Stars

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Stars

• ES Chapter 30CPO Chapter 31

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Targets

• Interpret a Hertzsprung-Russell diagram
• On an HR diagram, where are the cool, dim stars?
• On an HR diagram, where are the hot, bright
  stars?
• Describe the life-cycle of stars.
• What process must start before a protostar
  becomes a main sequence star?
• What stage does a star enter when it uses up all
  of its Helium and why?
• Name and describe the different types of stars.
• What is true of all Main Sequence stars?
• What stage are Red Giants in?
• What changed to make you a White Dwarf?

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Lets Talk Lab!

• Each star is represented by a dot.
• The position of each dot on the diagram
  corresponds to the star's luminosity and its
  temperature
• What did you see?
• What are some trends?
• Were there any exceptions?

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Artistic Version
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Properties of Stars

• Size diameter of the sun 1,380,000 km
  (Earths diameter is about 15,000 km)
• Density sun is 1.4 times more dense than water
• Mass suns mass is 300,000 times more than
  Earth
• Color a stars color depends on the surface
  temperature.
• Hotter stars blue, Cooler stars red
• Sun 3000oC at surface

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Properties of Stars

• Composition stars are mainly hydrogen and
  helium.
• Composition affects the spectrum of a star.

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Properties of Stars

• Brightness can be measured in several ways
• Apparent magnitude how bright the star appears
  from Earth
• A 1st magnitude star is 2.5 times brighter than a
  2nd magnitude star.
• NOTE a bright star that is far away may appear
  dim

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Properties of Stars

• Luminosity actual brightness of a star
• Depends on size temperature
• Absolute magnitude apparent magnitude of a star
  if it were 32.6 light-years (10 parsecs) away
  from the sun.
• 1 parsec (pc) 3.26 light-years

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So Lets Review Star Life Cycles
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• Main sequence
• Energy from the burning of hydrogen in the core.
• Stars spend the largest portion of their lives
  burning hydrogen in their cores. This makes the
  main sequence the most populated grouping in the
  HR diagram.
• Red giants
• Energy from the burning of helium in the core and
  of hydrogen in the surrounding shell.
• Red giants are evolved stars (i.e., post-main
  sequence stars) of modest mass.
• Yellow and red supergiants
• Energy from the burning of helium, carbon,
  oxygen, or still heavier elements in their cores,
  and the burning of lighter elements in
  surrounding shells.
• Supergiants are evolved, massive stars.
• White dwarfs
• Energy from stored-up heat. Nuclear burning is
  extinguished.
• Black dwarfs
• Burned-out stellar cinders.

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DetailsLife of a Star

• BIRTH
• Starts as NEBULA (cloud of dust) gravity pulls
  particles together
• Becomes a PROTOSTAR (compacted dust that gives
  off heat)
• The protostar stage ends when the temperature
  inside is hot enough for FUSION to begin.

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Baby Pictures!
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DetailsLife of a Star

• TEENS MIDDLE AGE
• Spends the bulk of its time on the MAIN SEQUENCE
• Main sequence stars balance the pull of gravity
  with expansion from heat.

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Prom Pictures!
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DetailsLife of a Star

• OLD AGE
• Heat expansion overcomes gravity when the
  hydrogen in the core is used up
• A NORMAL main sequence star grows into a RED
  GIANT huge, cool star
• A MASSIVE STAR becomes a SUPER GIANT hundreds
  of times more luminous than a red giant. May be
  any color.

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DetailsLife of a Star

• RETIREMENT AND BEYOND
• When a star runs out of helium fuel, it collapses
  into a WHITE DWARF.
• Dwarf stars less luminous (absolute magnitude 1). Most are red, orange or yellow. Forces
  between electrons prevent collapse.
• Massive stars collapse to form neutron stars (2-3
  times the Suns mass, but only 10 km across)
• Forces between neutrons keep the star from
  collapsing

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Life Cycle of Stars

• The gasses around the core rebound off the
  neutron core to create a supernova explosion.
• Extremely massive stars collapse completely to
  become black holes. The gravity pull is strong
  enough to hold light.

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Supernova
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Targets

• Define constellations and describe how they
  change position in the night sky.
• Explain how distance, size, composition and
  brightness are used to classify stars and how
  these factors affect their appearance when viewed
  from Earth.

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Constellations

• Constellation group of stars that forms a
  pattern (total of 88)
• Circumpolar stars never set below the horizon and
  can be seen all year long
• (ex big dipper, little dipper, cassiopeia)
• Polaris North Star above North Pole

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Constellations

• Stars appear to move because Earth rotates
• Seasonal constellations stars that can only be
  seen during certain seasons (ex Orion, Summer
  Triangle)
• Stars in constellations move relative to each
  other, which causes the patterns to change over
  time.