I. Stars

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I. Stars

• The Brightness of Stars
• -Star A hot glowing sphere of gas that produces
  energy by fusion.
• -Fusion The joining of separate nuclei. Common
  in nature, but not on Earth.

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1. Actual vs. Apparent Brightness

• Variables which affect a stars brightness
• Star size
• Distance from Earth
• Star temperature

• Apparent Brightness The amount of light received
  on Earth from a star.
• Actual Brightness How large and hot a star is in
  relation to other stars.

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Star Brightness

• Example (Fig. 20.1) Sirius has a greater
  apparent brightness then Rigel, even though Rigel
  is a much hotter and brighter star.
• Why?

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B. The Origin of Stars

• Nebula A large cloud of gas (helium and
  hydrogen) and dust which forms into a star.
• Dust and gas particles exert a gravitational
  force on each other which keeps pulling them
  closer together.

• Orion Nebula

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More Nebulas

• As the particles pull closer together the
  temperature increases.
• At 10,000,000o C fusion takes place and energy
  radiates outward through the condensing ball of
  gas.

• Another view of Orion

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C. Stellar Evolution

• Fusion uses up a stars hydrogen supply rapidly
  casing the core to heat up and the outer
  temperature to fall. (Life cycle of the star)
• Star expands and becomes a red giant

• Red Giant

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Stellar Evolution

• Core continues to heat and star expands to a
  super giant.
• As the core uses up its helium supply, the outer
  layers escape into space and the remaining core
  is white hot and called a white dwarf.

• White dwarfs

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More Stellar Evolution

• When no more material is left in the core it
  explodes into a supernova.
• Smaller stars become neutron stars and most
  massive will collapse into a black hole.

• Neutron Star

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Nothing (even light) can escape the gravity of a
BLACK HOLE
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Hertsprung-Russell Diagram
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Determining a Stars Temperature

• A stars temperature can be determined by its
  color.
• All objects will glow a different color when
  heated differently
• Colors hottest to coolest Blue/white ? yellow ?
  orange ? red.

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E. Hydrogen Fusion Energy of the Stars

• Stars have large amounts of hydrogen gas.
• Four hydrogen atoms fuse forming 1 atom of helium
• The mass of 4 hydrogen atoms is greater than the
  mass of 1 helium atom the excess mass is
  converted to a tremendous amount of energy.

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This hydrogen ? helium fusion can power a star
for billions of years
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1. Determining a Stars Composition

• Starlight is separated into a spectrum with a
  spectrometer
• A stars light has dark bands along the spectrum,
  these bands are caused by the absorption of
  certain wavelengths of light by specific gases in
  the star.
• Different bands show what elements are in the
  stars atmosphere.

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A stars spectrum
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F. Light-Years
Pierre Public Schools

• Light-year Distance light travels in one year.
  (Equal to about 9.5 trillion kilometers)
• Approximate distances
• -Sun to edge of solar system 5.5 light hours
• -Nearest star (Alpha Centauri) 4.3 light years
• -Center to edge of Milky Way 50,000 light years

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A. The Sun and You

• Our sun is a main sequence star according to the
  H-R Diagram.
• The actual brightness is average for a star of
  its average size.

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2. Layers of the Sun (Fig. 20.9)

• Dense inner core which is the site of hydrogen
  fusion.
• Radiation zone Energy bounces back and forth
  before escaping.
• Convections zone Cooler layer of gas that is
  constantly rising and sinking.

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Anatomy of Sun

• Photosphere Bright source of much of the light
  we see.
• Chromosphere Active layer which is home to many
  significant displays.

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Anatomy of Sun

• Corona Outer layer which is a gradual boundary
  between sun and space.

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3. Sunspots

• Sunspots Cool dark areas on the suns surface.
• -First discovered by Galileo
• -Not permanent featuresWill appear and disappear

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Cycle of Solar Activity

• Cycle of Solar Activity 11 year cycle which see
  number of sunspots change.
• Sunspot Maximum Time of many large sunspots.
• Sunspot Minimum Time of few sunspots.

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4. Prominences and Flares

• Prominence A huge arching column of gas.

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4. Prominences and Flares

• Solar Flares Violent eruptions near a sunspot
  which suddenly brighten and shoot outward at high
  speed.

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4. Prominences and Flares

• The interaction of solar flares with Earths
  magnetic field causes the aurora borealis/ aurora
  australis (Northern/Southern Lights)

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A. Earths Galaxyand Others

• Galaxy A large group of stars, gas, and dust
  held together by gravity.
• Milky Way Our galaxy which contains about 200
  billion stars and many nebulas

• Spiral Galaxies

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A. Earths Galaxyand Others

• Galaxies are grouped together in clusters.
• The cluster the Milky Way belongs to is called
  the Local Group.
• Three types of galaxies

• Cluster of galaxies

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Elliptical Galaxies

• Elliptical Galaxies Most common type of galaxy
  large three-dimensional football shaped galaxies.
• -Contain mostly older and dimmer stars.

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Spiral Galaxies

• Spiral Galaxies Circular galaxies that have arms
  curve outward from a central hub.
• Arms are made up of stars and dust

• Two spiral galaxies!!

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More Spiral Galaxies

• Barred spiral galaxies Have two spiral arms
  extending out.

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Irregular Galaxies

• Irregular Galaxies Come in many different shapes
  and are smaller and less common than elliptical
  or spiral galaxies.

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B. The Milky Way Galaxy

• 100,000 light years in diameter
• Our sun orbits the center of the galaxy once
  every 240 million years
• Probably a barred spiral galaxy
• Contains over 200 billion stars
• Its where I live!!!!!

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C. The Doppler Shift

• As waves (sound, light, etc.) move away, the
  lengths of the waves increases.

• Doppler Effect

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C. The Doppler Shift

• If a star is approaching the dark lines of its
  spectrum will move toward the blue part of the
  spectrum.
• If a star is traveling away (as most are) the
  lines will move toward the red part of the
  spectrum.

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C. The Red Shift

• The conclusion that the universe is expanding
  because of the red shift in light from galaxies.
• Quasars Star like objects at the outskirts of
  the universe which give off tremendous energy.
  ????