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Moid Moidelhoff
Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits of two bodies. Of greatest interest is the risk of a collision with Earth. Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are also defined with respect to other bodies as well: Jupiter MOID, Venus MOID and so on. An object is classified as a potentially hazardous object (PHO) – that is, posing a possible risk to Earth – if, among other conditions, its Earth MOID is less than 0.05 AU. For more massive bodies than Earth, there is a potentially notable close approach with a larger MOID; for instance, Jupiter MOIDs less than 1 AU are considered noteworthy since Jupiter is the most massive planet.Bruce Koehn,Minimum Orbital Intersection Distance, Lowell Observatory, retrieved o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epoch (astronomy)
In astronomy, an epoch or reference epoch is a instant, 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 Astronomical object, celestial body, as they are subject to Perturbation (astronomy), perturbations and vary with time. 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 Perihelion and aphelion, aphelion of its orbit, or the size of the major axis of its orbit. The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities. The applied tools of the disciplines of celestial mechanics or its subfield orbital mechanics (for predicting orbital paths and positions for bodies in motion under the gravitational effects of other bodi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Numbered Comets
This is a list of periodic comets that were numbered by the Minor Planet Center after having been observed on at least two occasions. Their orbital periods vary from 3.2 to 366 years. there are 499 numbered comets (1P–499P). There are 405 Jupiter-family comets (JFCs), 38 Encke-type comets (ETCs), 14 Halley-type comets (HTCs), five Chiron-type comets (CTCs), and one long-period comet ( 153P). 75 bodies are also near-Earth comets (NECs). In addition, eight numbered comets are principally classified as minor planets – five main-belt comets, two centaurs (CEN), and one Apollo asteroid – and display characteristics of both an asteroid and a comet. Occasionally, comets will break up into multiple chunks, as volatiles coming off the comet and rotational forces may cause it to break into two or more pieces. An extreme example of this is 73P/Schwassmann–Wachmann, which broke into over 50 pieces during its 1995 perihelion. List Multiples 51P/Harrington : '' back ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
162173 Ryugu
162173 Ryugu ( provisional designation ) is a near-Earth object and also a potentially hazardous asteroid of the Apollo group. It measures approximately in diameter and is a dark object of the rare spectral type Cb, with qualities of both a C-type asteroid and a B-type asteroid. In June 2018, the Japanese spacecraft '' Hayabusa2'' arrived at the asteroid. After making measurements and taking samples, ''Hayabusa2'' left Ryugu for Earth in November 2019/ and returned the sample capsule to Earth on 5 December 2020. The samples showed the presence of organic compounds, such as uracil (one of the four components in RNA) and vitamin B3. Discovery and name Ryugu was discovered on 10 May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Lab's ETS near Socorro, New Mexico, in the United States. It was given the provisional designation . The asteroid was officially named "Ryugu" by the Minor Planet Center on 28 September 2015 (). The name refers to R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
99942 Apophis
99942 Apophis ( provisional designation ) is a near-Earth asteroid and a potentially hazardous object, 450 metres (1,480 ft) by 170 metres (560 ft) in size, that caused a brief period of concern in December 2004 when initial observations indicated a probability of 0.027 (2.7%) that it would hit Earth on Friday, April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth in 2029. A small possibility nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole estimated to be 800 metres in diameter, which would have set up a future impact exactly seven years later on Easter Sunday, April 13, 2036. This possibility kept it at Level 1 on the 0 to 10 Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis's rating on the Torino scale was lowe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metre
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of a second, where the second is defined by a hyperfine transition frequency of caesium. The metre was originally defined in 1791 by the French National Assembly as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's polar circumference is approximately . In 1799, the metre was redefined in terms of a prototype metre bar. The bar used was changed in 1889, and in 1960 the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of proper length. From 1983 until 2019, the metre was formally defined as the length of the pat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Unit
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec. One au is approximately equivalent to 499 light-seconds. History of symbol usage A variety of unit symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union (IAU) had used the symbol ''A'' to denote a length equal to the astronomical unit. In the astronomical literature, the symbol AU is common. In 2006, the International Bureau of Weights and Measures (BIPM) had recommended ua as the symbol for the unit, from the French ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Diameter
Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is at least somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers, and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation. Earth has a dynamic atmosphere, which sustains Earth' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potentially Hazardous Asteroid
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the event of impact. They are conventionally defined as having a minimum orbit intersection distance with Earth of less than and an absolute magnitude of 22 or brighter, the latter of which roughly corresponds to a size larger than 140 meters. More than 99% of the known potentially hazardous objects are no impact threat over the next 100 years. , just 21 of the known potentially hazardous objects listed on the Sentry Risk Table could not be excluded as potential threats over the next hundred years. Over hundreds if not thousands of years though, the orbits of some "potentially hazardous" asteroids can evolve to live up to their namesake. Most of these objects are potentially hazardous asteroids (PHAs), and a few are comets. there are 2,304 known PHAs (about ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apollo Asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth (a > 1 AU) but perihelion distances less than the Earth's aphelion distance (q < 1.017 AU). , the number of known Apollo asteroids is 21,083, making the class the largest group of near-Earth objects (''cf''. the Aten, Amor and Atira asteroids), of which 1,742 are [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
