Stars and Galaxies

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Stars and Galaxies
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BIG Idea

• The life cycle of every star is determined by its
  mass, luminosity, magnitude, temperature, and
  composition.

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• Much of our information about our galaxy and the
  universe comes from ground-based observations

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Hubble Space Telescope

• In orbit since 1990.
• Takes extremely sharp images from space.
• Hubble observations have led to numerous
  scientific breakthroughs, including rate of
  expansion of the universe.

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I. Characteristics of Stars

• Composition and Temperature
• What are stars made of?

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• mostly hydrogen (H)about 73 of a stars mass,
• approximately 25 helium (He),
• and the other elements in small amounts oxygen
  (O), carbon (C), nitrogen (N), silicon (Si),
  magnesium (Mg), neon (Ne), iron (Fe), sulfur (S)

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Spectral Types

• Spectroscope instrument used to determine
  chemical composition by separating light into
  different colors (wavelengths).

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Which stars are the hottest stars?
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• Blue stars are the hottest
• Red stars are the coolest

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B. Motion and Distance to the Stars

• Doppler Effect shift in wavelength of light
  source moving toward or away from an observer.
• Blue Shift shorter wavelengths, stars moving
  towards Earth
• Red Shift longer wavelengths, stars moving away
  from Earth

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• Distances between stars and Earth are measured in
  light-years.
• Light Year distance a light wave travels in one
  year
• (one light year 236,750,151 times around the
  Earth)

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C. Stellar Magnitude

• 1. Apparent Magnitude how bright a star
  appears from Earth (depends on light emitted
  and distance from Earth).

LOWER NUMBER BRIGHTER STAR
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2. Absolute Magnitude true brightness of a star.

• How bright a star would appear if seen from the
  same distance (32.6 light years)
• Most stars fall between -5 and 15
• Our sun is 5 middle of the range

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3. Luminosity energy output from the surface of
a star per second measured in watts.

• An Astronomer must know both the stars apparent
  magnitude and how far away the star is.
• The brightness depends on both a stars
  luminosity and distance from Earth.

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D. Classification of Stars

• H-R Diagram shows relationship between absolute
  magnitude and surface temperature of star
• the brighter the star, the hotter it is

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• Stars have a finite lifetime and evolve over time
• The mass of a star controls its evolution, length
  of lifetime, and ultimate fate
• As stars evolve, their positions on the
  Hertzsprung-Russell diagram move

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II. Stellar Evolution theory

• 1. Nebula stars start out as clouds of gas and
  dust
• 70 hydrogen
• 28 helium
• 2 heavier elements

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• Nebula in the
• Constellation Orion

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• Star Formation

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• Gravity pulls particles together, forming a
  sphere
• As density increases, gravitational attraction
  increases
• Gravitational forces cause denser regions of
  nebula to shrink
• As regions become smaller, they spin more rapidly

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• Think of an ice skater
• as he/she pulls his or her arms in closer, what
  happens to the rate of the spin?

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Protostar flattened disc of matter with a
central concentration (caused by shrinking,
spinning region)
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• Pressure and density build within the
  protostars center, causing temperature to rise
• Gas is so hot it becomes plasma (a fourth state
  of matter)
• Temperature continues to increase until it
  reaches 10,000,000ºC
• At this temperature nuclear fusion begins
• A star is born !

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2. Main Sequence Stars

• The second and longest stage in the life of a
  star
• Most stars fall within the main sequence band
• Our sun is a Main
• Sequence Star

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• During this main sequence stage, energy is
  generated in the core of the star as hydrogen
  atoms fuse to become helium atoms
• Fusion releases huge amounts of radiant energy

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3. Giants very large cool bright star

• Hydrogen starts to run out and the star expands
  greatly.
• Super Giants are very big Giants
• Our sun is 5 billion years old and has only
  converted 5 of its hydrogen to helium.

A Giant is 10x bigger than the Sun and a
Supergiant is 100x bigger
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4. White Dwarf final stage of a star

• Planetary Nebula expanding shell of gases
  shed by a dying star

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• Gravity causes the last of the matter in the star
  to collapse inward
• What remains is a hot, dense core of mattera
  WHITE DWARF
• White dwarfs shine for billions of years before
  they cool completely
• As white dwarfs cool they become fainter and
  fainter
• When they no longer emit energy, they become a
  black dwarf, a dead star

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Black dwarfs probably do not yet existWHY?
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Novas explosions that occur as a white dwarf
cools

• Supernova star that has such a tremendous
  explosion that it blows itself apart.

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Neutron Stars small but incredibly dense ball
of neutrons, formed from the collapsed core of a
supernova.

• One teaspoon of material from a neutron star
  would weigh 100 million tons on Earth.

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Black Holes hole left by the collapse of a
supernova.

