The Stars, the Galaxy, and the Universe

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Term Definition
Speed of Light 300,000 km/sec
What is Science? Universe operates according to patterns and rules. We can discover (or at least approximate) those rules. A method for learning about nature
Scientific Method Idea, Hypothesis, Prediction, Test
The cosmological principle "There is nothing special about our place in the universe.
Falsifiability The ability to, whether through observation or experiment, to test whether or not the idea is correct. "if it came out a certain way, [it would] force us to conclude that the idea is incorrect.
Theory A well-developed idea that is consistent with known physical laws and makes testable predictions about the world.
FiLCHeRS Falsifiable, Logical, Comprehensive – all evidence must be considered, Honest, Replecable, Sufficient
Rotation of Earth (direction?) Counterclockwise, 24 hours
The Celestial Sphere The projection of Earth's axes and the equator into space. Shows the NCP, SCP, Ecliptic and Celestial Equator
Celestial Poles North and South, directly above Earth's poles.
Ecliptic The Sun's path around the celestial sphere. 23.5 degrees from the equator
Celestial Equator The projection of Earth's equator into space
Circumpolar The location on the Earth (near the North and South poles) where no stars appear to rise or set.
Latitude The angle from the horizon to the NCP at a location.
Aberration of Starlight
Astronomical Unit Average distance to the Sun. Around 150 million km.
Why are there seasons? The Earth's axis is tilted. Not only does this mean certain areas get more light at different times of the year (separated by northern and southern hemisphere). Also, the angle of sunlight is closer to perpendicular (therefore more concentrated) in the su
Summer Solstice Sun is farthest north (June 21)
autumnal equinox The sun is on the equator moving southward (September 23)
Winter Solstice Sun is farthest south (December 22)
Vernal equinox Sun is on the equator moving northward. (March 21)
Waxing The moon is moving towards a full moon
Waning The moon is getting darker
New Moon Completely dark, cannot see the moon.
Gibbous When the moon is three quarters full (waxing or waning)
cresent When the moon is only one quarter full (waxing or waning)
copernicus Proposed that the sun is the center of the earth (heliocentric). 1545
kepler empirical rules to describe the orbits
Tycho Brahe Obtained detailed observations of the motions of the planets
Kepler's first law Planet orbits are ellipses with two foci. The sum is at one focus of the planet's elliptical orbit.
semimajor axis Describes the ellipses size. The longest length is twice the length of the semimajor axis.
eccentricity Describes how elongated the ellipse is and how far the foci are separated. The larger the eccentricity the more elongated the ellipse
Kepler's Second Law The law of equal areas. orbits sweep out equal areas in equal times. A planet will go fastest when closest to the sun.
Kepler's Third Law P^2=A^3. Where P is the period orbit in years and A is the length of the orbit in AU.
Sidereal period of the moon 27.3 days to orbit with respect to the stars. Time it takes for the moon to rotate around the earth once.
Synodic period 29.5 days. The amount of time it takes for the lunar cycle to repeat.
Solar eclipses happen at new moon. moon passes between the earth and the sun.
Types of solar eclipse Total: moon completely blocks the sun. Partial only part of the sun is blocked by the moon. Annular the sun appears as a bright ring surrounding the moon
lunar eclipse happen at full moon. earth is between the sun and the moon
Moon's orbit tilt 5.2 degrees with respect to earth's orbit around the sun.
Ptolomy Earth is the center of the universe
Galileo Gallilei Discovered concept of inertia. Acceleration due to gravity is constant. Looked at the sky with a telescope.
Isaac Newton Optics, Calculus, Mechanics, Gravitation, Planetary motions.
Newton's first law Law of Inertia
Newton's Second Law Unbalanced forces cause changes in motion. F=ma
Newton's Third Law For every force, there is an equal and opposite force. Same size, but opposite direction.
Gravitational Force equation F=G*m1*m2/r^2. Where G is the universal gravitational constant.
Uniform circular motion moving on a circular path at a constant speed.
Romer First measured the speed of light.
Electromagnetic waves a combination of electricity and magnetism caused by changing electric and magnetic fields
wavelength length between crests of a wave = speed/frequency
frequency number of waves that pass by each second
amplitude height of a wave
period time to complete one cycle of a wave.
The electromagnetic spectrum gamma rays (10^20) to AM radio waves (10^6). the visible spectrum ranges from violet (350 nm) to red (700 nm)
wave-particle duality light travels like a wave, interacts like a particle.
photon particle of light. carries energy/can have different amounts of energy. photons with high energy = high frequency light.
light emission an electron emiths a photon and drops to a lower energy state, losing energy. The photon's energy is equal to the energy difference between the two levels.
light absorption an electron absorbs a photon's energy to go to a higher level.
emission/absorbtion lines help determine the composition of stars.
Doppler effect the motion of a light source towards or away from us changes the wavelength of the waves reaching us. light from appraching objects is blue shifted (waves crowd together). light from receding objects is redshifted (waves are spaced far apart.)
