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60 Cards in this Set

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Astronomy
The study of the objects that lie beyond our planet Earth, and of the processes by which these objects interact with one another
Historical Science
What we observe has already happened in the universe and we can do nothing to change it
Light Year
The distance that light travels in one year
Planet
A body of significant size that orbits a star and does not produce its own light
Brown Dwarfs
A class of objects intermediate between stars and planets; are failed stars- balls of hot gas that do not have what it takes to keep producing significant amounts of light
Galaxy
Group of stars
Dark Matter
Nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; composition is not known
Universe
Everything that exists that is accessible to our observations
Quasars
Brilliant centers of galaxies, glowing with the light of some extraordinarily energetic process
Geocentric
Earth-centered
Zenith
The top of the dome that is directly above your head
Horizon
The line where the dome meets the Earth
Celestial Sphere
Apparent sphere of the sky; a sphere of large radius centered on the observer. Directions of objects in the sky can be denoted by their position on the celestial sphere
Axis
The imaginary stick that our planet rotates on
North Celestial Pole & South Celestial Pole
The points where the axis meets the celestial sphere
Celestial Equator
A great circle on the celestial sphere 90 degrees form the celestial poles; where the celestial sphere intersects the plane of the Earth's equator
North Circumpolar Zone
The area within 38 degrees of the North pole
South Circumpolar Zone
The area within 38 degrees of the South Pole
Ecliptic
The path the Sun appears to take around the celestial sphere each year
Constellation
One of 88 sectors into which astronomers divide the celestial sphere; many constellations are named after a prominent group of stars within them that represents a person, animal, or legendary creature form ancient mythology
Zodiac
A belt around the sky about 18 degrees wide centered on the ecliptic
Cosmology
Our concept of the cosmos (its basic structure and origin)
Parallax
The apparent shift in the direction of an object as a result of the motion of the observer
Stellar Parallax
The shift in the apparent direction of a star due to the Earth's orbital motion
Magnitude
A system for measuring the amount of light flux received from a star or other luminous object; the higher the magnitude, the less radiation we receive from the object
Retrograde Motion
An apparent westward motion of a planet on the celestial sphere or with respect to the stars
Epicycle
A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle
Ellipse
A flattened circle
Focus
One of two fixed points inside an ellipse from which the sum of the distances to any point on the ellipse is a constant
Major Axis
The widest diameter of an ellipse
Semimajor Axis
Half the distance of the major axis; usually used to specify the size of the ellipse
Eccentricity
The ratio of the distance between the foci to the length of the major axis
Kepler's First Law
Each planet moves about hte Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse
Kepler's Second Law
The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
Kepler's Third Law
The squares of the planets' periods of revolution are in direct proportion to the cubes of the semimajor axes of their orbits
Newton's First Law
Every body continues doing what it is already doing- being in a state of rest or moving uniformly in a straight line- unless it is compelled to change by an outside force
Newton's Second Law
The change of motion of a body is proportional to the force actin on it and is made in the direction in which that force is acting
Newton's Third Law
To every action there is an equal and opposite reaction (or the mutual actions of two bodies upon each other are always equal and act in opposite directions)
Conservation of Angular Momentum
The law that the total amount of angular momentum in a system remains the same (in the absence of any force not directed toward or away from the point or axis about which the angular momentum is conserved
Angular Momentum
A measure of the momentum of an object as it rotates or revolves about some fixed point
Gravity
The mutual attraction of material bodies or particles
Orbit
The path of an object through space
Perihelion
The place in the orbit of an object revolving about the Sun where it is closest to the Sun's center
Aphelion
Point in its orbit where an Earth satellite is farthest from the Earth
Perigee
The place in the orbit of an Earth satellite where it is closest to the center of the Earth
Apogee
Point in its orbit where an Earth satellite is farthest from the Earth
Asteroid Belt
The great majority of asteroids in our solar system that lie between 2.2 and 3.3 AU
Circular Satellite Velocity
The critical speed that a revolving body must have in order to follow a circular orbit
Escape Velocity
The velocity a body must achieve to break away from the gravity of another body and never return to it
Great Circle
Any circle on the surface of sphere whose center is at the center of the sphere
Declination
Angular distance north or south of the celestial equator
Right Ascension
A coordinate for measuring the east-west positions of celestial bodies; the angle measured eastward along the celestial equator from the vernal equinox to the hour circle passing through a body
Solar Day
The rotation period of the Earth with respect to the Sun
Sidereal Day
Period of the revolution of one body about another measured with respect to the stars
Apparent Solar Time
Time as measured by the position of the Sun in the sky (the time that would be indicated by a sundial)
Mean Solar Time
Based on the average value of the solar day over the course of the year; contains exactly 24 hours
Phases
A particular point in the time of a cycle or any distinct time period in a sequence of events
Eclipse
Occurs whenever any part of either the Earth or the Moon enters the shadow of the other
Solar Eclipse
When the sun is at least partially covered by the Moon
Lunar Eclipse
When the Moon passes into the shadow of the Earth