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Astronomy 6.1-10.3

Comparative planetology understanding planets by searching for and analyzing contrasts and similarities
Terrestrial planet an Earth-like planet – small, dense, rocky and metallic
Jovian planet a Jupiter-like planet with a large diameter and low density
Differentiation separation of planetary material within a planet into layers according to density
Mantle the layer of dense rock and metal oxides that lies between the molten core and Earth’s surface or a similar layer in another planet
Heavy bombardment the intense cratering that occurred sometime during the first 0.7 billion years in the history of the solar system
P wave a type of seismic wave involving compression and decompression of the material though which it passes
S wave a type of seismic wave involving lateral motion of the material through which it passes
Primary atmosphere a planet’s first atmosphere
Secondary atmosphere a planet’s atmosphere that replaces the primary atmosphere, for example by outgassing, impact of volatile-bearing planetesimals, or biological activity
Greenhouse effect the process by which an atmosphere traps hear and raises the temperature of a planetary surface
Plate tectonics one plate slides over another, causing volcanism
Rift valley forms where continental plates begin to pull apart
Mid-ocean rises formed when plates spread apart and magma rises
Basalt a rock typical of solidified lava
Subduction zone a deep trench where one plate slides under another
Global warming the gradual increase in the surface temperature of Earth caused by human modifications to Earth’s atmosphere
Folded mountain range can form where plates push against each other
Mare one of the lunar lowlands filled by successive flows of dark lave, from the Latin for “sea.” Plural: “maria.”
Albedo the ratio of the amount of light reflected from an object to the amount of light received by the object. Equals 0 for perfectly black and 1 for perfectly white
Ejecta pulverized rock scattered by meteorite impacts on a planetary surface
Anorthosite Aluminium-and calcium-rich silicate rock found in the lunar highlands
Breccia rock composed of fragments of older rocks bonded together
Large-impact hypothesis hypothesis that the moon formed from debris ejected during a collision between Earth and a large object
Magma ocean the exterior of the newborn moon, a shell of molten rock hundreds of kilometers deep
Multiringed basin large impact feature (crater) containing two or more concentric rims formed by fracturing of the planetary crust
Late heavy bombardment the sudden temporary increase in the cratering rate in our solar system that occurred about 4 billion years ago
Micrometeorite meteorite of microscopic size
Coronae on Venus, large round geological faults in the crust caused by the intrusion of magma below the crust
Runaway greenhouse effect a greenhouse effect so dramatic that it amplifies itself, becoming stronger with time
Permafrost permanently frozen soil
Shield volcano wide, low-profile volcanic cone produced by highly liquid lava
Outflow channel geological features on Mars and Earth caused by flows of vast amounts of water released suddenly
Valley network a system of dry drainage channels on Mars that resembles the beds of rivers and tributary streams on Earth
Oblateness the flattening of a spherical body , usually caused by rotation
Liquid metallic hydrogen a form of liquid hydrogen that is a good electrical conductor, inferred to exist in the interiors of Jupiter and Saturn
Magnetosphere the volume of space around a planet within which the motion of charged particles is dominated by the planetary magnetic field rather than the solar wind
Belt-zone circulation the atmospheric circulation typical of Jovian planets in which dark belts and bright zones encircle the planet parallel to its equator
Forward scattering the optical property of finely divided particles to preferentially direct light in the original direction of the light’s travel
Roche limit the minimum distance between a planet and a satellite that can hold itself together by its own gravity
Tidal heating the heating of a planet or satellite because of friction caused by stretching due to the gravitational influence of a nearby body
Shepherd satellites gravitationally usher straying particles back into the rings
dwarf planet a body that orbits the sun, is not a satellite of a planet, is massive enough to pull itself into a spherical shape but not massive enough to clear out other bodies in and near its orbit. for example, pluto, eris ,and ceres
asteroid small, rocky world. most orbit mars and jupiter in a belt
comet one of the small, icy bodies that orbit the sun an produce tails of gas and dust when they approach the sun
terrestrial planets small, dense, rocky worlds with little or no atmosphere (inner four planets)
jovian planets large, low-density worlds with thick atmospheres and liquid or ice interiors (outer four planets)
volatile easily vaporized
kuiper belt the collection of icy objects orbiting in a region from just beyond neptune out to 50 AU or more
meteor a small bit of matter heated by friction to incandescent vapor as it falls into Earth's atmosphere
meteoroid a meteor in space before it enters earths atmosphere
meteorite a meteor that survives its passage through the atmosphere and strikes the ground
carbonaceous chondrite stony meteorite that contains small glassy spheres called chondrules and volatiles. these chondrites may be the least-altered remains of the solar nebula still present in the solar system
widmanstatten pattern bands in iron meteorite sections due to large metal crystals
meteor shower a display of meteors that appear to come from one point in the sky, understood to be cometary debris
