comets

The classical "Big Five" mass extinctions identified by Raup and Sepkoski (1982) are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous. These and a selection of other extinction events are highlighted below: 488 million years ago — a series of mass extinctions at the Cambrian-Ordovician transition (the Cambrian-Ordovician extinction events) eliminated many brachiopods and conodonts and severely reduced the number of trilobite species. See also:

Extinction event, Extinction event - Extinction events, Extinction event - Causes for Mass Extinction, Extinction event - Postulated extinction cycles

Read more here: » Extinction event: Encyclopedia II - Extinction event - Extinction events

According to the IAU, apart from a limited number of bright stars with historic names, stars do not have proper names. Where historic names exist, these names are, with a few exceptions, taken from the Arabic language: this reflects the leading role of Arab culture in astronomy while Europe was experiencing the Middle Ages. See List of traditional star names for a list of some of these names. There are no more than a few thousand stars that appear sufficiently bright in the Earth's sky to be visible to the naked eye, so this represent ...

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Astronomical naming conventions, Astronomical naming conventions - Names of stars, Astronomical naming conventions - Managing the initialisms of star catalogues, Astronomical naming conventions - Names and boundaries of constellations, Astronomical naming conventions - Names of galaxies, Astronomical naming conventions - Names of planets, Astronomical naming conventions - Natural satellites of planets, Astronomical naming conventions - Geological and geographical features on planets and satellites, Astronomical naming conventions - Minor planets, Astronomical naming conventions - Comets, Astronomical naming conventions - Designations for extra-solar planets

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Mar Samuel was very modest in his associations with others, openly honoring any one from whom he had gained any knowledge (Baba Metzia 33a). He never obstinately insisted on his own opinion, but yielded as soon as he was convinced of being in error ('Eruvin 90a, b; Ḥul. 76b; Ber. 36a). He was friendly to all men, and declared: "It is forbidden to deceive any man, be he Jew or pagan" (Ḥul. 94a). "Before the throne of the Creator there is no difference between Jews and pagans, since there are many noble and virtuous among the latter" (Yer. ...

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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

Read more here: » Samuel of Nehardea: Encyclopedia II - Samuel of Nehardea - His Halakha

Until a large portion of the galaxy is surveyed for signs of life or contact is made with other civilizations, the panspermia hypothesis in its fullest meaning will remain difficult to test. There is, however, circumstantial evidence for exogenesis: Panspermia - Narrow time window for geogenesis. The Precambrian fossil record indicates that life appeared soon after the Earth was formed. Unless the Earth just happened to be the site of a large number of fortuitous coincidences, this would imply that life ap ...

See also:

Panspermia, Panspermia - The panspermia theory, Panspermia - Evidence, Panspermia - Narrow time window for geogenesis, Panspermia - Extremophiles, Panspermia - Wider range of potential habitats for life, Panspermia - Evidence of extraterrestrial life, Panspermia - Objections to panspermia and exogenesis, Panspermia - Directed panspermia, Panspermia - Science fiction

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Technology has now advanced to a level where humans are capable to inventory the NEO population. Given the catastrophic consequences of a collision with a large object, the NEO Obersvations Program (NEOO) is a result of a 1998 congressional directive to NASA to begin a program to identify 1 kilometer or larger objects to around 90 percent confidence level or better. Catalina Sky Survey - Other Reasons. In addition to surveying how many NEOs there are, there are other benefits to this project. For example, ...

See also:

Catalina Sky Survey, Catalina Sky Survey - Assessment of the Threat, Catalina Sky Survey - Other Reasons, Catalina Sky Survey - Mission Goal, Catalina Sky Survey - Survey Information, Catalina Sky Survey - CSS/SSS Team

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Orbiter is a first-person perspective space flight simulator. It is function-oriented, with the interface focused on maneuvering the spacecraft, rather than perspective-oriented, as in Celestia. Orbiter allows any user to explore the solar system on a number of spacecraft, both realistic, such as the Space Shuttle Atlantis, and fictional, such as the Delta-glider. Orbiter contains the realism necessary to re-enact historical space flights while the ability to fly more futuristic ships allows the player to make timely travel aro ...

See also:

Orbiter sim, Orbiter sim - About the simulator, Orbiter sim - Included spacecraft, Orbiter sim - Orbiter add-ons, Orbiter sim - Reviews

Read more here: » Orbiter sim: Encyclopedia II - Orbiter sim - About the simulator

Modern computer simulations show the Kuiper belt to have been formed by Jupiter, with the considerable gravity of the young Jupiter ejecting smaller bodies which didn't all escape completely, and also having been formed in-situ. The same simulations and other theories predict there should be bodies of significant mass in the belt, Mars-sized or Earth-sized. The first astronomers to suggest the existence of this belt were Frederick C. Leonard in 1930 and Kenneth E. Edgeworth in 1943. In 1951 Gerard Kuiper suggested that the belt was th ...

