The Stars, Galaxies, and Universe

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The Stars, Galaxies, and Universe
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Light The Astronomers Friend!
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Light Maxwells Equations
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(No Transcript)
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This is what you just saw. The prism refracts
(bends) the light and divides it up into its
component parts.
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Light can also be diffracted (split) by
diffraction gratings, CDs, oily surfaces, and
soap bubbles.
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Before we can study stars, we must study the
light that comes from them. For, it is this light
that tells us everything that we want to know
about a star.
A nebula, the birthplace of stars
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Stars give off different types of light. We need
to use these different types of light to study
them. This involves using the electromagnetic
spectrum.
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Mr. T gives off a different type of light too.
What kind of light is this?
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Mr. T gives off a different type of light too.
What kind of light is this?
Infrared (FLIR) Camera
Visible Camera
Infrared!
Visible
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Light is a form of electromagnetic radiation. It
travels in waves, similar to the waves on the
ocean.
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Waves have certain parts to them. The crest is
the highest part, and the trough is the lowest
part.
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The amplitude of a wave is the distance from the
center of the wave to the crest (or trough). It
is ½ of the wave height. Amplitude is usually
measured in the base unit of meters.
Wave height
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The wavelength of a wave is the distance from one
crest to the next crest, or one trough to the
next trough.
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The Greek letter lambda (?) means wavelength.
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?
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The wavelength of a wave is measured in the base
unit of meters. Because the waves are usually
small, they are measured in µm (micrometers) or
nm (nanometers). 1 µm 1 X 10-6 m and 1 nm 1 X
10-9 m
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The frequency of a wave is a measure of how many
wave crests pass a certain point in a certain
time. The more waves, the higher the frequency.
The fewer waves, the lower the frequency.
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The Greek letter nu (?) means frequency
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The frequency of a wave is measured in units
called hertz (Hz). 1 hertz 1 cycle per second.
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KROQ radio broadcasts on an FM frequency of 106.7
MHz, KFWB radio broadcasts on an AM frequency of
980 KHz, and my radio control airplane works on a
frequency of 72.670 MHz.
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Electromagnetic waves are the result of
electricity and magnetism working together. The
Blue arrows show the electric field and the red
arrows show the magnetic field. The fields are
perpendicular to each other and to the direction
of the wave.
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Electromagnetic waves travel at the speed of
light, which is measured to be 3.0 X 108
meters/second or 186,000 miles/second or
669,600,000 miles/hour?
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The speed of light (c) is equal to the frequency
(?) times the wavelength (?).c ? x ?
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How are energy, frequency, and wavelength
related? Go here to find out.
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Here is the calculation for radio station KROQ at
106.7 MHz, or 106,700,000 Hz 106,700,000
cycles/second.300,000,000 meters/second
106,700,000 cycles/second X 2.81 meters
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The light that you see and the radios stations
described beforehand are all part of the
electromagnetic spectrum.
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Here is a NOVA tour of the electromagnetic
spectrum.
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So, How do we know what stars are made of is we
cant go to them to sample their chemistry?
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We use a method called spectroscopy, where the
spectra of a star is analyzed. We separate the
light coming from a star by using a tool called a
spectroscope.
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Examples of Continuous and Emission Spectra
Emission Spectra of an iPhone screen (photo
courtesy of Michael Greenberg, 2012)
Continuous Spectra of Sunlight (photo courtesy of
Michael Greenberg, 2012)
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We then analyze the spectra, or colors, that a
star emits (gives off) or absorbs.
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The spectra below is referred to as a continuous
spectrum. Light from all visible wavelengths is
being emitted.
A continuous spectrum is emitted from glowing
solids (a light bulb), glowing liquids (molten
iron), and the hot compressed gases inside stars
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The second spectra below is referred to as an
emission spectrum. Light from only certain
wavelengths is being emitted.
Each chemical element emits a different pattern
of light. We can analyze these patterns to
determine what chemical element(s) is(are) in a
star.
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Go here for an example of various emission
spectra for different gases.
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The third spectra below is referred to as an
absorption spectrum. Light from only certain
wavelengths is being absorbed by the cooler gas
it passes through.
By comparing emission and absorption spectra,
scientists can determine what elements are
present in the cooler gas that is absorbing some
of the light.
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We can also use absorption spectra to determine
the composition of a planets atmosphere.
If the spectrum of the reflected light from a
planet contains dark lines not contained in the
suns spectrum, then these lines must be caused
by substances in the planets atmosphere.
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Sources of Continuous, Emission, and Absorption
Spectra
Continuous From a light bulb or hot
metalEmission From light emitted from a hot
gasAbsorption From light that passes through a
cooler gas
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The Doppler Effect.
We can measure the amount of blue-shift or
red-shift in a stars spectrum to determine if a
star is moving towards us or away from us.
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The Doppler Effect.
You have experienced the Doppler Effect before
with police cars. If the police car comes toward
you, the higher pitch (shorter wavelength) you
hear.
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The Doppler Effect.
You have experienced the Doppler Effect before
with police cars. If the police car moves away
from you, the lower pitch (longer wavelength) you
hear.
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The Doppler Effect.
If a star is moving towards us, we will see a
blue-shift. This is because the wavelengths of
light are compressed into the shorter blue
wavelengths.
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The Doppler Effect.
If a star is moving away from us, we will see a
red-shift. This is because the wavelengths of
light are expanded into the longer red
wavelengths.
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The Doppler Effect.
