ASTR 120 Midterm 2

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nikachan
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305632
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ASTR 120 Midterm 2
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2015-07-24 01:00:50
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astronomy definitions vocab
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Definitions of astronomy terms
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  1. Angular distance
    The distance between two "lines" drawn from the eye to connect two close stars
  2. Angular diameter
    measurement to describe the apparent size of a celestial object. (also called angular size)
  3. Astronomical unit (AU)
    average distance between earth and the sun (also semi-major axis of earth's orbit around the sun)
  4. Light-year (ly)
    the distance light travels in one year
  5. Parsec (pc)
    the distance at which 1 AU subtends an angle of 1 arcsec
  6. geocentric model
    model of universe where the earth is stationary while the sun, moon, stars and planets revolve around it
  7. direct motion
    the eastward motion of planets relative to the stars
  8. retrograde motion
    the westward motion of planets relative to the stars
  9. Ptolemaic system
    most enduring model to explain retrograde motion within the geocentric model using epicycles and deferents
  10. epicycle
    small circle each planet was assumed to move around, centered on the deferent
  11. deferent
    larger circle planet's epicycle moved around, centered on the earth
  12. heliocentric model
    model of solar system in which all planets, including earth, orbit the Sun
  13. ecliptic
    the projection onto the celestial sphere of the plane of earth's orbit
  14. period
    time it takes a planet to complete one orbit
  15. synodic period
    time that elapses between two successive identical configurations as seen from earth (time it takes for a planet to appear in the same spot of the sky compared to the stars)
  16. sidereal period
    time it takes a planet to complete one full orbit of the sun relative to the stars
  17. parallax
    the apparent change in position of an object due to the observers movement
  18. Nicolaus Copernicus
    devised the first comprehensive heliocentric model
  19. Tycho Brahe's
    astronomical observations disproved ancient ideas about the heavens
  20. Johannes Kelper
    proposed elliptical paths for the planets movement around the Sun
  21. major axis

