comets - Article Index

Encyclopedia - Celestial Mechanics: Encyclopedia - Celestial Mechanics
Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. The field applies...   » Read the article

Encyclopedia - Georges-louis Leclerc, Comte De Buffon: Encyclopedia - Georges-louis Leclerc, Comte De Buffon
Georges-Louis Leclerc, Comte de Buffon (September 7, 1707 – April 16, 1788) was a French naturalist, mathematician, biologist, cosmolog...   » Read the article

Encyclopedia - Astronomical Spectroscopy: Encyclopedia - Astronomical Spectroscopy
Astronomical spectroscopy is the technique of spectroscopy used in astronomy. As spectroscopy is described in its own article, this artic...   » Read the article

Encyclopedia - Astronomical Naming Conventions: Encyclopedia - Astronomical Naming Conventions
In ancient times, only the Sun and Moon, a few hundred stars and the most easily visible planets had names. Over the last few hundred yea...   » Read the article

Encyclopedia - Center Of Mass: Encyclopedia - Center Of Mass
The center of mass of an object is a point at which the object's mass can be assumed, for many purposes, to be concentrated. Center of m...   » Read the article

Encyclopedia - Alexis Clairault: Encyclopedia - Alexis Clairault
Alexis Claude Clairault (or Clairaut) (May 3, 1713 – May 17, 1765) was a French mathematician. He was born in Paris, France, where his ...   » Read the article

Encyclopedia - Brian G. Marsden: Encyclopedia - Brian G. Marsden
Brian G. Marsden is a British astronomer, the longtime director of the Minor Planet Center. He specializes in celestial mechanics and ast...   » Read the article

Encyclopedia - Benjamin Apthorp Gould: Encyclopedia - Benjamin Apthorp Gould
Benjamin Apthorp Gould (September 27, 1824 – November 26, 1896) was an American astronomer. He was born in Boston, Massachusetts. Havin...   » Read the article

Encyclopedia - Astrodynamics: Encyclopedia - Astrodynamics
Astrodynamics is the study of the motion of rockets, missiles, and space vehicles, as determined from Sir Isaac Newton's laws of motion a...   » Read the article

Encyclopedia - Minor Planet: Encyclopedia - Minor Planet
Minor planets, or planetoids are minor bodies of the Solar system orbiting the Sun (or of other planetary systems orbiting other stars) t...   » Read the article

Encyclopedia - Algol: Encyclopedia - Algol
Algol (β Per / Beta Persei) is a bright star in the constellation Perseus. It is one of the best known eclipsing binaries, the first suc...   » Read the article

Encyclopedia - Alpha Centauri: Encyclopedia - Alpha Centauri
Alpha Centauri (α Cen / α Centauri) is the brightest star system (a triple star system) in the southern constellation of Centaurus, and...   » Read the article

Encyclopedia - Alexis Bouvard: Encyclopedia - Alexis Bouvard
Alexis Bouvard (June 27, 1767 – June 7, 1843) was a French astronomer, born in Contamines, France. Bouvard's achievements included the ...   » Read the article

Encyclopedia - Amorphous Ice: Encyclopedia - Amorphous Ice
Everyday ice is a crystal, which means its molecules are lined up in a repeating pattern. Amorphous ice is an amorphous solid form of wat...   » Read the article

Encyclopedia - Anders Johan Lexell: Encyclopedia - Anders Johan Lexell
Anders Johan Lexell (December 24, 1740 – December 11, 1784 (Julian calendar: November 30)) was a Swedish-Russian astronomer and mathema...   » Read the article

Encyclopedia - Amateur Astronomy: Encyclopedia - Amateur Astronomy
Amateur astronomy, often called back yard astronomy, is a hobby whose participants enjoy observing celestial objects. It is usually assoc...   » Read the article

Encyclopedia - William Herschel: Encyclopedia - William Herschel
Sir Wilhelm Friedrich Herschel, FRS (Hanover, November 15, 1738 – August 25, 1822 Slough, then in Buckinghamshire now in Berkshire) was...   » Read the article

