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Milkyway contains ___ stars
100 billion
Local Group
about 40 galaxies in galaxy cluster
Superclusters
clusters of galaxy clusters
1 AU
earth's average distance from sun
Light Year
distance light can travel in one year (9.46 tril km)
Observable Universe
14 billion light years
Big Bang
happened 14 bill years ago, avg. distance between galaxies increasing over time
Star Birth
gravity compresses material in cloud, center becomes hot/dense, undergoes nuclear fusion
Supernovae
massive stars dying in huge explosions
Elements in earliest universe
Hydrogen and Helium
Earth's Rotation
Rotates daily around axis, from west to east
Sun and Stars rise in the ___ , set in the ___
east, west
Ecliptic plane
flat plane defined by Earths orbit
Created sun centered solar system idea
Copernicus
Zodiac
constellations across ecliptic
Precession
gradual wobble that alters orientation of Earth's axis in space (every 26,000 years)
Zenith
point directly overhead
Meridian
half circle from north to south through the zenith
Angular size of moon
.5 degrees
Synchronous rotation
moon rotates on its axis the same amount of time it takes for it to orbit earth
New Moon
occurs when moon is between the sun and earth
Lunar Eclipse
moon must be full; earth lies between sun and moon
Solar Eclipse
moon must be new; moon lies between sun and earth
The altitude of celestial pole in sky is equal to
your latitude
Reason for seasons
tilt of Earth's axis causes sunlight to fall differently on Earth at different times of year
Lundar Phase
29.5 days
Apparent Retrograde Motion
apparent motion of a planet moving westward through the zodiac
Stellar Parallax
apparent shift in position of a nearby star based on position of orbit (doesn't happen if object is far away)
Reason for Greeks rejecting explanation for planetary motion
they couldn't detect parallax
Solar Calendar
what we use, synchronous with seasons
Geocentric model
Greek; placed Earth at center of universe
Ptolemaic Model
each planed moved around Earth on a small circle that turned about a larger one
Plato
heavenly motion must be in perfect circles
Kepler
discovered planetary orbits are ellipses
Keplers 1st Law of Planetary Motion
orbit of each planet around the sun is an ellipse with the sun at one focus (planets distance from sun varies during orbit)
Keplers 2nd Law of Planetary Motion
As a planet moves around its orbit, it sweeps out equal areas in equal times (planet travels faster nearer to the sun, slower further from sun)
Keplers 3rd Law of Planetary Motion
more distant planets orbit the sun at slower avg. speeds p^2=a^3
Tycho
observed first nova, saw it was further than moon
Objections to Copernicus' view of sun centered system
objects would fall away if Earth was moving, noncircular orbits meant heavens weren't perfect, no one could detect parallax
Aristotle
argued Earth centered universe
Speed
how far object will go in certain amt. of time
Velocity
speed and direction
Acceleration
change in velocity
Acceleration of Gravity (g)
acceleration of falling object, 9.8 m/s^2
Momentum
mass x velocity
Mass
amount of matter
Weight
mass x force; no gravity = no weight
Newton's 1st Law of Motion
an object moves at constant velocity if there is no net force acting upon it
Newton's 2nd Law of Motion
force = rate of change in momentum
F = M x A
Newton's 3rd Law of Motion
for any force there is always an equal an opposite reaction force
Conservation of Momentum
if there are no external forces, the total momentum of 2 interacting objects cannot change
Conservation of Angular Momentum
if there is no external torque, the total momentum of interacting objects cannot change
Angular momentum
mass x velocity x radius
Conservation of Energy
energy cannot appear/disappear out of nowhere, can only lose/gain energy by exchanging
Kinetic Energy
energy of motion, 1/2mv^2
Radiative Energy
energy carried by light
Potential energy
stored energy, gpe=m x g x h
Joule
standard unit of energy
Mass-Energy
E=MC^2
e = Amt of potential energy c = speed of light m = mass
Thermal energy
measures total kinetic energy of particles
Temperature
measures the average kinetic energy of particles in object
Universal Law of Gravitation
a) every mass attracts other mass through force of gravity
b) strength of gravitational force attracting any 2 objects is directly proportional to the product of their masses
c) inverse square law- strength of gravity between 2 objects decreases with the square of the distance between their centers
formula = F = G(m1m2/d^2)
Escape Velocity
amount of velocity required to escape earth's orbit (40,000 km/hr)
Moon's Tidal Force
difference in gravitational attraction from earth and moon on each side of the earth creates this
Power
rate of energy flow (watts)
Watt
1 joule/sec
White
colors in spectrum are equally mixed
Black
no light reflected
Diffraction Grating
glass etched with many closely spaced lines, produce spectrum
Speed (light)
wavelength x frequency
Frequency
cycles per second (Hz)
Light is an Electromagnetic wave
traveling vibrations of both electric and magnetic fields
Photon
light behaves as a wave and particle
Infrared
light with wavelengths longer than red light
Radiowaves
longest wavelength
Microwaves
light falling between infrared and radiowaves
UV rays
light with wavelengths shorter than blue
X Rays
shorter than UV rays
Gamma rays
shortest rays
Emission
light bulb emits visible light
Absorption
when you place your hand near bulb, your hand absorbs some light, then warms hand
Transmission
glass/air, forms of matter, can allow light to pass through
Reflection/Scattering
light can bounce off matter, either all in same direction, or random
Visible Light
what we can see, 400 nm to 700 nm
Atomic Number
number of protons in nucleus
Atomic Mass
combined number of protons and neutrons
Sublimation
solid to gas
Evaporation
liquid to gas
Ionization
stripping electrons from atoms
Pressure
force per unit area pushing on objects surface
Intensity
amount of light at each wavelength
Spectroscopy
process of obtaining a spectrum and reading the information it contains
Continuous Spectrum
broad range of wavelengths without interruption (rainbow)
Emission Line Spectrum
light is only emitted at specific wavelengths (bright lines against a black background)
Absorption Line Spectrum
specific light wavelengths are absorbed (dark lines over rainbow background)