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Opposition (astronomy)
In positional astronomy, two astronomical objects are said to be in opposition when they are on antipodal point, opposite sides of the celestial sphere, as observed from a given body (usually Earth). A planet (or asteroid or comet) is said to be "in opposition" or "at opposition" when it is in opposition to the Sun. Because most orbits in the Solar System are nearly coplanar to the ecliptic, this occurs when the Sun, Earth, and the body are configured in an approximately straight line, or syzygy (astronomy), syzygy; that is, Earth and the body are in the same direction as seen from the Sun. Opposition occurs only for superior planets (see the diagram). The instant of opposition is defined as that when the apparent geocentric ecliptic coordinate system, celestial longitude of the body differs by 180° from the apparent geocentric longitude of the Sun. At that time, a body is: * in apparent retrograde motion * visible almost all night – rising around sunset, culmination, culmin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Positional Astronomy
Positional notation, also known as place-value notation, positional numeral system, or simply place value, usually denotes the extension to any base of the Hindu–Arabic numeral system (or decimal system). More generally, a positional system is a numeral system in which the contribution of a digit to the value of a number is the value of the digit multiplied by a factor determined by the position of the digit. In early numeral systems, such as Roman numerals, a digit has only one value: I means one, X means ten and C a hundred (however, the values may be modified when combined). In modern positional systems, such as the decimal system, the position of the digit means that its value must be multiplied by some value: in 555, the three identical symbols represent five hundreds, five tens, and five units, respectively, due to their different positions in the digit string. The Babylonian numeral system, base 60, was the first positional system to be developed, and its influence is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angular Diameter
The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual angle'', and in optics, it is the ''angular aperture'' (of a lens (optics), lens). The angular diameter can alternatively be thought of as the angular displacement through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. A person can Angular resolution, resolve with their naked eyes diameters down to about 1 arcminute (approximately 0.017° or 0.0003 radians). This corresponds to 0.3 m at a 1 km distance, or to perceiving Venus as a disk under optimal conditions. Formulation The angular diameter of a circle whose plane is perpendicular to the displacement vector between the point of view and the center of said circle can be calculated using the formula :\delta = 2\arctan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opposition Symbol
Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Comedy Central Politics * Opposition (politics), a party with views opposing those of the current government ** Loyal opposition ** Parliamentary opposition, a form of political opposition *** Leader of the Opposition Opposition parties * Opposition (Australia) * Opposition (Queensland), Australia * Ministerialists and Oppositionists (Western Australia) * Bahraini opposition * Official Opposition (Canada) * Opposition (Croatia) * Opposition Party (Hungary) * Official Opposition (India) * Opposition Front Bench (Ireland) * Opposition (Malaysia) * Opposition (Montenegro) * Official Opposition (New Zealand) * His Majesty's Most Loyal Opposition (United Kingdom) United States * Opposition Party (Northern U.S.) (1854–1858), a Northern an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Symbol
Astronomical symbols are abstract pictorial symbols used to represent astronomical objects, theoretical constructs and observational events in Western culture, European astronomy. The earliest forms of these symbols appear in Greek papyrus texts of late Classical Antiquity, antiquity. The Byzantine Empire, Byzantine codex, codices in which many Greek papyrus texts were preserved continued and extended the inventory of astronomical symbols. New symbols have been invented to represent many planets and minor planets discovered in the 18th to the 21st centuries. These symbols were once commonly used by professional astronomers, amateur astronomers, Alchemical symbol, alchemists, and astrologers. While they are still commonly used in almanacs and astrological publications, their occurrence in published research and texts on astronomy is relatively infrequent, with some exceptions such as the Sun and Earth symbols appearing in astronomical constants, and certain zodiacal signs u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Penumbral
The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object of lesser size. In cases of equal or smaller impinging objects, only an umbra and penumba are generated. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast. These phenomena are generally observed within solar systems, as the size of the stars within the system are larger than the orbiting satellites, hence these terms are most often used for the shadows cast by celestial bodies, though they are sometimes used to describe levels of darkness, such as in sunspots. Umbra The umbra () is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body. An observer within the umbra experiences a total occultation. The umbra of a round body occluding a round light source forms a right circular cone. When viewed from the cone's apex, the two bodies ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Central Lunar Eclipses