The spectra of a star reveal which direction a
star is moving.
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The Doppler Effect.
A cosmological red-shift indicates that stars and
galaxies are moving away from us. As Mr. Auld
pointed out, this means that our Universe is
expanding, or moving outwards. WOW!
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The Doppler Effect.
Explain this sticker seen on the back of a car at
Caltech. What does it mean?
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Stars and Their Characteristics
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How many stars are in our galaxy? How many
galaxies are in our Universe? The stars that you
see with the naked eye are only within our Milky
Way Galaxy.
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What is the difference between astrology and
astronomy?
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Astrology is a belief that the stars and planets
can influence human life in a mystical fashion.
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Astronomy is a science that attempts to explain
the Universe and everything within it. We are
studying astronomy in this class.
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We call groups of stars constellations. These are
names given to groups of stars by ancient
astronomers. Constellations help us to find
stars. Go here for more information.
The Constellation Orion
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The positions of constellations change throughout
the year because of Earths revolution around the
sun.
The Constellation Scorpius is visible in Summer
The Constellation Orion is visible in Winter
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Stars that are near the North Star (Polaris) are
called Circumpolar Stars
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The Apparent Magnitude is how bright a star
appears from the Earth. The lower the Stars
apparent magnitude, the brighter the star is.
Negative magnitudes are the brightest stars. For
each decrease of 1 in apparent magnitude,
relative brightness increases by 2.5 times.
magnitude 0 1 2 3 4 5 6 7 8 9 10
Relative brightness 10000 4000 1600 630 250 100 40 16 6.3 2.5 1
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Star distances are measured in units called light
years. A light year is the distance that light
travels in one year.If light travels at 186,000
miles per second or 686,600,000 miles per hour,
then how many miles is one light year?
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Star Parallax, an apparent shift in star
position, is a method of measuring distances to
the nearest stars.
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Depth Perception Parallax Cartoon
Graphic sent by Veronica Marshall, 2012
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You use parallax every day. What do you use it
for?
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Distance in parsecs 1 / parallax angle
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1 parsec 3.26 light years
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1 parsec 3.26 light years
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Stars have different mass, size, and temperature.
Star Type Solar masses Solar radii
Sirius Main seq. 2.3 2.5
Rigel Blue super 20 36
Betelgeuse Red super 20 1,000
Aldebaran Red giant 5 20
Deneb Yellow Super 14 60
Capella Red Giant 3.5 13
Pollux Red Giant 4 8
Altair Main seq. 2 1.5

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Relative Sizes of Stars and YouTube Movie
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Relative Sizes of Stars
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Relative Sizes of Stars
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Relative Sizes of Stars
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SoWhat is the Biggest Star?
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Temperature and Color of Stars
Temp. (C) Color Elements Class
gt 30,000 Bluish white Ionized He Oh
9,500-30,000 Bluish white Neutral He Be
7,000-9,500 White Metals, H A
6,000-7,000 Yellow white Metals, H Fine
5,200-6,000 Yellow Metals, H Girl (or Guy)
3,900-5,200 Yellow orange Metals, H Kiss
lt 3,900 red TiO2 Me
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The Luminosity of a star (shaped like a sphere)
is its actual brightness.Luminosity only
depends on size and temperature.The formula for
luminosity isL 4?r2sT4where L is Luminosity
in Watts, ? is 3.1416, r is radius in meters, s
is Stefan-Boltzmanns constant (5.6703 x 10-8
(W/m2K4), and T is Temperature in Kelvin
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The Absolute Magnitude of a star is how bright
it would be if it were a distance of 10 parsecs
(32.6 light years) from Earth.This is different
from apparent magnitude because the apparent
magnitude does not account for the distance to
the star and the stars luminosity.
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Apparent Magnitude vs. Absolute Magnitude
Star Apparent Mag. Absolute Mag.
Aldebaran 0.87 -0.65
Algol 2.09 -0.15
Antares 1.06 -5.38
Betelgeuse 0.45 -5.09
Capella 0.08 -0.48
Polaris 1.97 -3.59
Procyon 0.41 2.62
Rigel 0.18 -6.75
Sirius -1.44 1.42
Spica 0.98 -3.55
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Cepheid Variable Stars can be used to measure
long distances to stars. Cycles of brightness
range from 1 to 50 days. A star with a cycle of
50 days would be brighter than a star with a
brightness range of 1 day. Astronomers can
calculate long distances by comparing a Cepheids
apparent and absolute magnitude.
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Life Cycles of Stars are shown with a
Hertzsprung-Russell Diagram
Blue Super Giants
Red Super Giants
Main Sequence
White Dwarfs
Red Dwarfs
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We gauge the Life Cycle of Stars using the
Hertzsprung Russell (H-R) Diagram
Blue Super Giants
Red Super Giants
Main Sequence
White Dwarfs
Red Dwarfs
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Another H-R Diagram
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Click on this link to investigate the different
life cycles of stars and how they relate to the
H-R Diagram.
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The stability of a star depends on the balance
between gravity pulling inward and energy from
nuclear reactions pushing outwards.
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Relativity and Black Holes
Albert Einstein was famous for his ideas on
relativity.
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The Stars Study Quiz
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The Stars Pre QuizPlease respond with Agree,
Disagree, or Dont Know on a half sheet of
paper.
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We know about stars by analyzing the light that
we see.
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Stars have life cycles, which last many many
years.
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The Universe is becoming smaller.
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Stars are much closer to us than the planets are.
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Hotter stars are red in color.