Encyclopedia - Water Molecule: Encyclopedia - Water Molecule
Water has the chemical formula H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. It is in dy...   » Read the article

Encyclopedia - Water Vapor: Encyclopedia - Water Vapor
Water vapor or water vapour, also aqueous vapour, is the gas phase of water. On the Earth, water vapor is one state of the water cycle wi...   » Read the article

Encyclopedia - Coronagraph: Encyclopedia - Coronagraph
A coronagraph is a telescopic attachment designed specifically to block out the harsh, direct light from a star, so that nearby objects c...   » Read the article

Encyclopedia - Cosmic Dust: Encyclopedia - Cosmic Dust
Cosmic dust - Introductory Material. Cosmic Dust refers to particles in space which are assemblages of a few molecules to tenth-millime...   » Read the article

Encyclopedia - Damocloid Asteroid: Encyclopedia - Damocloid Asteroid
Damocloids are asteroids such as 5335 Damocles and 1996 PW that have Halley family or long-period highly eccentric orbits typical of peri...   » Read the article

Encyclopedia - Cretaceous-tertiary Extinction Event: Encyclopedia - Cretaceous-tertiary Extinction Event
The Cretaceous-Tertiary (K-T or KT) extinction event, also known as the KT boundary, was a period of massive extinction of species, about...   » Read the article

Encyclopedia - Compact Star: Encyclopedia - Compact Star
In astronomy, a compact star (sometimes called a compact object) is a star that is a white dwarf, a neutron star, an exotic star, or a bl...   » Read the article

Encyclopedia - Colonization Of The Outer Solar System: Encyclopedia - Colonization Of The Outer Solar System
Some of the moons of the outer planets of the solar system are large enough to be suitable places for colonization. Many of the larger mo...   » Read the article

Encyclopedia - Centaur Planetoid: Encyclopedia - Centaur Planetoid
The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. The...   » Read the article

Encyclopedia - Charge Heraldry: Encyclopedia - Charge Heraldry
In heraldry, a charge is the image that occupies the field on an escutcheon (or shield). The most common charges, or "ordinaries", are ge...   » Read the article

Encyclopedia - Adrien Auzout: Encyclopedia - Adrien Auzout
Adrien Auzout (January 28th, 1622–May 23rd, 1691) was a French astronomer. He was born in Rouen, France, the son of a clerk in the cour...   » Read the article

Encyclopedia - Vulcanoid Asteroid: Encyclopedia - Vulcanoid Asteroid
Vulcanoids are hypothetical asteroids that may orbit in a dynamically stable zone between 0.08 and 0.21 astronomical units from the Sun, ...   » Read the article

Encyclopedia - Carbon: Encyclopedia - Carbon
Carbon is a chemical element in the periodic table that has the symbol C and atomic number 6. An abundant nonmetallic, tetravalent eleme...   » Read the article

Encyclopedia - Archaeoastronomy: Encyclopedia - Archaeoastronomy
Archaeoastronomy (also spelled Archeoastronomy) is the study of astronomy in its cultural context, drawing on archaeological and anthropo...   » Read the article

Encyclopedia - Georges-louis Leclerc Comte De Buffon: Encyclopedia - Georges-louis Leclerc Comte De Buffon
Georges-Louis Leclerc, Comte de Buffon (September 7, 1707 – April 16, 1788) was a French naturalist, mathematician, biologist, cosmolog...   » Read the article

Encyclopedia - Disaster: Encyclopedia - Disaster
A disaster (from Latin meaning, "bad star") is the impact of a natural or man-made event that negatively affects life, property, liveliho...   » Read the article

Encyclopedia - Planet: Encyclopedia - Planet
A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star that is not a star itself. The n...   » Read the article

Encyclopedia - Panspermia: Encyclopedia - Panspermia
Panspermia is the hypothesis that the seeds of life are ubiquitous in the universe, that they may have delivered life to Earth, and that ...   » Read the article

