comets

Skygazing - Diurnal observation. The extreme brightness of the Sun saturates the sky and prevents the observation of less luminous objects, with the exception of the Moon, and occasionally Venus. The observation of the daytime sky can reveal some surprises nevertheless. With some additional equipment sunspots can be viewed during the day, as well as the occasional solar eclipse. It is extremely important to have the proper equipment and training when observing the sun, or you could permanently blind yourself. Never attempt to observe the sun in a telescope or binoculars w ...

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Skygazing, Skygazing - Naked eye skygazing, Skygazing - Diurnal observation, Skygazing - Nocturnal observation, Skygazing - Binocular gazing, Skygazing - Choice of binoculars, Skygazing - Advice on observational techniques, Skygazing - Observations with a refracting telescope, Skygazing - Choice of the refracting telescope, Skygazing - Advice of usage, Skygazing - The observation with a reflecting telescope, Skygazing - Types of reflecting telescope

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Neutron stars also have a maximum mass, called the Tolman-Oppenheimer-Volkoff limit. It is currently thought to be about 3 times the mass of the Sun. The exact value depends on the forces between neutrons at high density that in addition to the degenerate neutron-pressure could add to the overall pressure. If more mass accretes onto a neutron star, eventually this mass limit is reached, and new equilibriums may be found. Compact star - Strange stars. Main articlesSee also:

Compact star, Compact star - Compact stars as the endpoint of stellar evolution, Compact star - Compact stars last forever, Compact star - Thought experiment in building compact objects, Compact star - Planets, Compact star - The largest cold mass in the universe, Compact star - White dwarfs, Compact star - Neutron stars, Compact star - Exotic stars, Compact star - Strange stars, Compact star - Preon stars, Compact star - Black holes

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Quaternary geologists, paleoclimatologists, and planetary geologists specializing in meteorite and comet impacts have rejected the Tollmann bolide hypothesis as proposed by Kristan-Tollmann and Tollmann (1994). They reject his hypothesis because The evidence used to argue it can more readily explained by more mundane and less dramatic geologic processes Many of the events alleged to be associated with this impact occurred at the wrong time, sometime hundreds to thousands of years before or after his hypothesized impacts ...

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Tollmann's hypothetical bolide, Tollmann's hypothetical bolide - Mainstream Evaluation of the Tollmann Bolide Hypothesis

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When talking about celestial bodies, the center of mass has a special relevance: when a moon orbits around planet, or a planet orbits around a star, both of them are actually orbiting around their center of mass, called the barycenter, see two-body problem. The barycenter (from the Greek βαρύκεντρον) is the center of mass of two or more bodies which are orbiting each other, and is the point around which both of them orbit. It is an important concept in the fie ...

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Center of mass, Center of mass - Example, Center of mass - Comparison with center of gravity, Center of mass - Definition, Center of mass - More formulas, Center of mass - Aeronautical significance, Center of mass - Motion of the center of mass, Center of mass - Examples, Center of mass - Barycenter, Center of mass - Animations

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Travel on the surface of the ocean through the use of boats dates back to prehistoric times, but only in modern times has extensive underwater travel become possible. The deepest point in the ocean is the Mariana Trench located in the Pacific Ocean near the Northern Mariana Islands. It has a maximum depth of 10,923 m (35,838 ft) [1]. It was fully surveyed in 1951 by the British naval vesse ...

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Ocean, Ocean - Origins, Ocean - Exploration, Ocean - Climate, Ocean - Ecology, Ocean - Economy, Ocean - Ancient oceans, Ocean - Ocean rowing, Ocean - Extraterrestrial oceans

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Space dust - Airplanes. The most common way of collecting space dust is with a collector plate on a NASA airplane that flies high into the atmosphere. Dust particles attach to the plate and can be taken down to the Earth's surface for analysis. Space dust - Spacecraft. Space agencies (such as NASA) have sent space probes to collect space dust or solar wind. See also:

Space dust, Space dust - Types, Space dust - Collection methods, Space dust - Airplanes, Space dust - Spacecraft, Space dust - Terrestrial collection, Space dust - Deep-sea collection, Space dust - Analysis, Space dust - Images

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Asteroid deflection strategies - Nuclear weapons. One of the most often proposed solutions is firing nuclear missiles at the oncoming asteroid to vaporize all or most of it. While today's nuclear weapons are not powerful enough to destroy a 1 km asteroid, theoretically, thermonuclear weapons can be scaled up to any size so long as enough raw materials are available. If not completely vaporised, the resulting reduction of mass from the blast combined with the radiation blast could produce positive results. The lar ...

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Asteroid deflection strategies, Asteroid deflection strategies - Early detection, Asteroid deflection strategies - Popular strategies, Asteroid deflection strategies - Nuclear weapons, Asteroid deflection strategies - Detonating internally, Asteroid deflection strategies - Kinetic impact, Asteroid deflection strategies - Slow deflection, Asteroid deflection strategies - Other proposals, Asteroid deflection strategies - Planetary defense timeline, Asteroid deflection strategies - Formation of Moon, Asteroid deflection strategies - 3.2 billion years ago, Asteroid deflection strategies - 65 million years ago wiped out dinosaurs, Asteroid deflection strategies - 3.3 million years ago, Asteroid deflection strategies - 50000 years ago in Arizona, Asteroid deflection strategies - 1908 Tunguska event in Siberia, Asteroid deflection strategies - 1972 through Earth atmosphere, Asteroid deflection strategies - 1989 missed by 6 hours, Asteroid deflection strategies - 1991 within 1/2 the distance to Moon, Asteroid deflection strategies - 2002 within 1/3 distance to Moon, Asteroid deflection strategies - 2014 visitor, Asteroid deflection strategies - 2019 February fly by, Asteroid deflection strategies - 2029 near miss, Asteroid deflection strategies - 2085 Comet Catalina ETA, Asteroid deflection strategies - Fiction, Asteroid deflection strategies - See Fiction

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Trajectory - Uniform gravity no drag or wind. The case of uniform gravity, disregarding drag and wind, yields a trajectory which is a parabola. To model this, one chooses V = mgz, where g (gee) is the acceleration of gravity. This gives the equations of motion Simplifications are made for the sake of studying the basics. The actual situation, at least on the surface of Earth, is consi ...

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Trajectory, Trajectory - Physics of trajectories, Trajectory - Examples, Trajectory - Uniform gravity no drag or wind, Trajectory - Uphill/downhill in uniform gravity in a vacuum, Trajectory - Orbiting objects

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The Moon makes a complete orbit about once every 28 days. Each hour the Moon moves relative to the stars by an amount roughly equal to its angular diameter, or by about 0.5°. The Moon differs from most satellites of other planets in that its orbit is close to the plane of the ecliptic and not in the Earth's equatorial plane. Several ways to consider a complete orbit are detailed in the table below, but the two most familiar are: the sidereal month being the time it takes to make a complete orbit with respect to the stars, about 27.3 ...

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Moon, Moon - The two sides, Moon - Orbit, Moon - Earth & Moon, Moon - Origin and history, Moon - Physical characteristics, Moon - Composition, Moon - Selenography, Moon - Presence of water, Moon - Magnetic field, Moon - Atmosphere, Moon - Eclipses, Moon - Occultation of stars, Moon - Observation of the Moon, Moon - Exploration of the Moon, Moon - Human understanding of the Moon, Moon - Myth and folk culture, Moon - The Moon as muse, Moon - Astrology, Moon - Scientific understanding, Moon - Meteor impact on the Moon, Moon - Legal status, Moon - Satellites, Moon - Surface installations, Moon - Lunar location listings

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In December 1859, Le Verrier received a letter from a French physician and amateur astronomer called Edmond Modeste Lescarbault, who claimed to have witnessed a transit of the hypothetical planet earlier in the year. Le Verrier took the next train to the village of Orgères-en-Beauce, some 70 kilometres southwest of Paris, where Lescarbault had built himself a small observatory. Le Verrier arrived unan ...