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Kuiper belt, Kuiper belt - Origins, Kuiper belt - Name, Kuiper belt - Kuiper belt objects, Kuiper belt - Discoveries thus far, Kuiper belt - Orbital trajectories, Kuiper belt - Term kuiper belt object, Kuiper belt - Largest KBOs

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According to their location, the objects in the solar system are divided into three zones: Zone I or the inner solar system, including terrestrial planets and the Main belt of asteroids; Zone II, including the giant planets, their satellites and the centaurs, and Zone III, or the outer solar system, comprising the area of the Trans-Neptunian objects including the Kuiper Belt, the Oort cloud, and the vast region in between.

See also:

Solar system, Solar system - Structure and layout of the solar system, Solar system - Origin and age of the solar system, Solar system - Regions of the solar system, Solar system - Interplanetary medium, Solar system - The inner planets, Solar system - The asteroid belt, Solar system - The outer planets, Solar system - The trans-Neptunian region, Solar system - And beyond, Solar system - Galactic orbit of the solar system, Solar system - Planetary system formation, Solar system - Discovery of the solar system, Solar system - Exploration of the solar system, Solar system - Attributes of major planets, Solar system - Attributes of the largest minor planets, Solar system - Other facts

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The overwhelming majority of asteroids have orbits lying between the orbits of Mars and Jupiter, roughly between 2 to 4 AU. These couldn't form a planet due to the gravitational influence of Jupiter. Jupiter's gravitational influence, through orbital resonance, clears Kirkwood gaps in the asteroid belt, first recognised by Daniel Kirkwood in 1874. The region with the densest concentration (lying between the Kirkwood gaps at 2.06 and 3.27 AU, with eccentricities below about 0.3, and inclinations smaller than 30°) is often called the M ...

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Minor planet, Minor planet - Groups out to the orbit of Earth, Minor planet - Groups out to the orbit of Mars, Minor planet - The main asteroid belt, Minor planet - Families within the main asteroid belt, Minor planet - Other groups out to the orbit of Jupiter, Minor planet - Groups beyond the orbit of Jupiter, Minor planet - Quasi-satellites and horseshoe objects

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Sitchin has recently put forth his own date for the next passage of Nibiru in the year 2085, but the date most talked about is 2012 which marks the end of the Maya calendar. Nibiru (the planet associated with Marduk in Babylonian cosmology) is a central element of Sitchin's theory. He claims it was a tenth planet (twelfth to those who included the Sun and Moon) which followed a long, elliptical orbit, reac ...

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Zecharia Sitchin, Zecharia Sitchin - Theories, Zecharia Sitchin - Tiamat Planet Theory, Zecharia Sitchin - Annunaki, Zecharia Sitchin - Enki, Zecharia Sitchin - Anu, Zecharia Sitchin - Works

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Abenaki mythology - Gluskab and Malsumis. Tabaldak, the creator god, made humans and then Gluskab (several variants of whom were associated with different branches of the Abenaki, including Glooscap, Glooskap, Gluskabe Klooskomba, Nanabozho) and Malsumis sprang from the dust on his hand. Gluskab and Malsumis both had the power to create a good world, but only Gluskab did so. Malsumis still seeks evil to this day. Gluskab founded the Golden Age of the Earth by rendering the evil spirits of the Ancient Age s ...

See also:

Abenaki mythology, Abenaki mythology - Beings of the Golden Age, Abenaki mythology - Gluskab and Malsumis, Abenaki mythology - Beings of the Present Age, Abenaki mythology - External link

Read more here: » Abenaki mythology: Encyclopedia II - Abenaki mythology - Beings of the Golden Age

-logy - A. Acarology, the study of ticks and mites Acridilogy, the study of Grasshoppers and Locusts Actinobiology, the study of the effects of radiation upon living organisms Actinology, the study of the effect of light on chemicals Aerobiology, a branch of biology that studies organic particles, such as bacteria, fungal spores, very small insects and pollen, which are passively transported by the air. Aerology, the study of the free atmosphereSee also:

-logy, -logy - Etymology, -logy - Other words ending in ology, -logy - Usage, -logy - List of -ologies, -logy - A, -logy - B, -logy - C, -logy - D, -logy - E, -logy - F, -logy - G, -logy - H, -logy - I, -logy - J, -logy - K, -logy - L, -logy - M, -logy - N, -logy - O, -logy - P, -logy - R, -logy - S, -logy - T, -logy - U, -logy - V, -logy - X, -logy - Z, -logy - Ologies that are not fields of study

Read more here: » -logy: Encyclopedia II - -logy - List of -ologies

-logy - A. Acarology, the study of ticks and mites Acridilogy, the study of Grasshoppers and Locusts Actinobiology, the study of the effects of radiation upon living organisms Actinology, the study of the effect of light on chemicals Aerobiology, a branch of biology that studies organic particles, such as bacteria, fungal spores, very small insects and pollen, which are passively transported by the air. Aerology, the study of the free ...