Encyclopedia - Astronomy: Encyclopedia - Astronomy
Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally, "law of the stars") is the sc...   » Read the article

Encyclopedia - Dust: Encyclopedia - Dust
Dust is a general name for minute solid particles of diameters less than 500 micrometers (otherwise see sand or granulates) and, more gen...   » Read the article

Encyclopedia - Planetary Orbit: Encyclopedia - Planetary Orbit
In physics, an orbit is the path that an object makes around another object while under the influence of a source of centripetal force, s...   » Read the article

Encyclopedia - Ocean: Encyclopedia - Ocean
Ocean (from Okeanos, Greek for river, the ancient Greeks noticed that a strong current flowed off Gibraltar, and assumed it was a great r...   » Read the article

Encyclopedia - Muspelheim: Encyclopedia - Muspelheim
Muspelheim ("Flameland"), also called Muspel (Old Norse Múspellsheimr and Múspell, respectively), is the realm of fire in Norse Mytholo...   » Read the article

Encyclopedia - Ephemeris: Encyclopedia - Ephemeris
Wikisource has ephemerides of several planets: Ephemeris of Sun Ephemeris of Moon Ephemeris of Mercury Ephemeris of Venus Ephemeris of M...   » Read the article

Encyclopedia - Prograde And Retrograde Motion: Encyclopedia - Prograde And Retrograde Motion
Prograde motion is the rotational or orbital motion of a body in a direction similar to that of other bodies within a given system, and i...   » Read the article

Encyclopedia - Moon: Encyclopedia - Moon
The Moon as seen from Earth Ammonia Carbon dioxide The Moon is the planet Earth's only natural satellite. It has no formal name other tha...   » Read the article

Encyclopedia - Sun: Encyclopedia - Sun
(332,950 Earths) (27.9 g) The Sun (or Sol) is the star at the center of our Solar system. Earth orbits the Sun, as do many other bodies, ...   » Read the article

Encyclopedia - Zecharia Sitchin: Encyclopedia - Zecharia Sitchin
Zecharia Sitchin was born in Russia and raised in Palestine, where he acquired a knowledge of modern and ancient Hebrew, other Semitic an...   » Read the article

Encyclopedia - -logy: Encyclopedia - -logy
The English suffix -ology or -logy denotes a field of study or academic discipline, and -ologist describes a person who studies that fiel...   » Read the article

Encyclopedia - Abenaki Mythology: Encyclopedia - Abenaki Mythology
The Abenaki (also Wabanaki) are a Native American tribe located in the northeastern United States. Religious ceremonies are led by shaman...   » Read the article

Encyclopedia - Absolute Magnitude: Encyclopedia - Absolute Magnitude
In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away fro...   » Read the article

Encyclopedia - Solar System: Encyclopedia - Solar System
The solar system comprises our Sun and the retinue of celestial objects gravitationally bound to it. Traditionally, this is said to consi...   » Read the article

Encyclopedia - Torino Scale: Encyclopedia Ii - Torino Scale - Overview
The Torino Scale uses a scale from 0 to 10. A 0 indicates an object has a negligibly small chance of collision with the Earth, compared w...   » Read the article

Encyclopedia - Trajectory: Encyclopedia Ii - Trajectory - Examples
Trajectory - Uniform gravity no drag or wind. The case of uniform gravity, disregarding drag and wind, yields a trajectory which is a p...   » Read the article

Encyclopedia - Elliptic Orbit: Encyclopedia Ii - Elliptic Orbit - Velocity
Under standard assumptions the orbital velocity () of a body traveling along elliptic orbit can be computed as: where: is standard g...   » Read the article

Encyclopedia - Impact Event: Encyclopedia Ii - Impact Event - Mass Extinctions And Impacts
In the past 600 million years there have been five major mass extinctions that on average extinguished half of all species. The largest m...   » Read the article

