox) is the moment when the Sun appears to cross the celestial equator, heading northward. The March equinox is known as the vernal equinox in the Northern Hemisphere, and the autumnal equinox in the Southern Hemisphere. ...more on Wikipedia about "March equinox" Please tell your friends about http://www.shortopedia.com

In the sky, a meridian is an imaginary great circle on the celestial sphere that is perpendicular to the local horizon. It passes through the north point on the horizon, through the celestial pole, up to the zenith, and through the south point on the horizon. ...more on Wikipedia about "Meridian (astronomy)"

The nadir (from Arabic nazir, opposite) is the astronomical term for the point in the sky directly below the observer, or more precisely, the point in the sky with an altitude of -90°. ...more on Wikipedia about "Nadir"

A reference plane, in astronomy, is an arbitrary plane chosen to measure orbital elements, which are parameters needed to specify that orbit uniquely. ...more on Wikipedia about "Reference plane"

Right ascension (RA; symbol α: Greek letter alpha; celestial longitude) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination. ...more on Wikipedia about "Right ascension" http://www.shortopedia.com for you!

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