See also:

-logy, -logy - Etymology, -logy - Other words ending in ology, -logy - Usage, -logy - List of -ologies, -logy - A, -logy - B, -logy - C, -logy - D, -logy - E, -logy - F, -logy - G, -logy - H, -logy - I, -logy - J, -logy - K, -logy - L, -logy - M, -logy - N, -logy - O, -logy - P, -logy - R, -logy - S, -logy - T, -logy - U, -logy - V, -logy - X, -logy - Z, -logy - Ologies that are not fields of study

Read more here: » -logy: Encyclopedia II - -logy - List of -ologies

The Moon makes a complete orbit about the Earth approximately 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 t ...

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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 - Orbit

In stellar and galactic astronomy, the standard distance is 10 parsecs (about 32.616 light years, or 3×1014 kilometres). A star at ten parsecs has a parallax of 0.1" (100 milli arc seconds). In defining absolute magnitude it is necessary to specify the type of electromagnetic radiation being measured. When referring to total energy output, the proper term is bolometric magnitude. The dimmer an object (at a distance of 10 parsecs) would appear, the higher its absolute magnitude. The lower an object's absolute magnitude, the higher its lumin ...

See also:

Absolute magnitude, Absolute magnitude - Absolute Magnitude for stars and galaxies M, Absolute magnitude - Computation, Absolute magnitude - Apparent magnitude, Absolute magnitude - Absolute Magnitude for planets H, Absolute magnitude - Calculations, Absolute magnitude - Apparent magnitude

Read more here: » Absolute magnitude: Encyclopedia II - Absolute magnitude - Absolute Magnitude for stars and galaxies M

Lowell Observatory Near-Earth-Object Search - May 20 2004. LONEOS Discoveres Asteroid with the Smallest Orbit MPC Electronic Circular Announcement Orbit Diagram(PDF) Lowell Observatory Near-Earth-Object Search - October 15 2003. Recovery of 1937 UB (Hermes) Recovery images of 1937 UB (Hermes) Orbit Diagram Documentation of Hermes' Recovery Lowell Observatory Near-Earth-Object Search - October 3 2003. Discovery of the closest Eart ...

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Lowell Observatory Near-Earth-Object Search, Lowell Observatory Near-Earth-Object Search - Telescope, Lowell Observatory Near-Earth-Object Search - CCD camera, Lowell Observatory Near-Earth-Object Search - Camera management, Lowell Observatory Near-Earth-Object Search - Computers, Lowell Observatory Near-Earth-Object Search - Software, Lowell Observatory Near-Earth-Object Search - Observing site, Lowell Observatory Near-Earth-Object Search - The LONEOS dome, Lowell Observatory Near-Earth-Object Search - Press releases, Lowell Observatory Near-Earth-Object Search - May 20 2004, Lowell Observatory Near-Earth-Object Search - October 15 2003, Lowell Observatory Near-Earth-Object Search - October 3 2003, Lowell Observatory Near-Earth-Object Search - August 14 2001, Lowell Observatory Near-Earth-Object Search - LONEOS scientific staff

Read more here: » Lowell Observatory Near-Earth-Object Search: Encyclopedia II - Lowell Observatory Near-Earth-Object Search - Press releases

Amorphous ice - Low-density amorphous ice. Low-density amorphous ice (also called LDA, vapor-deposited amorphous water ice, amorphous solid water) is usually formed in the laboratory by a slow accumulation of water vapor molecules (physical vapor deposition) onto a very smooth metal crystal surface under 120 K. In outer space it is expected to be formed in a similar manner on a variety of cold substrates, such as dust particles. It is expected to be common in the subsurface of exterior planets, and comets ^{See also:}

Amorphous ice, Amorphous ice - Formation techniques, Amorphous ice - Forms, Amorphous ice - Low-density amorphous ice, Amorphous ice - High-density amorphous ice, Amorphous ice - Very-high-density amorphous ice, Amorphous ice - Hyperquenched glassy water, Amorphous ice - Uses

Read more here: » Amorphous ice: Encyclopedia II - Amorphous ice - Forms

NEAR Shoemaker - Summary. The primary goal of the mission was to study the near Earth asteroid 433 Eros from orbit for approximately one year. Eros is an S-type asteroid approximately 13 × 13 × 33 km in size, the second largest near-Earth asteroid. Initially the orbit was circular with a radius of 200 km. The radius of the orbit was brought down in stages to a 50 × 50 km orbit on 30 April 2000 and decreased to 35 × 35 km on July 14, 2000. The orbit was raised over succeeding months to a 200 × 200 km orbit an ...