Encyclopedia - Ethane: Encyclopedia Ii - Ethane - Ocurrence And Use
After methane, ethane is the second-largest component of natural gas. Natural gas from different gas fields varies in ethane content from...   » Read the article

Encyclopedia - Extrasolar Planet: Encyclopedia Ii - Extrasolar Planet - Methods Of Detection
There are currently six methods of detecting extrasolar planets which are too faint relative to their much brighter host stars to be dire...   » Read the article

Encyclopedia - Colonization Of The Outer Solar System: Encyclopedia Ii - Colonization Of The Outer Solar System - Jupiter
Colonization of the outer solar system - Europa. The Artemis Project designed a plan to colonize Europa. Scientists were to inhabit igl...   » Read the article

Encyclopedia - Roche Limit: Encyclopedia Ii - Roche Limit - Determining The Roche Limit
The Roche limit depends on the rigidity of the satellite. At one extreme, a rigid satellite will maintain its shape until tidal forces br...   » Read the article

Encyclopedia - Timeline Of The Big Bang: Encyclopedia Ii - Timeline Of The Big Bang - Planck Epoch
The Planck Epoch covers the time from 10-43 to 10-35 seconds after the Big Bang. The temperature during this epoch is estimated to decrea...   » Read the article

Encyclopedia - Trans-neptunian Object: Encyclopedia Ii - Trans-neptunian Object - Size And Composition
Most TNOs are lumps of ice with some organic (carbon-containing) material such as tholin, detected using spectroscopy. They are of the sa...   » Read the article

Encyclopedia - Extinction Event: Encyclopedia Ii - Extinction Event - Extinction Events
The classical "Big Five" mass extinctions identified by Raup and Sepkoski (1982) are widely agreed upon as some of the most significant:...   » Read the article

Encyclopedia - Definition Of Planet: Encyclopedia Ii - Definition Of Planet - Issues And Controversies
While there is much disagreement between current definitions of "planet", most focus on three general criteria: that it must orbit a star...   » Read the article

Encyclopedia - Terraforming: Encyclopedia Ii - Terraforming - Theoretical Methods Of Terraforming
Terraforming - Mars. There is some scientific debate over whether it would even be possible to terraform Mars, or how stable its climat...   » Read the article

Encyclopedia - Cretaceous-tertiary Extinction Event: Encyclopedia Ii - Cretaceous-tertiary Extinction Event - Theories
Cretaceous-Tertiary extinction event - Alvarez hypothesis. In 1980, a team of researchers led by Nobel-prize-winning physicist Luis Alv...   » Read the article

Encyclopedia - Space Probe: Encyclopedia Ii - Space Probe - List Of Space Probes
Space probe - Lunar probes. Luna program - Soviet Lunar exploration (1959-1976). Ranger program - US Lunar hard-landing probes (1961-1...   » Read the article

Encyclopedia - Cosmic Dust: Encyclopedia Ii - Cosmic Dust - Introductory Material
Cosmic Dust refers to particles in space which are assemblages of a few molecules to tenth-millimeter-sized grains. Cosmic dust can be fu...   » Read the article

Encyclopedia - Dust: Encyclopedia Ii - Dust - House Dust
The dust which collects in houses is composed of atmospheric dust combined with dust generated by the inhabitants, mostly from sloughed s...   » Read the article

Encyclopedia - Extraterrestrial Skies: Encyclopedia Ii - Extraterrestrial Skies - Mars
Mars has only a thin atmosphere; however, it is extremely dusty and there is much light that is scattered about. The sky is thus rather b...   » Read the article

Encyclopedia - Planet: Encyclopedia Ii - Planet - Definition And Classification Of Planets
Much like "continent", "planet" is a word without a precise definition, with history and culture playing as much of a role as geology and...   » Read the article

Encyclopedia - Space Colonization: Encyclopedia Ii - Space Colonization - Method
Building cities in space will require materials, energy, transportation, communications, life support, and radiation protection. Space c...   » Read the article

