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Discovering the Essential Universe Chapter 2
Flashcard set for chapter 2 of 'discovering the essential universe' for college level Astronomy 101 class.
64
Science
Undergraduate 2
09/17/2014

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Term
Science
Definition
Both a body of knowledge and a process of learning about nature.
Term
Scientific Method
Definition
A process by which scientists (ideally) go about observing, explaining and predicting physical reality.
Term
Occam's Razor
Definition
When several competing theories describe the same concepts with the same accuracy, choose the simplest one.
Term
geocentric cosmology
Definition
The belief that everything revolves around the Earth.
Term
heliocentric cosmology
Definition
The belief that everything revolves around the sun.
Term
cosmology
Definition
A theory of the overall structure and evolution of the universe.
Term
direct motion
Definition
Slow movement of the planets eastward (leftward) compared to the stars.
Term
retrograde motion
Definition
Slow movement of the planets to the right (west) compared to the stars.
Term
conceptual framework
Definition
contains all the information we take for granted.
Term
Ariastarchus
Definition
First to propose heliocentric cosmology.
Term
Copernicus
Definition
Devised the first comprehensive heliocentric cosmology.
Term
configurations
Definition
Geometric relationships between Earth, any other planet, and the sun.
Term
inferior conjunction
Definition
A planet is directly between Earth and the Sun.
Term
superior conjunction
Definition
Sun is directly between Earth and Mercury or Venus.
Term
elongation
Definition
Angle between the Sun and a planet as viewed from Earth.
Term
greatest eastern/western elongation
Definition
Mercury and Venus are as far from the Sun in angle as they can be.
Term
conjunction
Definition
When a planet appears to be behind the Sun as seen from Earth.
Term
opposition
Definition
When a planet is opposite the Sun in the sky.
Term
sidereal period
Definition
Time it takes a planet to make on orbit of the Sun.
Term
synodic period
Definition
Time that elapses between two successive identical configurations as seen from Earth.
Term
Tycho Brahe
Definition
Used parallax to prove the 1572 supernova explosion was much further away than previously believed.
Term
Parallax
Definition
Variation in angle from viewing an object from different locations.
Term
focus (foci)
Definition
Two points inside an ellipse through which it's longest diameter passes.
Term
major axis
Definition
passes through both foci across ellipse.
Term
semimajor axis
Definition
Half the length of the major axis. Also the average distance between a planet and the sun.
Term
Kepler's First Law
Definition
The orbit of a planet around the sun is an ellipse with the Sun at one focus.
Term
orbital eccentricity
Definition
Measure of the shape of a planet's orbit around the sun, ranging for circular to nearly a straight line.
Term
perihelion
Definition
The part of a planet's orbit nearest the Sun.
Term
aphelion
Definition
The part of a planet's orbit furthest from the Sun.
Term
Kepler's Second Law
Definition
A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.
Term
Kepler's Third Law
Definition
The square of a planet's sidereal period around the Sun is directly proportional to the cube of the length of it's orbit's semimajor axis.
Term
mass
Definition
Measure of the total number of particles contained in a unit (expressed in kg).
Term
weight
Definition
Force with which you push down on a scale due to gravitational attraction of the world on which you stand.
Term
Galilean Moons
Definition
Io, Europa, Ganymede, Callisto.
Term
gravity
Definition
attraction between all objects due to their masses.
Term
Newton's First Law
Definition
Law of Inertia: Inertia is the property of matter that keeps an object at rest or moving in a straight line at a constant speed unless acted upon by a net external force.
Term
friction
Definition
Helps slow things down.
Term
velocity
Definition
Speed and direction of motion.
Term
acceleration
Definition
The rate at which velocity changes with time.
Term
Newton's Second Law
Definition
The acceleration of an object is directly proportional to the net force acting on it and is inversely proportional to it's mass.
Term
Force is expressed in
Definition
lbs or newtons
Term
Newton's Third Law
Definition
Action and Reaction: Whenever one object exerts force on a second object, the second object exerts an equal and opposite force on the first object.
Term
angular momentum
Definition
A measure of how much energy is stored in an object due to it's rotation and revolution. Depends on amount of mass, speed of rotation/revolution, and how spread out mass is.
Term
Newton's Law of Universal Gravitation
Definition
Objects attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Term
density
Definition
Total mass divided by total volume.
Term
Model
Definition
A hypothesis that has withstood observational or experimental tests.
Term
Parabola
Definition
An open curve formed by cutting a circular cone at an angel parallel to the sides of the cone.
Term
hyperbola
Definition
An open curve obtained by cutting a cone with a plane.
Term
Metal
Definition
All elements other than helium and hydrogen.
Term
solar nebula
Definition
The cloud of gas and dust from which the sun and rest of the solar system formed.
Term
protosun
Definition
The Sun prior to the time when hydrogen fusion began in it's core.
Term
protoplanetary disk
Definition
A disk of material encircling a protostar or newborn star.
Term
planet
Definition
An object orbiting a star that is held together by it's own gravitational force in a nearly spherical shape, that is able to clean it's neighborhood of debris, and is not the satellite of a larger body.
Term
planetesimal
Definition
Primordial asteroid-like object from which the planets accreted.
Term
protoplanet
Definition
The embryonic stage of a planet when it's growing because of collisions with planetesimals.
Term
accretion
Definition
Gradual accumulation of matter by an astronomical body, usually caused by gravity.
Term
Core-Accretion Model
Definition
Traditional theory of giant planet formation that begins with terrestrial planets slowly pulling abundant amounts of water, hydrogen and helium onto themselves.
Term
gravitational instability model
Definition
The theory of giant planet formation in which gases collapse together quickly.
Term
orbital inclination
Definition
Tilt or angle of an object's orbital plane around the sun compared to the ecliptic.
Term
crater
Definition
A circular depression on a celestial body caused by the impact of a meteoroid, asteroid or comet, or by a volcano.
Term
asteroid
Definition
Any of the rocky objects larger than a few hundred meters in diameter that orbits the Sun.
Term
asteroid belt
Definition
A 1.5 AU wide region between orbits of Mars and Jupiter in which most asteroids are found.
Term
meteoroid
Definition
A small rock in interplanetary space.
Term
comet
Definition
A small body of ice and dust in orbit around the Sun.
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