half-life the time required for half of the radioactive atoms in a sample to decay
solar nebula theory the theory that the planets formed from a spinning disk of material around the forming sun
uncompressed density the density a planet would have if its gravity did not compress it
ice line boundary beyond which vapor could freeze to form ice
condensation sequence the sequence in which different materials condense from the osolar nebula depending on distance from the sun
planetesimal one of the small bodies that formed from the solar nebula and eventually grew into protoplanets. asteroids and comets are remnants of the planetesimals
condensation the growth of a particle by addition of material from surrounding gas, atom by atom
accretion the sticking together of solid particle to produce a larger particle
protoplanet massive object, destined to become a planet, resulting from the coalescence of planetesimals in the solar nebula
gravitational collapse the process by which a forming body such as a planet gravitationally captures gas rapidly from the surrounding nebula
differentiation the separation of planetary material inside a planet according to density
outgassing the release of gases from a planet's interior
NEO (near earth object) a small solar system body (asteroid or comet) with an orbit near enough to earth that it poses some threat of eventual collision
evolutionary theory an explanation of a phenomenon involving slow, steady processes of the sort seen happening in the present day
catastrophic theory an explanation of a phenomenon involving special, sudden, perhaps violent, events
heat of formation in planetology, the heat released by infalling matter during the formation of the planetary body
oort cloud the hypothetical source of comets, a swarm of icy bodies understood to lie in a spherical shell extending to 100,000 AU from the sun
stellar parllax (p) the small apparent shift in position of a nearby star relative to distant background objects due to earths orbital motion
parsec (pc) the distance to a hypothetical star whose parallax is 1 arc second
intrinsic brightness a measure of the amount of light a star produces
absolute visual magnitude intrinsic brightness of a star. the apparent visual magnitude the star would have if it were 10 pc away
luminosity (L) the total amount of energy a star radiates per second at all wavelengths
spectral class a star's label in the temperature classification system based on the appearance of the stars spectrum
spectral sequence the arrangement of spectral classes (O, B, A, F, G, K, M) ranging from hot to cool
brown dwarf a very cool, low-luminosity star whose mass is not sufficient to ignite nuclear fusion
L dwarf, T dwarf spectral classes of brown dwarf stars with lower surface temperatures and luminosities than M dwarfs
Y dwarf a substellar object with temperature below 500 K, having inferred properties intermediate between brown dwarfs and Jovian planets
hertzsprung-russell (H-R) diagram a plot of the intrinsic brightness versus the surface temperature of stars. it separates the effects of temperature and surface area on stellar luminosity
main sequence the region of the H-R diagram running from upper left to lower right, which includes roughly 90 percent of all stars generating energy by nuclear fusion
giant large, cool, highly luminous star in the upper right of the HR diagram, typically 10 to 100 times the diameter of the sun
supergiant exceptionally luminous star whose diameter is 100 to 1000 times that of the sun
red dwarf a faint, cool, low-mass, main-sequence star
white dwarf dying star at the lower left of the HR diagram that has collapsed to the size of Earth and is slowly cooling off
luminosity class a category of stars of similar luminosity, determined by the widths of lines in their spectra
spectroscopic parallax the method of determining a stars distance by comparing its apparent magnitude with its absolute magnitude as estimated from its spectrum
binary star pairs of stars that orbit around their common center of mass
visual binary system a binary system in which the two stars are separately visible in the telescope
spectroscopic binary system a star system in which the stars are too close together to be visible separately. we see a single point of light, and only by taking a spectrum can we determine that there are two stars
eclipsing binary system a binary star system in which the stars cross in front of each other as seen from earth
light curve a graph of brightness versus time commonly used in analyzing variable stars and eclipsing binaries
nuclear forces the two forces of nature that only affect the particles in the nuclei of atoms
nuclear fission reactions that break the nuclei of atoms into fragments
nuclear fusion reactions that join the nuclei of atoms to form more massive nuclei
coulomb barrier the electrostatic force of repulsion between bodies of like charge, commonly applied to atomic particles
proton-proton chain a series of three nuclear reactions that builds a helium atom by adding together protons. the main energy source in the sun
deuterium an isotope of hydrogen in which the nucleus contains a proton and a neutron
neutrino a neutral, nearly massless atomic particle that travels at or nearly at the speed of light
CNO (carbon-nitrogen-oxygen) cycle a series of nuclear reactions that use carbon as a catalyst to combine four hydrogen nuclei to make one helium nucleus plus energy, effective in stars more massive than the sun
brown dwarf a stellar object with such low mass that it cannot raise its central temperature high enough to sustain hydrogen fusion
zero-age main sequence (ZAMS) the location in the HR diagram where stars first reach stability as hydrogen-burning stars
Created by: pace_sauce