In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. These example sentences are selected automatically from various online news sources to reflect current usage of the word 'equatorial plane.' One sidereal hour (approximately 0.9973 solar hours) later, Earth's rotation will carry the star to the west of the meridian, and its hour angle will be 1h. [5]. In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time. In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. A slow motion of Earth's axis, precession, causes a slow, continuous turning of the coordinate system westward about the poles of the ecliptic, completing one circuit in about 26,000 years. The celestial equator currently passes through these constellations:[citation needed]. Setting circles in conjunction with a star chart or ephemeris allow the telescope to be easily pointed at known objects on the celestial sphere. For example, the north celestial pole has a declination of +90°. It may be implemented in spherical or rectangular coordinates. Three non-collinear points in space suffice to determine an orbital plane. Equatorial plane definition is - the plane perpendicular to the spindle of a dividing cell and midway between the poles. Commonly used reference planes and origins of longitude include: An orbital pole is either point at the ends of an imaginary line segment that runs through the center of an orbit and is perpendicular to the orbital plane. Earth-centered inertial (ECI) coordinate frames have their origins at the center of mass of Earth and do not rotate with respect to the stars. The hour angle of a point is the angle between two planes: one containing Earth's axis and the zenith, and the other containing Earth's axis and the given point. An equinox is commonly regarded as the instant of time when the plane of Earth's equator passes through the center of the Sun. Unlike right ascension, hour angle is always increasing with the rotation of Earth. Analogous to terrestrial longitude, right ascension is usually measured in sidereal hours, minutes and seconds instead of degrees, a result of the method of measuring right ascensions by timing the passage of objects across the meridian as the Earth rotates. The vernal equinox point is one of the two where the ecliptic intersects the celestial equator. The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions and orbits of Solar System objects. The ecliptic is not normally noticeable from Earth's surface because the planet's rotation carries the observer through the daily cycles of sunrise and sunset, which obscure the Sun's apparent motion against the background of stars during the year. The ECI frame is also useful for specifying the direction toward celestial objects. The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way galaxy, and the fundamental plane parallel to an approximation of the galactic plane but offset to its north. The ecliptic is the mean plane of the apparent path in the Earth's sky that the Sun follows over the course of one year; it is the basis of the ecliptic coordinate system. Declination is analogous to terrestrial latitude. In human and animal anatomy, three principal planes are used: The sagittal plane or lateral plane is a plane parallel to the sagittal suture. In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. [4]. A star's spherical coordinates are often expressed as a pair, right ascension and declination, without a distance coordinate. All have: The reference frames do not rotate with the Earth (in contrast to Earth-centred, Earth-fixed frames), remaining always directed toward the equinox, and drifting over time with the motions of precession and nutation. Although they are caused by the same effect operating over different timescales, astronomers usually make a distinction between precession, which is a steady long-term change in the axis of rotation, and nutation, which is the combined effect of similar shorter-term variations. Coordinate systems can specify an object's position in three-dimensional space or plot merely its direction on a celestial sphere, if the object's distance is unknown or trivial. The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion—are much smaller in magnitude. The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. 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 vernal equinox, and a right-handed convention. Projected onto the celestial sphere, orbital poles are similar in concept to celestial poles, but are based on the body's orbit instead of its equator. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit. On its own, the term latitude should be taken to be the geodetic latitude as defined below. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. In contrast to the common usage of spring and autumn (fall), or vernal and autumnal, equinoxes, the celestial coordinate system equinox is a direction in space rather than a moment in time. Un système de référence en anatomie, désigne la terminologie utilisée pour se repérer de façon précise dans la structure anatomique d'un organisme, humain ou non. A common example would be the positions of the centers of a massive body (host) and of an orbiting celestial body at two different times/points of its orbit. Please tell us where you read or heard it (including the quote, if possible). Briefly, geodetic latitude at a point is the angle formed by the vector perpendicular to the ellipsoidal surface from that point, and the equatorial plane. The origin for declination is the celestial equator, which is the projection of the Earth's equator onto the celestial sphere. As Earth orbits the Sun over the course of a year, the Sun appears to move with respect to the fixed stars on the celestial sphere, along a circular path called the ecliptic. The coronal plane is a plane that separates the body into anterior and posterior parts The equatorial coordinate system using spherical coordinates.The fundamental plane is formed by projection of Earth's equator onto the celestial sphere, forming the celestial equator.The primary direction is established by projecting Earth's orbit onto the celestial sphere, forming the ecliptic, and setting up the ascending node of the ecliptic on the celestial equator, forming the vernal equinox. Superimposed on this is a smaller motion of the ecliptic, and a small oscillation of the Earth's axis, nutation. Delivered to your inbox! When paired with declination, these astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system. celestial coordinate system used to specify the positions of celestial objects, timing the passage of objects across the meridian, MEASURING THE SKY A Quick Guide to the Celestial Sphere, Celestial Equatorial Coordinate Explorers. This occurs twice each year, around 20 March and 23 September. Astronomical nutation is a phenomenon which causes the orientation of the axis of rotation of a spinning astronomical object to vary over time. Here Be Dragons: A Creature Identification Quiz. Because most planets and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient. The point is defined as the center of mass of Earth, hence the term geocentric coordinates. The inclination has varied from about 22.0° to 24.5° over the past 5 million years. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the vernal (March) equinox, and it has a right-hand convention.

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