A central lunar eclipse is a lunar eclipse in which part of the Moon passes through the antisolar point, center of Earth's shadow. This type of lunar eclipse typically appears darker than other lunar eclipses. They are relatively rare in the 21st century as there only 24 of them, however they are statistically more common than non central lunar eclipses. In order for a lunar eclipse to classified as a central lunar eclipse, its Gamma (eclipse), gamma must be between -0.2725 and 0.2725. Central lunar eclipses are always total lunar eclipses and have large umbral eclipse magnitude, long duration and small value of gamma. List of central lunar eclipses 1901–1950 There were 20 central lunar eclipses in this period. 1951–2000 There were 13 central lunar eclipses in this period. 2001–2050 There are 10 central lunar eclipses in this period. 2051–2100 There will be 14 central lunar eclipses in this period. 2101-2150 There will be 21 central lunar e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Eclipse
A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to Ecliptic, the plane of the Earth's orbit. This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned (in syzygy (astronomy), syzygy) with Earth between the other two, which can happen only on the night of a full moon when the Moon is near either lunar node. The type and length of a lunar eclipse depend on the Moon's proximity to the lunar node. When the Moon is totally eclipsed by the Earth (a "deep eclipse"), "What is a deep eclipse? The smaller star is behind the bigger star" it takes on a reddish color that is caused by the planet when it completely blocks direct sunlight from reaching the Moon's surface, as the only light that is diffuse reflection, reflected from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Node
A lunar node is either of the two orbital nodes of the Moon; that is, the two points at which the orbit of the Moon intersects the ecliptic. The ''ascending'' (or ''north'') node is where the Moon moves into the northern ecliptic hemisphere, while the ''descending'' (or ''south'') node is where the Moon enters the southern ecliptic hemisphere. Motion The line of nodes, which is also the intersection between the two respective planes, rotates (precesses) with a period of 18.6 years or 19.35° per year. When viewed from the celestial north, the nodes move clockwise around Earth, I.e. with a retrograde motion (opposite to Earth's own spin and its revolution around the Sun). So the time from one node crossing to the next (see eclipse season) is approximately a half-year minus half of 19.1 days -- or about 173 days. Because the orbital plane of the Moon precesses in space, the lunar nodes also precess around the ecliptic, completing one revolution (called a ''draconic period' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the Equator, the plane of the satellite's orbit is the same as the Earth's equatorial plane, and the satellite's orbital inclination is 0°. The general case for a circular orbit is that it is tilted, spending half an orbit over the northern hemisphere and half over the southern. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°. Orbits The inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the orbital plane and the plane of reference, normally stated in degrees. For a satellite orbiting a planet, the plane of reference is usually the plane containing the planet's equator. For pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moon
The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar day) that is synchronized to its orbital period (Lunar month#Synodic month, lunar month) of 29.5 Earth days. This is the product of Earth's gravitation having tidal forces, tidally pulled on the Moon until one part of it stopped rotating away from the near side of the Moon, near side, making always the same lunar surface face Earth. Conversley, the gravitational pull of the Moon, on Earth, is the main driver of Earth's tides. In geophysical definition of planet, geophysical terms, the Moon is a planetary-mass object or satellite planet. Its mass is 1.2% that of the Earth, and its diameter is , roughly one-quarter of Earth's (about as wide as the contiguous United States). Within the Solar System, it is the List of Solar System objects by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opposition Surge
The opposition surge (sometimes known as the opposition effect, opposition spike or Seeliger effect) is the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer. The term is most widely used in astronomy, where generally it refers to the sudden noticeable increase in the brightness of a celestial body such as a planet, moon, or comet as its phase angle of observation approaches zero. It is so named because the reflected light from the Moon and Mars appear significantly brighter than predicted by simple Lambertian reflectance when at astronomical opposition. Two physical mechanisms have been proposed for this observational phenomenon: shadow hiding and coherent backscatter. Overview The phase angle is defined as the angle between the observer, the observed object and the source of light. In the case of the Solar System, the light source is the Sun, and the observer is generally on Earth. At zero phase angle, the S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