See also:

NEAR Shoemaker, NEAR Shoemaker - Mission profile, NEAR Shoemaker - Summary, NEAR Shoemaker - The journey to Eros, NEAR Shoemaker - Failure of first attempt at orbital insertion, NEAR Shoemaker - Orbital insertion, NEAR Shoemaker - Orbits and landing, NEAR Shoemaker - Spacecraft and subsystems, NEAR Shoemaker - Reference

Read more here: » NEAR Shoemaker: Encyclopedia II - NEAR Shoemaker - Mission profile

There are a many ways for people to become involved in amateur astronomy and study the night sky. One option is to join a local astronomical society, the members of which will often be very happy to help a newcomer take a more active part. Some people also prefer to simply teach themselves, in which case there are likely to be a large amount of books in the local library. Common objects that are observed early are the Moon and planets. Another thing that most newcomers to amateur astronomy become acquainted with are the more prominent ...

See also:

Amateur astronomy, Amateur astronomy - Amateur astronomy and scientific research, Amateur astronomy - Societies for amateur astronomy, Amateur astronomy - Approaches to using amateur telescopes, Amateur astronomy - Star hopping, Amateur astronomy - GOTO telescopes, Amateur astronomy - Comparing methodologies, Amateur astronomy - Additional tools and activities, Amateur astronomy - Beginning in amateur astronomy, Amateur astronomy - Beginning with a GOTO telescope, Amateur astronomy - Becoming acquainted with the night sky, Amateur astronomy - Suggested reading

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Cysat's most important work was on comets, and he observed the comet of 1618. He published a monograph on the comet called Mathematica astronomica de loco, motu, magnitudine et causis cometae qui sub finem anni 1618 et initium anni 1619 in coelo fulsit. Ingolstadt Ex Typographeo Ederiano 1619 (Ingolstadt, 1619). According to Cysat’s opinion, comets circled around the sun, and he demonstrated at the same time that the orbit of the comet was parabolic, not circular. Cysat’s observ ...

See also:

Johann Baptist Cysat, Johann Baptist Cysat - Cysat and Comets, Johann Baptist Cysat - Other work, Johann Baptist Cysat - Sources

Read more here: » Johann Baptist Cysat: Encyclopedia II - Johann Baptist Cysat - Cysat and Comets

Viewed from near Alpha Centauri, the sky (other than the Alpha Centauri stars) would appear very much as it does to observers on Earth, with most of the constellations such as Ursa Major and Orion being almost unchanged. However, Centaurus would be missing its brightest star and our Sun would appear as a 0.5-magnitude star in Cassiopeia. Roughly speaking, the \/\/ of Cassiopeia would become a /\/\/, with the Sun at the leftmost end, closest to ε Cassiopeiae. The position can easily be plotted as RA 02h39m35s, dec +6 ...

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Alpha Centauri, Alpha Centauri - Names, Alpha Centauri - System components, Alpha Centauri - Possibility of planet formation, Alpha Centauri - Sky appearance from Alpha Centauri, Alpha Centauri - Apparent movement, Alpha Centauri - Alpha Centauri in fiction

Read more here: » Alpha Centauri: Encyclopedia II - Alpha Centauri - Sky appearance from Alpha Centauri

The Sun is a near-perfect sphere, with an oblateness estimated at about 9 millionths, which means the polar diameter differs from the equatorial by about 10 km. This is because the centrifugal effect of the Sun's slow rotation is 18 million times weaker than its surface gravity (at the equator). Tidal effects from the planets do not significantly affect the shape of the Sun, although the Sun itself orbits the center of mass of the solar system, which is offset from the Sun's center mostly because of the large mass of Jupiter. The mass of the Sun is so comparatively great that the center of mass of the solar system is generally wit ...

See also:

Sun, Sun - General information, Sun - Structure, Sun - Core, Sun - Radiation zone, Sun - Convection zone, Sun - Photosphere, Sun - Temperature minimum, Sun - Chromosphere, Sun - Corona, Sun - Theoretical problems, Sun - Solar neutrino problem, Sun - Coronal heating problem, Sun - Faint young sun problem, Sun - Magnetic field, Sun - Position of the Sun through the year, Sun - Solar space missions, Sun - History and future of the Sun, Sun - Human understanding of the Sun, Sun - The Sun as a power source, Sun - Sun and eye damage

Read more here: » Sun: Encyclopedia II - Sun - Structure