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Vulcan planet, Vulcan planet - Argument for Vulcan's existence, Vulcan planet - The search for Vulcan, Vulcan planet - Search conclusion, Vulcan planet - Vulcan revived, Vulcan planet - Vulcan in modern fiction

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The allotropes of carbon are the different molecular configurations (allotropes) that pure carbon can take. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Several exotic allotropes have also been synthesized or discovered, including fullerenes, carbon nanotubes, lonsdaleite and aggregated diamond nanorods. In its amorphous form, carbon is essentially graphite but not held in a crystalline macrostructure. It is, rather, present as a powder which is the main constituent of substances such as charcoal, la ...

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Carbon, Carbon - Notable characteristics, Carbon - Applications, Carbon - Other uses, Carbon - History and Etymology, Carbon - Allotropes, Carbon - Occurrence, Carbon - Organic compounds, Carbon - Carbon chains, Carbon - Carbon cycle, Carbon - Isotopes, Carbon - Precautions

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Asteroid deflection strategies - Nuclear weapons. One of the most often proposed solutions is firing nuclear missiles at the oncoming asteroid to vaporize all or most of it. While today's nuclear weapons are not powerful enough to destroy a 1 km asteroid, theoretically, thermonuclear weapons can be scaled up to any size so long as enough raw materials are available. If not completely vaporised, the resulting reduction of mass from the blast combined with the radiation blast could produce positive results. The lar ...

See also:

Asteroid deflection strategies, Asteroid deflection strategies - Early detection, Asteroid deflection strategies - Popular strategies, Asteroid deflection strategies - Nuclear weapons, Asteroid deflection strategies - Detonating Internally, Asteroid deflection strategies - Kinetic impact, Asteroid deflection strategies - Slow deflection, Asteroid deflection strategies - Other proposals, Asteroid deflection strategies - Planetary Defense Timeline, Asteroid deflection strategies - 3.2 billion years ago, Asteroid deflection strategies - 65 million years ago wiped out dinosaurs, Asteroid deflection strategies - 3.3 million years ago, Asteroid deflection strategies - 5000 years ago in Arizona, Asteroid deflection strategies - 1908 Tunguska event in Siberia, Asteroid deflection strategies - 1972 through Earth atmosphere, Asteroid deflection strategies - 1989 missed by 6 hours, Asteroid deflection strategies - 1991 within 1/2 the distance to Moon, Asteroid deflection strategies - 2002 within 1/3 distance to Moon, Asteroid deflection strategies - 2014 visitor, Asteroid deflection strategies - 2019 February fly by, Asteroid deflection strategies - 2029 near miss, Asteroid deflection strategies - 2085 Comet Catalina ETA, Asteroid deflection strategies - Fiction, Asteroid deflection strategies - Fiction

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Carbon is a remarkable element for many reasons. Its different forms include one of the softest (graphite) and one of the hardest (diamond) substances known. Moreover, it has a great affinity for bonding with other small atoms, including other carbon atoms, and its small size makes it capable of forming multiple bonds. Because of these properties, carbon is known to form nearly ten million different compounds, the large majority of all chemical compounds. Carbon compounds form the basis of all life on Earth and the carbon-nitrogen cycle prov ...

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Carbon, Carbon - Notable characteristics, Carbon - Applications, Carbon - Other uses, Carbon - History and Etymology, Carbon - Allotropes, Carbon - Occurrence, Carbon - Organic compounds, Carbon - Carbon chains, Carbon - Carbon cycle, Carbon - Isotopes, Carbon - Precautions

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For a system of only two bodies that are only influenced by their mutual gravity, their orbits can be exactly calculated by Newton's laws of motion and gravity. Briefly, the sum of the forces will equal the mass times its acceleration. Gravity is proportional to mass, and falls off proportionally to the square of distance. To calculate, it is convenient to describe the motion in a coordinate system that is centered on the heavier body, and we can say ...

