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64 Cards in this Set
- Front
- Back
light-year
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distance light travels in one year
1 ly= 6 trillion miles *light year is a unit of distance NOT time! |
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celestial sphere
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immense hollow sphere, imaginary object that remains a useful tool of positional astronomy
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celestial poles
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north and south, projection of earth's poles into space. Where the Earth's axis of rotation intersects the celestial sphere
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ecliptic
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imaginary circular path traced out by sun annually
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equinoxes
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where ecliptic and celestial equator intersect, exactly opposite on the celestial sphere
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vernal equinox
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sun crosses northward across celestial equator on March 21
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autumnal equinox
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sun moves southward about September 22, moment fall begins on Northern hemisphere
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summer solstice
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point on the ecliptic farthest north of the celestial equator about June 21, moment summer begins in Northern hemisphere
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winter solstice
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about December 21, sun is farthest South of the celestial equator
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zenith
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point directly overhead an observer anywhere on earth
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meridian
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great circle on the celestial sphere that passes through an observers zenith and the north and south celestial poles
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apparent solar day
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one noon to the next
their position depends on northern hemisphere versus southern hemisphere |
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right ascension
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angular distrance from the vernal equinox eastward along the celestial equator to the circle used in measuring declination. Measured in time units (hrs., min., sec.) corresponding to the time required for the sphere to rotate
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declination
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similar to latitude. The angular distance North or South of the celestial equator, measured along a circle passing through both celestial poles
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sidereal day
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time between two successive upper meridian passages of the vernal equinox
1 sidereal day= 23h56m4.091s |
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solar day
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`24 hours
-solar day is used for clocks. there is a difference between the two because astronomers use the uppser meridian to know when the optimum time to observe different objects is. |
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diurnal motion
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the daily motion of stars
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Why do we have seasons?
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We have seasons because the Earth's axis of rotation is not perpendicular to the plane of the Earth's orbit. It is tilted about 23 1/2 degrees away from the perpendicular
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what are the phases of the moon?
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new moon-> waxing crescent -> first quarter moon -> waxing gibbous moon -> full moon -> waning gibbous moon -> third quarter moon -> waning crescent moon
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eclipse
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sun, earth, and moon all lie along a straight line
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partial eclipse
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penumbra- only a portion of the sun's surface is visible
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total eclipse
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umbra- darkest part o fthe shdow, no portion of sun's surface can be seen
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annular eclipse
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a thin ring of the sun is seen around the edge of the moon
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tidal forces
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differences in the gravitational pull at different points in an object
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spring tides
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an ocean tide that occurs at new moon and full moon phases
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neap tides
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an ocean tide that occurs when the moon is near first quarter or third quarter phase
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retrograde motion
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occasional westward movement of the planets.
-the planets wander along the ecliptic |
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ptolemaic system
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each planet is assumed to move in small circles called epicycles, whose center moves around a larger circle called a deferent
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heliocentric model
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all planets, including earth, revolve around the sun
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epicycle
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small circle planet moves on. Moves eastward along deferent.
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Copernican model
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heliocentric. all planets revolve around sun at different speeds. When one overtakes another, the slower appears to be moving backwards, in retrograde motion.
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inferior planets
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Mercury and Venus
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superior planets
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Mars, Jupiter, Saturn, Uranus, Neptune
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Oceam's Razor
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the idea that simple, straightforward explanations of phenomena are most likely to be correct
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Brahe
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measured and studied stars for 20 years, basis of Kepler's studies
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Kepler's first law
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The orbit of a planet about the sun is an ellipse with the sun at one focus
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Kepler's second law
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a line joining a planet and the sun sweeps out equal areas in equal intervals of time
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perihelion
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the point in orbit when a planet is nearest the sun
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aphelion
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the point in orbit when a planet is farthest from the sun
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Kepler's third law
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p2=a3
p=planet's sidereal period, in years a=planet's semimajor axis, in AU |
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Galileo
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first to use telescope; discovered that Venus exhibits phases like the moon. He got in trouble with Roman Catholic Church for promoting a heliocentric model.
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Newton
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deduced basic laws that govern all motions on Earth as well as in the heavens
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Newton's law of inertia
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A body remains at rest, or moves in a straight line at a constant speed, unless acted upon by a net outside force
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Newton's 2nd law of motion
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F=ma
F=net outside force on an object M=mass of object a=acceleration of object |
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Newton's third law of motion
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whenever one body exerts a force on a second body, the second boddy exerts an equal and opposite force on the first body
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law of universal gravitation
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the bodies attract each other with a force directly proportional to the mass of each body and inversely proportional to the square of the distance between them
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scientific method
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basic procedure used by scientists to investigate phenomena
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Newton's form on Kepler's third law
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study of binary systems in which two stars orbit each other
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electromagnetic radiation
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radiation consisting of oscillating electric and magnetic fields
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wavelength
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the distance between two successive wave crests
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frequency
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the number of wave crests that pass a given point in one second
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energy of light
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the higher an objects temperature, the more intenself the object emits electromagnetic radiation and the shorter the wavelength at which it emits most strongly
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photon
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a discrete unit of electromagnetic energy
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refracting telescope
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a large-diameter objective lens with a longfocal length and a small eyepeiece lens of short focal length. the eye-piece lens magnifies the image formed by the objective lens in its focal plane.
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reflecting telescope
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a telescope in which the principal optical component is a concave mirror
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spectrum
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the result of dispersing a beam of electromagnetic radiation so that components with different wavelengths are sperated in space
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Kirchoff's first law
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a hot dense object (ex.-blackbody) emits a continuous spectrum covering all wavelengths
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Kirchoff's second law
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a cool transparent gas in front of a light source that itself has a continuous spectrum produces dark lines in the continuous spectrum
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blackbody
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a hypothetical perfect radiator that absorbs and re-emits all radiation falling upon it
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emission line spectra
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a series of bright spectral lines against a dark background
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absorption line spectrum
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a series of dark spectral lines among the colors of the contuous spectrum
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Doppler shift
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the apparent change in wavelength of radiation due to relative motion between the source and the observer along the line of sight
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luminosity
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the rate at which electromagnetic radiation is emitted from a star or other object. brightness and parallax
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Stefan-Boltzmann law
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A relationship between the temperature of a blackbody and the rate at which it radiates energy
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