    semi-major axis
    longest diameter of an ellipse

    half the distance of the major axis (also mean distance between planet and star)
  22. eccentricity
    describes the shape of an ellipse which depends on its elongation
  23. perihelion
    point on orbit closest to the Sun causing the planet to move most rapidly
  24. aphelion
    point on orbit farthest from Sun causing planet to move most slowly
  25. Kepler's first law
    the orbit of a planet about the Sun is an ellispe with the sun at one focus
  26. Kepler's second law
    a line joining a planet and the sun sweeps out equal areas in equal intervals of time (lso called law of equal areas)
  27. Kepler's third law
    the square of the sidereal period of a planet is directly proportional to the cube of the semi-major axis of the orbit
  28. Galileo
    discoveries with a telescope strongly supported a heliocentric model
  29. Newton
    formulated laws of motion and gravity that describe fundamental properties of physical reality
  30. Newton's first law of motion
    an object remains at rest, or moves in a straight line at a constant speed, unless acted on by a net outside force
  31. Newton's second law of motion
    in order to give an object acceleration a net outside force must act upon it
  32. weight
    the force of gravity that acts on an object
  33. Newton's third law
    whenever one object exerts a force on a second object, the second object exerts an oppositely dircted force of equal strength on the first
  34. law of universal gravitation
    two objects attract each other with a force that is directly proportional to the mass of each object and inversely proportional to the square of the distance between them
  35. orbital energy
    trajectories with both kinetic and gravitational potential energy
  36. escape speed
    energy required to break out of bound orbits and never return to the original source of gravity
  37. tidal forces
    difference in gravitational pull at different points in an object
  38. blackbody
    ideal type of dense object, reflects no light but instead absorbs all radiation falling on it
  39. blackbody radiation
    light emitted by a blackbody as a result of temperature
  40. energy flux
    "rate of flow"; the amount of energy emitted from each square meter of an object's sureface in a second
  41. Wien's law
    relates temperature to wavelength of maximum emission
  42. Stefan-Boltzmann law
    relates flux to temperature
  43. photon
    particle of light, a distinct packet of electromagnetic energy
  44. spectral lines
    fine dark lines in solar spectrum caused when light at a specific wavelength is partially absorbed (also called absorption lines)
  45. Kirehhoff's law: 1
    a hot, opaque body, such as a perfect blackbody or a hot dense gas produces a continuous spectrum (a complete rainbow of colors without any spectral lines)
  46. Kirehhoff's law:2
    a hot, transparent gas produces an emission line spectrum
  47. emission line spectrum
    a series of bright spectral lines against a dark background
  48. Kirehhoff's law: 3
    a cool, transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum
  49. absorption line spectrum
    a series of dark spectral lines amoung the solors of the continuous spectrum
  50. Balmer lines
    the spectral lines of hydrogen at visible wavelengths
  51. Lyman series
    series of spectral lines completely in the ultraviolet, n=1
  52. Paschen series
    series of spectral lines completely in the infrared, n=3
  53. blueshift
    as light source moves closer to observer, all lines in spectrum are shifted toward the short-wavelength end of the spectrum
  54. red shift
    as light source moves away from observer, all lines in spectrum are shifted toward the long-wavelength end of the sepctrum
  55. Doppler effect
    the effect of relative motion on wavelength
  56. light gathering power
    the ability of a telescope to detect light. directly proportional to area of object lens which in turn is proportional to the square of the lens' diameter
  57. chromatic aberration
    optical defect caused by light bending differently in different lenses and resulting in fuzzy, rainbow colored halos
  58. refracting telescope
    telescope using two lenses to make an image formed on a focal plane appear larger
  59. refecting telescope
    telescope that uses a curved mirror to make an image of a distant object
  60. angular resolution
    quantity that gauges how well fine details can be seen
  61. diffraction
    tendency of light waves to spread out when they are confined to a small area like the lens or mirror of a telescope
  62. seeing disk
    a measure of the limit that atmospheric turbulence places on telescope's resolution
  63. very long baseline interferometry
    technique to obtain better angular resolution by combining the signal of radio telescopes at different observatories 1000s of km apart
  64. luminosity
    total amount of energy emitted by a star
  65. hydrogen fusion
    process of converting hydrogen into helum through a nuclear reaction
  66. proton-proton chain
    process of converting 4 hydrogen nuclei into one helium nucleus
  67. hydrostatic equilibrium
    the outer layers of stellar mater are held in place (neither exploding or collapsing nor significantly heating or cooling) because downward pressure of pressure of layers of material and weight of material are balanced by the upward pressure of hot gases beneath them
  68. thermal equilibrium
    while temperature in solar interior is different at different depthes the temperature at each depth remains constant in time
  69. neutrinos
    particles that have no electric charge
  70. photosphere
    single thin layer of gas that all of the sun's visible light emanates from creating what appears to be a sharp, well defined solar surface
  71. chromosphere
    glowing pinking layer of gas above the photosphere revealed during total solar eclipse
  72. corona
    outermost layer of sun's atmosphere
  73. solar wind
    coronal gas that escapes sun's atmosphere due to corona's high temperature
  74. sunspots
    irregularly shaped dark regions in the photosphere caused by differential roation making the sun's poles not aligned all the time
  75. sunspot cycle
    phenomenon where average number of sunspots is not constant but varies in a predictable pattern (11 years between two sunspot maximims or two sunspot minimums)
  76. 22-year solar cycle
    the time ti takes the Sun's magnetic pattern to repeat itself (occurs after 2 sunspot cycles
  77. space weather
    variations in the solar wind and magnetic field that can affect satellites and astronauts
  78. magnetic reconnection
    process in which, if two magnetic fields of two arches come into proximity, their magnetic field can rearrange
  79. space velocity
    describes how fast and in what direction a star is moving
  80. tangential velocity
    star's velocity perpendicular to our line of sight
  81. proper motion
    the number of arcsecs that the star appears to move per year on selestial plane
  82. radial velocity
    star's motion parallel to our line of sight
  83. brightness
    the amount of energy that passes each second through a square meter of the sphere's surface area
  84. apparent magnitude
    describe how bright an object appears to an earth-based observer
  85. absolute magnitude
    measure a star's true energy output by calculating the star's apparent magnitude if it were located 10 pc from earth
  86. spectra classes
    groups of similar appearing stellar spectra (Oh, Be A Fine Girl Kiss Me)
  87. Hertsprung-Russell diagrams
    graphs showing relationship/trneds between stars absolute magnitude (luminosity) and surface temperature
  88. interstellar medium
    combination of gas and dust that spans the space between stars
  89. dark nebula
    nebula so opaque it blocks any visible light coming from stars that lie behind it
  90. interstellar reddning
    effect where light from remote stars is reddened as it passes through the interstellar medium because the blue component of their starlight is scattered and absorbed by interstellar dust
  91. Dok globules
    other relatively small, nearly spherical dark nebulae
  92. protostars
    clumps formed within densest portions of dark nebulae that contract under their own mutual gravitational attractoin
  93. clusters
    groups of young stars