Encyclopedia - Fred Hoyle: Encyclopedia Ii - Fred Hoyle - Contribution To Cosmogony
An early paper of his made an interesting use of the Anthropic Principle. In trying to work out the routes of stellar nucleosynthesis, he...   » Read the article

Encyclopedia - Death Star: Encyclopedia Ii - Death Star - Description
The Galactic Empire's ultimate terror weapon, the Death Stars were battle stations (the original being 160 kilometers in diameter, Death ...   » Read the article

Encyclopedia - Charge Heraldry: Encyclopedia Ii - Charge Heraldry - Proper Charges
Heraldic writers have, somewhat arbitrarily, distinguished between "honourable ordinaries" and "sub-ordinaries". It is often said that on...   » Read the article

Encyclopedia - Deluge Prehistoric: Encyclopedia Ii - Deluge Prehistoric - The Lower Tigris-euphrates Valley Reflooding The Persian Gulf 12000 Years Ago
This is type 1. When sea levels were low, the combined Tigris-Euphrates river flowed through a wide flat marshy landscape. The Persian Gu...   » Read the article

Encyclopedia - Physicist: Encyclopedia Ii - Physicist - Astrophysicists And Physical Cosmologists
At the largest scale, astrophysicists and astronomers study the structure and motion of the universe. This branch of physics is one of th...   » Read the article

Encyclopedia - Lo!: Encyclopedia Ii - Lo! - Overview
Of Fort's four books, this volume deals most frequently and scathingly with astronomy (continuing from his previous book New Lands). The ...   » Read the article

Encyclopedia - List Of Alternative Speculative And Disputed Theories: Encyclopedia Ii - List Of Alternative Speculative And Disputed Theories - Theories
List of alternative speculative and disputed theories - Biology. See also Medicine below. Creationism is the belief that the origin ...   » Read the article

Encyclopedia - History Of The World: Encyclopedia Ii - History Of The World - Hunter-gatherers
The earliest available evidence places the origin of modern Homo sapiens in Africa about 200,000 years ago during the Palaeolithic period...   » Read the article

Encyclopedia - History Of Telescopes: Encyclopedia Ii - History Of Telescopes - Achromatic Telescope
The historical sequence of events now brings us to the discovery of the achromatic telescope. The first person who succeeded in making ac...   » Read the article

Encyclopedia - Near-earth Object: Encyclopedia Ii - Near-earth Object - Estimating The Risks
There are two schemes for classification of impact hazards: the simple Torino Scale and the more complex Palermo Technical Impact Hazard...   » Read the article

Encyclopedia - Near-earth Asteroid: Encyclopedia Ii - Near-earth Asteroid - The Nea Threat
The general acceptance of the Alvarez hypothesis, explaining the Cretaceous-Tertiary extinction event as the result of a large asteroid o...   » Read the article

Encyclopedia - Kuiper Belt: Encyclopedia Ii - Kuiper Belt - Origins
Modern computer simulations show the Kuiper belt to have been formed by the work of Jupiter, the young Jupiter having used its considerab...   » Read the article

Encyclopedia - Celestial Mechanics: Encyclopedia Ii - Celestial Mechanics - History Of Celestial Mechanics
Although modern analytic celestial mechanics starts 400 years ago with Isaac Newton, prior studies addressing the problem of planetary po...   » Read the article

Encyclopedia - Interplanetary Medium: Encyclopedia Ii - Interplanetary Medium - Composition And Physical Characteristics
The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the interplane...   » Read the article

Encyclopedia - Iapetus Moon: Encyclopedia Ii - Iapetus Moon - Physical Characteristics
The low density of Iapetus indicates that it is primarily composed of ice, with only a small amount of rocky materials. Furthermore, the ...   » Read the article

Encyclopedia - Kepler's Laws Of Planetary Motion: Encyclopedia Ii - Kepler's Laws Of Planetary Motion - Connection To Newton's Laws And Conservation Laws
Kepler did not understand why his laws were correct; it was Isaac Newton who discovered the answer to this more than fifty years later. T...   » Read the article