• The gravity of a black hole is so great that not
  even light can escape from it.

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III. Star Groups

• A. Constellations patterns of stars in the sky
• there are 88 different patterns of stars
  recognized.

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B. Galaxies

• A galaxy is a large group of stars bound by
  gravity.
• typically 100,000 light-years wide
• contain billions of stars

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Types of Galaxies

• 1. Spiral central mass (nucleus) of bright stars
  with flat arms that spiral around it
• arms contain millions of young stars, gas, and
  dust.

Top View
Side View
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• 2. Elliptical nearly spherical with very bright
  centers no spiral arms
• No young stars, dust, or gas

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• 3. Irregular no particular shape.
• small and faint, with little gravitational
  attraction to organize it into a shape
• may also be unorganized due to the collision with
  another galaxy

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What type of galaxy do we live in?
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The Milky Way

• Spiral galaxy in which our solar system is
  located
• 100,000 light-years wide
• The sun is 30,000 light- years from the center
• The sun revolves around the center at 250 km/sec
• It takes 200 million years to make one
  revolution.

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IV. FORMATION OF THE UNIVERSE

• The Big Bang Theory most widely accepted theory
  explaining the formation of the universe.
• All matter and energy in the universe was once
  concentrated in a very small, very hot, very
  dense volume
• 12-15 billion years ago, the big bang occurred
• Matter and energy were propelled outward in all
  directions
• The universe began to E X P A N D

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• As matter and energy moved outward, the force of
  gravity had an effect
• Matter began to condense, forming the galaxies
• The galaxies continued to move outward, as they
  continue to do today

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V. The Sun

• There is nothing special about the Sun
• Its just close enough to Earth to give us light
  and warmth
• The Sun is similar to most other stars in our
  galaxy
• A large ball of gas made mostly of hydrogen and
  helium held together by gravity.
• The Sun is 300,000 times larger than Earth

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A. Structure of the Sun

• 1. Core
• The very hot (15,000,000ºC) gaseous center
• This is where nuclear fusion occurs
• FUSION is how the Sun makes its energy!

Hydrogen
Helium
Hydrogen
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2. The Inner Zones

• a. Radiative Zone
• Zone surrounding the core
• Heat energy moves by radiation
• b. Convective Zone
• Around the radiative zone
• Heat energy moves by convection

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3. The Suns Atmosphere (uppermost region of
solar gases)

• a. Photosphere light sphere
• visible surface of the Sun
• what we see

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• b. Chromosphere color sphere
• thin layer
• seems to glow with reddish light

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• c. Corona crown
• outermost layer of Suns atmosphere
• cannot be seen with naked eye, except during
  TOTAL solar eclipse
• huge cloud of gas that keeps the atomic particles
  from the surface from escaping into space

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• Solar winds
• the corona does not have a defined edge
• gas flows outward from the corona at high speeds,
  forming solar winds
• electrically charged atomic particles stream into
  space through holes in the corona
• flow to distant parts of solar system

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B. Solar Activity

• 1. Sunspots cooled regions within the
  photosphere
• Appear darker than the areas around them

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• 2. Prominences
• disturbances in solar atmosphere
• great clouds of glowing gases
• huge arches that reach high above Suns surface

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3. Solar Flares sudden violent eruptions of
electrically charged atomic particles.
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4. Auroras (aka Northern Lights or Southern
Lights)

• Magnetic storms in the Earths upper atmosphere
• Solar winds attracted to Earths magnetic poles
  by the Earths magnetosphere (space around Earth
  that contains a magnetic field)
• Electrically charged particles strike gas
  molecules in the upper atmosphere
• Green, red, blue, or violet sheets of light are
  produced
• Visible about 5 times per year, usually in polar
  regions

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VI. Our Solar System

• How many stars do we have in our Solar System?
• What bodies make up our Solar System?

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Formation of the Solar System

• Solar system the Sun and the planets and other
  bodies that travel around the Sun
• Solar Nebular Theory our best current idea for
  the origin of the solar system

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• Big Bang spread matter throughout universe
• Some matter gathered into clouds of dust and gas
• Cloud of gas and dust that eventually developed
  into our solar system is called the SOLAR
  NEBULA
• Solar nebula was larger than our solar system is
  now
• Heat and pressure from force of gravity caused
  center of solar nebula to become hotter and denser

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• While the Sun was forming in the center of the
  solar nebula, planets were forming in the outer
  regions
• Planetesimals (small bodies of matter within the
  solar nebula) joined together through collisions
  and the force of gravity to form larger bodies
  called protoplanets
• Protoplanets then condensed into existing planets
  and moons

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• The four protoplanets closest to the Sun became
• Mercury
• Venus
• Earth
• Mars

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• The next four protoplanets became
• Jupiter
• Saturn
• Uranus
• Neptune

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