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64 Cards in this Set

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light-year
distance light travels in one year
1 ly= 6 trillion miles

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