Equinox (celestial coordinates)In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. Although there are two such intersections, the equinox associated with the Sun's ascending node is used as the conventional origin of celestial coordinate systems and referred to simply as "the equinox".
March equinoxThe March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox (or spring equinox) in the Northern Hemisphere and as the autumnal equinox in the Southern Hemisphere. On the Gregorian calendar at 0° longitude, the northward equinox usually occurs on March 20.
Aries (constellation)Aries is one of the constellations of the zodiac. It is located in the Northern celestial hemisphere between Pisces to the west and Taurus to the east. The name Aries is Latin for ram. Its traditional astrological symbol is (♈︎). It is one of the 48 constellations described by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.
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.
EclipticThe ecliptic or ecliptic plane is the apparent path of the Sun on the celestial sphere, resulting from Earth's orbit around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. The ecliptic is so named because the ancients noted that eclipses only occur when the Moon is crossing it.
ConstellationA constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellations were likely defined in prehistory. People used them to relate stories of their beliefs, experiences, creation, and mythology.
Axial precessionIn astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particular, Earth's axial precession is the gradual shift in the orientation of Earth's axis of rotation.
Celestial sphereIn astronomy and navigation, the celestial sphere is an abstractsphere 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 hemisphericalscreen over the observing location.
EquinoxA solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun rises exactly in the east and sets exactly in the west. This occurs twice each year, around 20 March and 23 September. An equinox is defined as the time when the plane of Earth's equator passes through the geometric center of the Sun's disk.
Spring (season)Spring, also known as springtime, is one of the four temperateseasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa.
AutumnAutumn, also known as fall in North American English, is one of the four temperateseasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, beginning in September (Northern Hemisphere) or March (Southern Hemisphere). Autumn is the season when the duration of daytime becomes noticeably shorter and the temperature cools considerably.
Astronomical coordinate systemsIn astronomy, coordinate systems are used for specifying positions of celestial objects (satellites, planets, stars, galaxies, etc.) relative to a given reference frame, based on physical reference points available to a situated observer (e.g. the true horizon and north to an observer on Earth's surface).*As an Amazon Associate I earn from qualifying purchases.