    open: a loose collection of stars

    stellar association: group of stars gravitationally unbound from the beginning
  94. giant molecular clouds
    huge clouds that contain enormous amounts of hydrogen
  95. supernova remnants
    nebulae that are the shredded funeral shrouds of dead stars
  96. core hydrogen fusion
    process of converting hydrogen to helium through thermonuclear fusion that takes place in the core of main sequence stars
  97. min sequence lifetime
    total time a star spends fusing hydrogen into helium at its core
  98. red dwarfs
    stars of spectral class M having masses between 0.08 and 0.4 solar mass
  99. shell hydrogen fusion
    in stars with more than 0.4 solar mass, hydrogen fusion continues in materiel just outside the core after all hydrogen in the core has been consumed
  100. red giants
    as shell hydrogen fusion works it way outward, luminosity increases and radius increases causing outer layers to cool and surface temperature to drop.
  101. core helium fusion
    helium fusion that takes place in a red giants core after it reaches temperatures of 108 K
  102. triple alpha process
    process of fusing 3 helium nuclei to form a carbon nucleus
  103. helium flash
    in red giants with a mass less that about 2-3 solar mass, helium fusion beings explosively and suddenly
  104. degenercy
    phenomenon in which closely packed particles resist compression as a consequence of the Pauli exclusion principle
  105. Pauli exclusion principle
    states that two electrons cannot simultaneously occupy the same quantum state
  106. turn off point
    peak of the surviving portion of the main sequence stars on the cluster's H-R diagram
  107. Population 1 stars
    (metal rich) stars whose spectra contain many prominent spectral lines of heavy elements
  108. Population 2 stars
    (metal poor) stars whose spectra show weak lines of heavy elements
  109. pulsating variable stars
    stars that undergo substantial changes in size, their surface temperature varies and vary dramatically in brightness
  110. Cepheid variable
    characterized by rapid brightening followed by gradual dimming
  111. red giant branch
    as luminosity increases and surface temperature drops, post main sequence stars move up and to the right of H-R digram
  112. core helium fusion
    second post main sequence stage
  113. horizontal branch
    stars with helium fusing cores and hydrogen fusion shells
  114. shell helium fusion
    after all helium in red giant core has been burned the core contracts releasing heat and beginning helium fusion in thin shell around the core (second phase of red giants)
  115. asymptotic giant branch stars
    stars in second red giant phase
  116. planetary nebula
    low mass stars eventually become a fiercely hot, exposed core, surrounded by glowing shells of ejected gas
  117. white dwarf
    relic of star created when there's no nuclear reactions occuring so core cools down like dying ember
  118. Chandrasekhar limit
    upper limit to mass of a white dwarf
  119. superjiant
    star whose luminosity and radius are much larger than those of a giant caused by nuclear reactions simultaneously in several shells
  120. supernova
    when shock wave breaks out of the star, a portion of the explosive energy escapse in a torrent of light
  121. core-collapse supernova
    type of supernova that occurs when there is no more fuel to burn in core so the star falls in on it's self due to gravitational forces but bounces back because of degenerate neutron pressure, sending a shock wave through layers of the star resulting in supernova
  122. progenitor star
    star before it "goes supernova"
  123. Cherenkov radiation
    shock wave caused by positron that moves through a substance faster than the speed of light in that substance
  124. Type 2 supernovae
    supernovae with hydrogen emission lines (core-collapse supernova)
  125. Type 1a supernovae
    have spectra that include strong absorption line of ionized silicon but not hydrogen lines
  126. Type 1b Supernovae
    lack ionized silicon line as well as lack hydrogen line but have strong helium absorption line
  127. Type 1c Supernovae
    lack ionized silicon line, helium absorption line and hydrogen line
  128. Thermonuclear supernova
    Type 1a supernova caused by the thermonuclear explosion of a white dwarf
  129. neutron star
    an incredibly dense sphere composed of mostly of neutrons
  130. pulsars
    pulsating radio sources, neutron stars rapidly rotating

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