Luminosity the amount of light leaving a source (hotter=more luminours)
brightness the amount of light arriving at a location (hotter=bluer). decreases as the distance from a light source increases. obeys the inverse square law.
blackbody radiation dense objects emit a blackbody (Planck) spectrum
Stefan's law F=sigma*T^4. sigma=stefan-boltzmann constant)
Flux defined via stefan's law and is the total amount of energy emitted per square meter every second.
Wien's law T=(2900micrometers*K)/wavelength. The peak wavelength of a blackbody is inversely proportional to temperature. hot=blue
wavelength related to energy lamda=(hc)/(E2-E1) where h and c are constants.
parallax change in position caused by a change in the position of the observer (only direct way to measure the distance to a star) Note: the greater the parallax, the smaller the distance. distance (pcs)=1/parallax(arcsec)
arcsec Arcsecond: 1/3600 of a degree
parsec (pc) 1pc = distance for parallax to equal 1 arcsec
How to determine the temperature of a star The color of the star determines the surface temperature. use Wien's law: T=2900micrometers*K/wavelength. Note: a hot star appears brighter through a blue filter (bB/bv>1), a cool star appears brighter through a visual filter.
Stellar Spectra The amount of light emitted as a function of wavelength. Takes the emission/adsorption lines and places them in an easy to see graph
Star classifications OBAFGKM. Absorption lines depend mainly on temperature. hottest stars: weak absorption by hydrogen/helium (type O). Middle: strong hydrogen absorption (type A). cool stars: absorption by heavy elements (type M) Sun is a G2
Stellar Composition Spectral lines determine the composition of stars. Sun: 74.5% hydrogen, 23.7% helium.
Sizes of Stars Stefan-Boltzmann law: L=(4*pi*R^2)*sigma*T^4. where sigma is the luminosity and L is total energy per second. Hotter star is more luminous
Stellar Masses Binary stars orbit a common center of mass. The less massive star moves faster in the larger orbit. d2/d1=m1/m2 or m2/m1=v1/v2. Kepler's third law: m1+m2=avg separation between stars^3/orbital period^3. Lowest Mass =0.08M.. Highest Mass=130 to 150m..
Binary Systems Used to determine the mass of a star. Two stars will rotate around a single, common point.
Visual Binary Systems can distinguish both stars visually
Spectroscopic binary pairs of Doppler-shifted lines trade places.
Eclipsing Binary The total light coming from the star system decreases when one star passes in front of the other.
H-R Diagram Hertzpring-Russell. Plot of Luminosity vs Temperature. Shows how stars change with time.
Main Sequence Runs from luminous/hot to low-luminosity/cool. line on the H-R Diagram that represents
Supergiants/giants Cool/very luminous stars
white dwarfs small, low-luminosity stars
photoshere visible surface of the sun. layer where light is emitted. avg. temp=5770 K
hydrostatic equilibrium outward pressure=inward force of gravity. rate of energy emitted=rate produced in the core.
Powering the sun fusion of hydrogen to helium in the central core. often called hydrogen burning.
p-p chain 1H+1H –> 2H+e(+)+v. positron annihilates: e(+)+e(-) –> 2 gamma rays. 2H+1H –> 3He+gamma. 3He+3He –> 4He+1H+1H.
Einstein's relativity E=mc^2
Second Law of Thermodynamics Hot regions transfer energy to cool regions.
Radiative Zone inner part of the sun. hotter photons move out form the core via radiative transfer.
convection zone past the radiative zone. rising/falling of hot/cool gas.
Surface of the sun radiation emitted into space. Energy takes 105 years to reach the surface
nutrinos emitted via hyrdogen fusion. light atomic particles with no charge/very weak interactions with matter.
Solar sound waves sound waves move through the surface of the sun. Doppler shifts give the speed of the wave motion
heliosesmology study of the sound waves which travel through the star, speeds depend on the sun's composition and the depth of the convection zone.
Chromosphere located above the photosphere. higher temp than the photoshpere. reddish emission-line spectrum.
Corona above the chromosphere. Very hot. emits x-rays
Solar Wind charged particles flowing away from the rotating sun through coronal holes where the magnetic field lines extend away from the sun.
solar rotation sun's axis is tilted 7.25 degrees. varies with latitude since the sun is made with gas.
sunspots cooler areas in the photosphere. caused by magnetic fields. 11-year sunspot cycle (part of 22 year magnetic cycle)
umbra dark patches of a sunspot or the dark spot during a solar eclipse
penumbra light areas surrounding umbra
solar maximum most sunspots and activity
maunder minimum distinct lack of sunspots between 1645 and 1715.
Prominences hot rising gas in the chromosphere constrained by magnetic fields
solar flares/coronal mass ejections (CME's) highly energetic, violent bursts and eruptions from the surface of the sun, where material leaves the surface in an eruption.

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