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					The Stars, Galaxies, and
Light: The Astronomer’s Friend!
This is what you just saw. The prism
      refracts (bends) the light and
     divides it up into its component
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
Stars give off different types of light.
     We need to use these different
    types of light to study them. This
   involves using the electromagnetic
Mr. T gives off a different type of light
      too. What kind of light is this?
Mr. T gives off a different type of light
      too. What kind of light is this?

                      Visible     Infrared (FLIR)
                      Camera      Camera

Infrared!   Visible
Light is a form of electromagnetic
     radiation. It travels in waves,
  similar to the waves on the ocean.
Waves have certain parts to them. The
    crest is the highest part, and the
        trough is the lowest part.
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

Wave height
The wavelength of a wave is the
distance from one crest to the next
  crest, or one trough to the next
The Greek letter lambda () means



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


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 less waves, the
          lower the frequency.
The Greek letter nu () means
The frequency of a wave is measured
  in units called hertz (Hz). 1 hertz =
           1 cycle per second.
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.
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.
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?
The speed of light (c) is equal to the
  frequency () times the wavelength

How are energy, frequency, and
wavelength related? Go here to find
Here is the calculation for radio station
          KROQ at 106.7 MHz, or
      106,700,000 Hz = 106,700,000

   300,000,000 meters/second
   = 106,700,000 cycles/second
          X 2.81 meters
The light that you see and the
    radios stations described
  beforehand are all part of the
   electromagnetic spectrum.
Here is a NOVA tour of the
 electromagnetic spectrum.
So, How do we know what stars are
    made of is we can’t go to them
      to sample their chemistry?
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.
We then analyze the spectra, or
 colors, that a star emits (gives
         off) or absorbs.
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
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.
Go here for an example of various
    emission spectra for different
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.”
We can also use absorption spectra to
 determine the composition of a planet’s

“If the spectrum of the reflected light from a
    planet contains dark lines not contained in
   the sun’s spectrum, then these lines must be
       caused by substances in the planet’s
Sources of Continuous, Emission, and
           Absorption Spectra

Continuous: From a light bulb or hot metal
Emission: From light emitted from a hot gas
Absorption: From light that passes through a
cooler gas
             The Doppler Effect.

We can measure the amount of blue-shift or red-
     shift in a star’s spectrum to determine if a
    star is moving towards us or away from us.
            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.
            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.
              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
            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
              The Doppler Effect.

The spectra of a star reveal which direction a star
                       is moving.
             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.
Stars and Their
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.
What is the difference between astrology
               and astronomy?
Astrology is a belief that the stars and
   planets can influence human life in a
              mystical fashion.
Astronomy is a science that attempts to
    explain the Universe and everything
  within it. We are studying astronomy in
                  this class.
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
   The positions of constellations change
    throughout the year because of Earth’s
          revolution around the sun.
The Constellation Orion   The Constellation Scorpius is
is visible in Winter      visible in Summer
    The Apparent Magnitude is how bright a star
      appears from the Earth. The lower the Star’s
      apparent magnitude, the brighter the star is.
      Negative magnitudes are the brightest stars.
          For each increase 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     100 4000 160 630   250   100   40   16   6.3   2.5   1
             00       0
Star distances are measured in units
  called light years. A light year is the
    distance that light travels in one

  If light travels at 186,000 miles per
   second or 686,600,000 miles per
   hour, then how many miles is one
                light year?
Star Parallax, an apparent shift
   in star position, is a method
  of measuring distances to the
           nearest stars.
You use parallax every day.
   What do you use it for?
Distance in parsecs = 1 / parallax
1 parsec = 3.26 light years
1 parsec = 3.26 light years
   Stars have different mass, size, and
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
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
Relative Sizes of Stars
      Temperature and Color of Stars
Temp. (C)     Color          Elements     Class
> 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         Metals, H    Kiss
< 3,900       red            TiO2         Me
The Luminosity of a star is its actual

   Luminosity only depends on size
           and temperature.
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 star’s
      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
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 Cepheid’s
   apparent and absolute magnitude.
Life Cycles of Stars are shown
   with a Hertzsprung-Russell
        Blue Super            Red Super
        Giants                Giants

                     Main Sequence

           White Dwarfs
                              Red Dwarfs
We gauge the Life Cycle of Stars
  using the Hertzsprung Russell
          (H-R) Diagram
         Blue Super            Red Super
         Giants                Giants

                      Main Sequence

            White Dwarfs
                               Red Dwarfs
Another H-R Diagram
Click on this link to investigate
     the different life cycles of
   stars and how they relate to
         the H-R Diagram.
The stability of a star depends
    on the balance between
   gravity pulling inward and
 energy from nuclear reactions
       pushing outwards.
      Relativity and Black Holes
Albert Einstein was famous for his ideas on
The Stars Study Quiz
 The Stars Pre Quiz
 Please respond with
“Agree,” “Disagree,” or
“Don’t Know” on a half
    sheet of paper.
1. We know about stars by
  analyzing the light that we
2. Stars have life cycles,
   which last many many
3. The Universe is becoming
4. Stars are much closer to
   us than the planets are.
5. Hotter stars are red in