Encyclopedia - Kreutz Sungrazers: Encyclopedia Ii - Kreutz Sungrazers - Notable Members
The brightest members of the Kreutz Sungrazers have been spectacular objects, easily visible in the daytime sky. The three most impressiv...   » Read the article

Encyclopedia - History Of Astrology: Encyclopedia Ii - History Of Astrology - History
History of astrology - Western astrology's Babylonian origins. The history of western astrology can now be traced back to ancient Babyl...   » Read the article

Encyclopedia - Prograde And Retrograde Motion: Encyclopedia Ii - Prograde And Retrograde Motion - Retrograde Rotation
Most planets, including Earth, spin in the prograde sense: They spin in the same direction as they orbit the Sun (that is, their north ro...   » Read the article

Encyclopedia - Disaster: Encyclopedia Ii - Disaster - Natural Disasters
A Natural phenomenon can easily cause a natural disaster. Appearing to arise without direct human involvement, natural disasters are some...   » Read the article

Encyclopedia - Jan Oort: Encyclopedia Ii - Jan Oort - Honors
Awards Bruce Medal in 1942 Gold Medal of the Royal Astronomical Society in 1946 Henry Norris Russell Lectureship in 1951 Named after hi...   » Read the article

Encyclopedia - Planetary System: Encyclopedia Ii - Planetary System - Origin And Evolution Of Planetary Systems
Planetary systems around sun-like stars are generally believed to form as part of the same process which results in star formation. Some ...   » Read the article

Encyclopedia - Water Vapor: Encyclopedia Ii - Water Vapor - General Properties Of Water Vapor
Water vapor - Evaporation/sublimation. Whenever a water molecule leaves a surface, it is said to have evaporated. Each water molecule t...   » Read the article

Encyclopedia - Water Molecule: Encyclopedia Ii - Water Molecule - Physics And Chemistry Of Water
Water molecule - Density of water and ice. For most substances, the solid form of the substance is more dense than the liquid form; thu...   » Read the article

Encyclopedia - Physical Science: Encyclopedia Ii - Physical Science - Basic Principles
The foundations of the physical sciences rests upon key concepts and theories, each of which explains and/or models a particular aspect o...   » Read the article

Encyclopedia - Habitable Zone: Encyclopedia Ii - Habitable Zone - The Circumstellar Habitable Zone
The Circumstellar habitable zone (or ecosphere) is a notional spherical shell of space surrounding stars where the surface temperatures o...   » Read the article

Encyclopedia - Outer Solar System: Encyclopedia Ii - Outer Solar System - Contents And Structure
The main contents of the outer solar system are probably very numerous small bodies akin to comets from one or another population, and th...   » Read the article

Encyclopedia - Observational Astronomy: Encyclopedia Ii - Observational Astronomy - Observation Tools
The key instrument of nearly all modern observational astronomy is the telescope. This serves the dual purposes of gathering more light s...   » Read the article

Encyclopedia - Hannes Alfvén: Encyclopedia Ii - Hannes Alfvén - Research Awards And Contributions
His work was continuously disputed for many years by the senior scientist in space physics, the British-American geophysicist Sydney Chap...   » Read the article

Encyclopedia - Outer Space: Encyclopedia Ii - Outer Space - Space Does Not Equal Orbit
To perform an orbital spaceflight, a spacecraft must go higher and faster than for a sub-orbital spaceflight. A spacecraft has not made o...   » Read the article

Encyclopedia - William Herschel: Encyclopedia Ii - William Herschel - Biography
As Friedrich Wilhelm Herschel in Hanover, Germany, one of ten children (of which four died very young). In 1755 the Hanoverian Guards reg...   » Read the article

Encyclopedia - Planetarium: Encyclopedia Ii - Planetarium - Overview
The most striking feature of most planetaria is their large dome shaped projection screens onto which scenes of stars, planets and other ...   » Read the article