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Planetary orbit, Planetary orbit - History, Planetary orbit - Planetary orbits, Planetary orbit - Understanding orbits, Planetary orbit - Newton's laws of motion, Planetary orbit - Analysis of orbital motion, Planetary orbit - Orbital parameters, Planetary orbit - Orbital period, Planetary orbit - Orbital decay, Planetary orbit - Earth orbits, Planetary orbit - Scaling in gravity, Planetary orbit - Role in the evolution of atomic theory

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Astronomical spectroscopy began with Isaac Newton's initial observations of the light of the sun, dispersed by a prism. He saw a rainbow of colour, and may even have seen absorption lines. These dark bands which appear throughout the solar spectrum were first described in detail by Joseph von Fraunhofer. Most stellar spectra share these two dominant features of the sun's spectrum: emission at all wavelengths across the optical spectrum (the continuum) with ...

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Astronomical spectroscopy, Astronomical spectroscopy - Stars, Astronomical spectroscopy - Nebulae, Astronomical spectroscopy - Galaxies, Astronomical spectroscopy - Quasars, Astronomical spectroscopy - Planets and asteroids, Astronomical spectroscopy - Comets

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Retrograde motion should not be confused with retrogradation. The latter term is used in reference to the motion of the outer planets (Mars, Jupiter, Saturn, Neptune, Uranus, and Pluto). Though these planets appear to move from east to west on a nightly basis in response to the spin of Earth, they are most of the time drifting slowly eastward with respect to the background of stars, which can be observed by noting the position of these planets for several nights in a row. This motion is normal for these planets, so it is called dir ...

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Prograde and retrograde motion, Prograde and retrograde motion - Two notations, Prograde and retrograde motion - Retrograde orbits, Prograde and retrograde motion - Retrograde rotation, Prograde and retrograde motion - Retrogradation, or apparent retrograde motion, Prograde and retrograde motion - Examples, Prograde and retrograde motion - Reference

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Colonization of the outer solar system - Ceres. Ceres is one of the largest (and first) Asteroids discovered and orbits within the main Asteroid Belt. It is thought that a large percentage of the mantle of the planetoid is actually water ice [1] and it may in fact hold more water than the earth, as much as 200 million cubic kilometers. This huge reserve of water could easily be split into oxygen for air production a base and hydrogen for rocket fuel as well as powering fusion reactors in the future. Ceres would m ...

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Colonization of the outer solar system, Colonization of the outer solar system - Asteroids, Colonization of the outer solar system - Ceres, Colonization of the outer solar system - Jupiter, Colonization of the outer solar system - Europa, Colonization of the outer solar system - Ganymede, Colonization of the outer solar system - Callisto, Colonization of the outer solar system - Saturn, Colonization of the outer solar system - Titan, Colonization of the outer solar system - Uranus, Colonization of the outer solar system - Neptune, Colonization of the outer solar system - Kuiper Belt and Oort Cloud

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Moon - Composition. More than 4.5 billion years ago, the surface of the Moon was a liquid magma ocean. Scientists think that one component of lunar rocks, KREEP (K-potassium, Rare Earth Elements, and P-phosphorus), represents the last chemical remnant of that magma ocean. KREEP is actually a composite of what scientists term "incompatible elements": those which cannot fit into a crystal structure and thus were left behind, floating to the surface of the magma. For researchers, KREEP is a convenient tracer, useful ...

