ASTR 101: FINAL EXAM
43 Cards in this Set
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terrestrial planet
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small, high-density planet with solid, rocky surface (silicate mantle surrounding Fe-Ni core): Mercury, Venus, Earth, Mars
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jovian planet
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gas giant (thick atmospheres primarily composed of H and He, low densities, large diameters): Jupiter, Saturn, Uranus, Neptune
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differentiation
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geological process by which magma separates into layers of igneous rock of differing density and composition within body; on planetary scale, produces core, mantle, and crust
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Widmanstätten pattern
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cross-hatched pattern on Fe/Ni meteorites, resulting from intergrowth of minerals kamacite and taenite as meteorite parent body slowly cooled in space
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carbonaceous chondrite
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most primitive chondrite meteorite with compositions that most nearly resemble Sun (high [carbon] and [organics]), originating from parent bodies' collision
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trans-Neptunion object
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small, icy body orbiting Sun beyond Neptune (includes Pluto in Kuiper Belt); scattered-disk objects are in 3:2 orbital resonance and are known as Plutinos
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Oort cloud
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since new comets approach Sun on highly elliptical orbits at all inclinations, proposal of roughly spherical halo of comet nuclei from formation of solar system out to ~ 100 000 AU
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comet
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small body, composed of ice and dust, in highly eccentric orbit around Sun (not confined to ecliptic)
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refractory
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element or compound that melts/vaporizes or condenses from gas at high temperature: Al, Ca, U; volatile antonym
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planetesimal
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body of rock and/or ice presumed to have formed in early history of solar system (accumulation = planet formation); most left over from planetary accretion ejected by perturbations of planets into Kuiper Belt and Oort Cloud
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accretion
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mass of body increases by accumulation of matter (gas or small solid bodies which collide with and adhere), by which bodies in solar system thought to have grown
"core" = planet of 10 solar masses (jovian) can accrete gas directly from nebula
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obliquity (of ecliptic)
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"Earth's axial tilt" = angle between Earth's equator and ecliptic
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photodissociation
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if cool molecular gas cloud is diffuse, all molecules may be dissociated by starlight; photodissociation regions are thereby formed at edges and boundaries
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gravitational lens
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light rays bent by gravitational field of massive object (galaxy or black hole), seen as formation of double or multiple images of distant galaxy or quasar by a foreground object, or Einstein rings
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albedo
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reflective property of non-luminous body: 0.0 (blackhole, absorbs all incident light) to 1.0 (mirror); planets or planetary satellites with dense atmospheres > those with transparent or no atmospheres
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reflection spectroscopy
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measures starlight reflected by planet (molecules in atmosphere produce absorption bands due to transitions between different vibrational energy levels)
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Transmission spectroscopy
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measures star during planetary transit (if planet has atmosphere, some light passes through it and will be absorbed at specific wavelengths)
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hot Jupiter
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planet with mass similar to Jupiter but lying close to its parent star (tidally locked), with nearly-circular orbital period from few days to weeks (believed to have formed farther from parent stars and subsequently moved inwards); first extrasolar planets discovered
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habitable zonE
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orbital region around star where planet might be able to retain liquid water on its surface and possibly support life
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Gravitational scattering
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deflection of object path passing near massive body = large, sudden change in orbital parameters (Jupiter can capture comets in an elliptical orbit or throw them out of solar system)
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resonance
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period gravitational effect of one object on another = bodies' mutual perturbations repeat at nearly same points in their orbits (building up to produce large oscillations/driving one of bodies into another orbit)
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planetary migration
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planet towards or away from its parent star as a result of aerodynamic drag from gas, random gravitational interactions with planetesimals, or resonant interactions with other coorbiting bodies (hot Jupiters)
Type I = planet orbits within debris disk, creating density waves (gravitati…
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interstellar absorption
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absorption of starlight by dust and gas in space between stars; increases towards shorter-wavelength (blue) end of spectrum, hence makes stars appear redder = "interstellar reddening"
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halo
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material in roughly spherical distribution around galaxy: population of old stars (Pop II), including globular clusters, with little to no rotation about galactic centre; highly ionized high-temperature gas; extended distribution of invisible dark matter
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bulge
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roughly spherical distribution of stars that forms the central hub of spiral galaxies (older and lower metallicity)
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elliptical galaxy
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Pop II stars, lacking blue stars (no formation for ~ 2 by), and little or no interstellar gas or dust (jets)
dE, D, cD = dwarf, giant, supergiant ellipticals (massive examples found at cluster centres)
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effective radius
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"half-light radius" = half of galaxy's luminosity is contained
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starburst galaxy
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energy output dominated by radiation from recently formed stars; radiation is emitted mainly in UV region from hot, young massive stars, but is absorbed and re-emitted by dust in interstellar space to give very high luminosities at far infrared wavelengths
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dwarf spheroidal galaxy
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most common type of galaxy in Universe: blue stars ✓, contain little or no interstellar material, not so centrally concentrated (as E. galaxy), have low density, low surface brightness, and a decrease of light output with radius, implying that they are more closely related to small disk g…
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spiral galaxy
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bright arms of stars, gas, and dust that extend in a spiral pattern from central hub (spheroidal bulge of Pop II stars) in disk galaxies; spiral arms sites of active star formation, appearance dominated by bright, blue, massive young stars of Pop I and gaseous H II regions
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Population I
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stars (Sun) that lie in disk of galaxy and have high [heavy elements]; probably formed continuously during lifetime of disk from gas enriched by debris from supernovae in Pop II stars
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Population II
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stars found in halo and central bulge of galaxy, with low [heavy elements]; formed in first billion years or so of galaxy's life, before formation of galactic disk
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tidal tail
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consisting of stars pulled away from parent galaxy by gravitational tidal force of another galaxy during close encounter
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irregular cluster
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loose, clumpy distribution of galaxies with high gas content (undergoing star formation); high fraction of spiral galaxies
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morphology-density relation
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clusters having high density have a larger fraction of elliptical and S0 galaxies; within given cluster, early-type galaxies are found primarily in denser regions of cluster
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mass-to-light ratio
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ratio of total mass to total luminosity expressed in solar units (Sun = 1); (L ~ M^3.5)
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dynamical friction
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Force experienced by mass (star cluster/dwarf galaxy) travelling through extended distribution of stars; gravitational effect of mass as it moves causes slight enhancement of density of stars behind it, and consequent increased gravitational influence acts as drag on mass (merging of gala…
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Seyfert galaxy
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galaxy much like spiral with small, bright nucleus which shows broad, strong emission lines in its spectrum; lower-luminosity examples of quasar activity
Type 1 have broad emission lines of hydrogen but narrow forbidden lines of heavier elements; Type 2 have both broad lines
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quasar
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object with high redshift which looks like a star, but is actually very luminous active nucleus of distant galaxy; redshifted spectra show strong, often very broad, emission lines as well as continuum radiation
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blazar
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high-speed jet of plasma and radiation (X/gamma) from an active galactic nucleus viewed nearly end-on; broad emission lines in their spectra: low-frequency peak corresponds to synchrotron emission; high-frequency peak results when high-energy electrons collide with photons of cosmic micr…
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M-sigma relation
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mass of central black hole correlates with mass of galactic bulge, as measured by velocity dispersion of stars in bulge: M.BH ∝ σ^5
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Faber-Jackson relation
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M.BULGE ∝ σ^4; M.BH ∝ M.BULGE^(5/4)
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aberration
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small apparent difference between observed direction of star and its true direction, due to combined effect of observer's motion across path of incoming starlight and finite velocity of light.
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Study Guide ASTR 101