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Notes
Luminosity
Absolute magnitude - How bright a star actually is.
Apparent magnitude - How bright a star appears from Earth.
HR Diagram
A graph of stars' brightness (luminosity) and temperature.
shows color
shows the type of stars.
Hertzsprung-Russell Diagram
HR Diagram - Cheat Sheet
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Notes
Light
Energy from stars is transferred in the form of light.
And light moves in a wave pattern.
Wavelength of a Wave
Wavelength - Distance between tips of a wave.
(side to side)
Measured in nanometers (nm)
Frequency: How often the wave goes up and down
- # of waves that pass a point during a certain time period
- hertz (Hz) =1/s
Frequency and wavelength are inversely related.
-As frequency goes up wavelength goes down.
Frequency and energy are proportional. Higher frequency means
higher energy.
- Ex: High wavelength = low frequency = low energy
Electromagnetic spectrum
The entire range of frequencies and wavelengths.
The visible spectrum is the only part of the EM s
pectrum we can see, and is only one small part.
Travel through space at a speed of 300,000,000 m/s. (Speed of Light)
Light Year
Light year: the distance light travels in one year.
Visible Spectrum
The part of the spectrum we can see.
R O YG. B I V
Red Longer wavelengths (~700 nm) Lowest frequency Lowest energy
Viole Shorter wavelengths (-400 nm) Highest frequency Highest energy
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Notes
Spectroscopy Notes
The Light of Stars
what elements that make it up.
Spectroscopy - The study of light given off by elements.
-A spectral line is the unique combination of light that is
emitted/absorbed by each element. Spectral lines of elements are
similar to fingerprints
Spectra of Stars
Stars emit light across the whole visible spectrum, there is just
more light from the area that matches their spectra, or
"fingerprint". Each element absorbs part of it creating a “gap"
called a spectral line
Spectral Lines
When the elements absorb the light it makes these black absorption
lines
By seeing what parts of the spectrum are missing, we can determine
what elements are present.
Each element has a unique line combination.
Spectral Lines and Stars
By looking at the spectral lines of a star's light we can tell what
elements are in it.
-If it has all of the element's lines it has the element
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Notes
Doppler Effect
Doppler Effect: A change in the frequency of a moving wave relative to
an observer.
-Works for light and sound
Diagram: Sketch this Stationary source
Moving Source
Away: Waves "leaving" A are "expanded"
Wavelength long
Frequency lower
Sound pitch lower
Towards you: Waves near B are "compressed"
Wavelength short
Frequency higher
Sound pitch higher
Doppler Effect for Light
Movement causes the light waves to be bunched up.
This causes light to change color.
Luis Serrano P2
Notes
Big Bang Theory Notes
Expanding Universe
it has been observed that light from distant galaxies is redshifted,
meaning they are moving away from us.
Hubble's Law
All galaxies are moving away from us! And the farther away they are,
the faster their velocity appears to be…
Basically the universe is expanding and it's getting faster
Big Bang Theory
-universe is expanding
-trace back in time
-13.8 billion years ago everything was in a singularity: A single point
that held all of matter
-It started expanding and is still expanding today (evidence: red
shifted stars and galaxies)
-after initial expansion stuff cooled and hydrogen and helium formed.
-Once atoms formed, they could give off light and lots of heat!
leftover light can still be measured today.
Cosmic Background Radiation
-Light/Radiation given off by the first atoms created.
-Leftover microwave radiation from the Big Bang that can be detected
all around us that is still cooling.
-This sets the base temperature for space, 2.7 K (37° F)
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Notes
Kepler's 1st Law
-Johannes Kepler made the Three Laws of Planetary motion.
-They describe how planets move.
-1st Law - Planets move in an elliptical orbit around the sun.
Circular Orbit
-Circular orbits are based around a single central point (one focus).
-No matter where you are on the circle, you're always the same
distance from the center.
Elliptical Orbit
-Elliptical orbits are based around a single, non-central point called a
focus.
Parts of an Elliptical Orbit
-Ellipses have 2 foci that are the same distance from the center on the
major axis.
-For orbits, one focus is the sun.
-Perihelion - Point closest to the sun.
-Aphelion - Point farthest from the sun.
-An axis is an imaginary line down the center of an ellipse.
-Major Axis - The long one.
-Minor Axis - The short one.
- Semi-Major Axis is from center of the Major axis edge of ellipse.
- Semi-Minor Axis is from center of the Minor axis edge of ellipse.
Eccentricity
how elliptical an orbit is by the eccentricity (e). Eccentricity actually
tells us how different from a perfect circle the shape is.
-The higher the eccentricity = the more elliptical the orbit
-Eccentricity of 0 is a perfect circle (round)
-Eccentricity of 1 is a straight line (elliptical).
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Notes
Kepler's Second Law
Part 1: Planets move faster when they are closest to the sun
(perihelion point)
-due to the greater gravitational force.
-slowest at the farthest point from the sun (aphelion point)
Part 2: planets will cover the same area in the same given time
period.
-A and B took the same time to cover
-Segment B is equal in area to Segment A
Kepler's 2nd Law
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Notes
Kepler's 3rd Law
-Kepler's Third Law - The square of the orbital period of a planet is
directly proportional to the cube of its distance to the Sun.
-Basically the farther a planet is from the sun (a), the longer it will take
to orbit the sun (p).
Kepler's 3rd Law Equation
pa= a3
p = Orbital Period, time required for the planet to orbit the sun (Earth
years)
a = Distance to the Sun.
The semi-major axis of the elliptical orbit. (AU)
Calculating Period (p)
calculate how many years it takes something to orbit.
1. Find a
2. Find a?
3. Find Va3
Worked Example
A Planet Karl is 0.72 AU from the sun. Find how long it takes the
planet to orbit the sun.
1. Find a
a = 0.72
2. Find a3
0.72^3 = 0.373248
3. Find Va3
sqrt 0.373248 = 0.6109 years
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Notes
Gravity Notes
Force
-Gravity is a kind of force.
- Force is a push or a pull
-Vectors
-they have direction and magnitude.
-longer vector = greater force
-if all forces are not balanced the object will move.
Gravitational Force
-Gravitational force is the force that attracts all things with mass
toward each other.
-Objects in space would move in a line, but gravity makes them curve
and orbit around another object.
Mass and Distance
The gravitational force between objects depends upon their:
1. Masses (greater mass means greater force of gravity)
2. Distance apart (greater distance means less force of gravity)
Acceleration due to Gravity
All objects fall toward the earth at the same rate of acceleration,
regardless of their masses!
Weight Vs Mass
-
Weight is the force caused by gravity
Change depending on gravity
Mass is the amount of matter (atoms) in an object.
Stays the same