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Moon, Moon - The two sides of the Moon, Moon - Orbit, Moon - Earth & Moon, Moon - Tidal Effects, Moon - Double-planet hypotheses, Moon - Origin and history, Moon - Physical characteristics, Moon - Composition, Moon - Selenography, Moon - Presence of water, Moon - Magnetic field, Moon - Atmosphere, Moon - Eclipses, Moon - Occultation of stars, Moon - Observation of the Moon, Moon - Exploration of the Moon, Moon - Human understanding of the Moon, Moon - Myth and folk culture, Moon - The Moon as muse, Moon - Astrology, Moon - Scientific understanding, Moon - Meteor impact on the Moon, Moon - Legal status, Moon - Satellites, Moon - Surface installations, Moon - Lunar location listings

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Rab at Sura and Mar Samuel at Nehardea established the intellectual independence of Babylonian Jewry. Young men taking up the study of the Law there were no longer obliged to go to Palestine, since they had the foremost teachers at home. Babylon now came to be regarded, in a sense, as a second Holy Land. Samuel taught, "As it is forbidden to migrate from Palestine to Babylon, so is it forbidden to migrate from Babylon to other countries" (Ket. 111a). After Rab's death no new director was elected, and Rab's greatest pupil, R. Huna, who became ...

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Samuel of Nehardea, Samuel of Nehardea - Birth, Samuel of Nehardea - Youth, Samuel of Nehardea - His Training, Samuel of Nehardea - As Gaon, Samuel of Nehardea - His Halakha, Samuel of Nehardea - Aggadah, Samuel of Nehardea - Relations with the Persian Court, Samuel of Nehardea - Bibliography

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Apart from the Bible and the traditional Law, which were usually the only subjects of study of the Jewish youth of that time, Samuel was instructed, probably in his early youth, in other sciences. It is likely that he accompanied his father on the latter's journey to Palestine (Yet. B. M. iv. 9c; Yer. Pes. v. 32a); for after his teacher Levi ben Sisi had gone to Palestine there was no one in Babylon with whom he could have studied. According to an account in the Talmud (B. M. 85b), which Rapoport declares to be a later addition ("'Erek Milli ...

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Samuel of Nehardea, Samuel of Nehardea - Birth, Samuel of Nehardea - Youth, Samuel of Nehardea - His Training, Samuel of Nehardea - As Gaon, Samuel of Nehardea - His Halakha, Samuel of Nehardea - Aggadah, Samuel of Nehardea - Relations with the Persian Court, Samuel of Nehardea - Bibliography

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One of the remarkable achievements of Newtonian mechanics was the derivation of the laws of Kepler, in the case of the gravitational field of a single point mass (representing the Sun). The trajectory is a conic section, like an ellipse or a parabola. This agrees with the observed orbits of planets and comets, to a reasonably good approximation. Although if a comet passes close to the Sun, then it is also influenced by other forces, such as the solar wind and radiation pressure, which modify the or ...

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Trajectory, Trajectory - Physics of trajectories, Trajectory - Examples, Trajectory - Uniform gravity no drag or wind, Trajectory - Uphill/downhill in uniform gravity in a vacuum, Trajectory - Orbiting objects

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The inclination of the Moon's orbit makes it implausible that the Moon formed along with the Earth or was captured later; its origin is the subject of some scientific debate. Early speculation proposed that the Moon broke off from the Earth's crust due to centrifugal force, leaving an ocean basin (presumed to be the Pacific) behind as a scar. This concept requires too great an initial spin of the Earth and the presumption of a Pacific origin is not compatible with the geological standard model, the theory of plate tectonics. Others sp ...

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Moon, Moon - The two sides of the Moon, Moon - Orbit, Moon - Earth & Moon, Moon - Tidal Effects, Moon - Double-planet hypotheses, Moon - Origin and history, Moon - Physical characteristics, Moon - Composition, Moon - Selenography, Moon - Presence of water, Moon - Magnetic field, Moon - Atmosphere, Moon - Eclipses, Moon - Occultation of stars, Moon - Observation of the Moon, Moon - Exploration of the Moon, Moon - Human understanding of the Moon, Moon - Myth and folk culture, Moon - The Moon as muse, Moon - Astrology, Moon - Scientific understanding, Moon - Meteor impact on the Moon, Moon - Legal status, Moon - Satellites, Moon - Surface installations, Moon - Lunar location listings

Read more here: » Moon: Encyclopedia II - Moon - Origin and history