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72 Cards in this Set
- Front
- Back
- 3rd side (hint)
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North Celestial Pole
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the point directly above North Pole
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South Celestial Pole
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the point directly above South Pole
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Celestial Equator
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projection of Earth's equator into space
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Ecliptic
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the path the Sun follows as it appears to circle around the celestial sphere once a year
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Constellation
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Region of the sky with well defined borders
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Zenith
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The point directly overhead
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Meridian
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an imaginary half-circle stretching from the horizon due south, through the zenith, to the horizon due north
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Angular Size
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angle it appears to span in your field of view
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does NOT tell the object's true size; depends on distance
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Angular Distance
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the angle that appears to separate a pair of objects
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Circumpolar stars
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Stars that never rise or set and remain perpetually above the horizon near the north celestial pole
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Do constellations change in different longitudes?
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NO, they only change with latitudes
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Summer solstice
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moment when the Northern Hemisphere receives its most direct sunlight
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Winter Solstice
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moment when the Northern Hemisphere receives its least direct sunlight
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Spring equinox
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moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the Sun
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Fall equinox
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when the Northern Hemisphere first starts to be tipped away from the Sun
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Precession
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gradually changes the orientation of Earth's axis in space
DOES NOT affect the amount of the axis tilt or the pattern of the seasons |
spinning top, as the top spins rapidly, you'll notice that its axis sweeps out a circle at a somewhat slower rate
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Apparent Retrograde Motion
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A period during which a planet appears to move westward relative to the stars
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Stellar Parallax
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shifting
depends on distance, with nearer objects exhibiting greater parallax than more distant objects |
When you hold up one finger and try to see things with your left eye and then right eye...
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Occam's razor
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The idea that scientists should prefer the simpler of two models that agree equally well with observations
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Newton's first law of motion
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An object moves at constant velocity unless a net force acts to change its speed or direction
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Newton's second law of motion
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Force= mass x acceleration
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Newton's third law of motion
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For any force, there is always an equal and opposite reaction force
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Law of conservation of momentum
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the total momentum of interacting objects cannot change as long as no external force is acting on them
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Conservation of angular momentum
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as long as there is no external torque (twisting force), the total angular momentum of a set of interacting objects cannot change
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angular momentum = mvr
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conservation of energy
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energy cannot appear out of nowhere or disappear into nothingness
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Inverse Square Law
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Doubling the distance between two objects weakens the force of gravity by a factor of 4
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Bound orbits
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orbits in which an object goes around another object over and over again
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usually ellipses
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Unbound orbits
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paths that bring an object close to another object just once
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parabolas or hyperbolas
comets |
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Center of Mass
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a point which the two objects would balance if they were somehow connected.
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If one is more massive, the center of mass would be more towards the heavier one
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Newton's version of Kepler's third law
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relationship between the orbital period and average orbital distance of a system tells us the total mass of the system
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orbital period and distance of Jupiter's moon tells us Jupiter's mass
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Orbital energy
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the sum of its kinetic and gravitational potential energies
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the planet's total orbital energy always stays the same b/c of law of conservation of energy
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Gravitational Encounter
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one way the orbits can change, exchanging orbital energy between two close objects
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Atmospheric drag
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friction can cause objects to lose orbital energy
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Escape velocity
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if an object gains enough orbital energy, it may escape its orbit
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How does gravity cause tides?
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Moon's gravity stretches Earth and its oceans
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Why do objects fall at the same time?
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Mass of object in Newton's second law exactly cancels mass in law of gravitation
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Isotopes
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same number of protons but different number of netrons
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Ionization
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stripping of electrons, changing atoms into plasma
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Dissociation
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Breaking of molecules into atoms
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What are the three basic types of spectra?
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Emission Line Spectrum
Continuous Spectrum Absorption Line Spectrum |
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Continuous Spectrum
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The spectrum of a common light bulb spans all visible wavelengths, without interruption
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Emission line spectrum
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A thin or low density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines
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Absorption Line Spectrum
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A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum
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What is the most common type of continuous spectra?
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Thermal radiation spectra
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Blueshift
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objects moving toward us
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Redshift
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objects moving away from us
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How does light tell us the rotation rate of an object?
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The width of an object’s spectral lines can tell us how fast it is rotating
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Ptolemaic model
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when Ptolemy explained apparent retrograde motion by having each planet move on a small circle whose center moves around Earth on a larger circle.
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based on Geocentric model
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Copernicus
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used a sun-centered model but he still believed that planets' orbits were perfect circles instead of ellipses
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Tycho
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his surprisingly accurate, naked eye observations provided data for Copernicus's model
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Kepler
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He found a model of planetary motion that fit Tycho's data
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What's Kepler's first law of planetary motion
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The orbit of each planet is an ellipse with the Sun at one focus
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What's Kepler's second law of planetary motion
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As a planet moves around its orbit, it sweeps out equal areas in equal times
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What's Kepler's third law of planetary motion
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More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship p^2 = a ^3
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Synchronous rotation of the Moon
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The moon rotates with exactly one orbit once
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How does your eye form an image?
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the lens bends (refracts) light rays and brings to a focus on retina
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Refraction
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the bending of light when it passes from one substance into another
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your eye uses refraction to focus light
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Focal plane
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where lights from different directions come into focus
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makes an upside down image
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How do detectors play a role in telescopes?
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they capture an image; detectors like CCD convert photons into electrons and then into an electronic image that gets stored in a computer
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What are the two most important properties of a telescope?
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Light-collecting area and Angular resolution
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Light-collecting area
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Telescopes with a larger collecting area can gather a greater amount of light in a shorter time
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A telescope's diameter tells us its light collecting area
Area= Pi (diameter/2) ^2 |
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Angular Resolution
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Telescopes that are larger are capable of taking images with greater detail
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How does light waves interference affect Angular Resolution?
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Less interference, greater resolution. Bigger telescopes have less interference
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Diffraction Limit
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The limit caused by light waves interference on angular resolution
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Refracting versus Reflecting telescopes
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Refracting focuses light with lenses while Reflecting focuses light with mirrors
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What do astronomers do with telescopes?
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Imaging (taking pictures of the sky), Spectroscopy (breaking light into spectra), Timing (measuring how light output varies with time)
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What are the best ground-based sites for astronomical observing?
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Calm (not too windy)
High (less atmosphere to see through) Dark (far from city lights) Dry (few cloudy nights) |
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How does earth's atmosphere affect observations?
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Turbulent air flow distorts our view, causing stars to twinkle and images to blur
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Adaptive optics
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rapidly changing the shape of the telescope's mirror can correct the problem of air turbulence
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Why do we put telescopes into space?
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1. Forms of light other than visible and radio do not pass thru earth's atomosphere
2. the images are much sharper |
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Name the four types of telescopes
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1. Radio telescopes
2. Infrared telescopes 3. X-ray telescopes 4. Gamma Ray telescopes |
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Interferometry
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a technique for linking two or more telescopes so that they have the angular resolution of a single large one
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