Ch 21 Stars, Galaxies, and the Universe

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Ch 21 Stars, Galaxies, and the Universe

• Electromagnetic Radiation energy that travels
  through space in waves. Visible light is an
  example. Spectrum the characteristic colors of
  visible light. (ROYGBIV)
• Telescopes device that makes distant objects
  appear to be closer.
• Optical telescopes collect visible light
• Refracting Telescope uses convex lenses to
  gather and focus light.
• Reflecting Telescope uses a curved mirror to
  collect and focus light. (Newton first)
• - Diagrams are in the book page 746-747

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• 2. Radio Telescope used to detect radio waves
  in space. Look like a big dish.
• 3. X-ray Telescope used for looking at
  radiation in space, black holes, etc.
• 4. Ultraviolet Telescopes used to look at UV
  radiation from stars and other objects.
• 5. Infrared Telescopes used to view heat energy
  in space stars, etc.
• Observatory building that contains one or more
  telescopes. Usually on a high mountaintop or in
  space.
• Ex. Mauna Kea Hawaii,
• Space Telescopes - The Hubble, The Chandra X-ray,
  and The Spitzer Space Telescope
• - Most radiation absorbing telescopes need to be
  taken outside the atmosphere because radiation is
  blocked by it.

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Star Characteristics Sec 21-2

• Stars-balls of hot gas that glow, THEY DO NOT
  BURN!
• Constellations groupings of stars that resemble
  pictures. Ex. Orion the hunter, Ursa Major (Big
  Dipper) the Big Bear, Draco the Dragon, Leo the
  Lion, Etc.
• Stars are classified according to color,
  temperature, size, composition, and brightness.
• Color/Temp. Blue is the hottest, followed by
  white, yellow, orange, and red is the coolest.
• Size the largest is a supergiant, then a giant
  or large, then a medium (our sun), then a dwarf,
  and the smallest is a neutron star.
• Composition most stars are 73 Hydrogen and 25
  Helium. Use spectroscopes to view this. Each
  gas has a specific spectrum like a finger print.

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• Brightness of a star depends upon both its size
  and its temperature.
• Apparent Brightness is how bright a star appears
  to be from the Earth.
• Absolute Brightness is the brightness of the star
  if it were a standard distance from the Earth.
• Measuring a stars distance can be done with
  parallax, which uses the apparent change in
  position of the star when you look at it from a
  different position.
• We use units called light years to measure
  distance. A light year is about 9.5 trillion km
  in length. Light travels at 300,000 km per
  second.
• Hertzsprung-Russell Diagram is a graph of stars
  according to temperature and absolute brightness.
  Most stars are Main Sequence stars and run from
  the upper left to the lower right on the graph.

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Lives of Stars Sec 21-3

• Nebulas large clouds of dust and gas spread out
  over a large area. Protostars are born here. A
  star is born when the gases becomes so dense and
  hot that nuclear fusion starts.
• Mass the amount of mass a star starts with will
  determine how long it exists and what it does.
  Small mass stars live longer, and large mass
  stars live shorter. The sun is average.
• When stars run out of fuel, the core shrinks and
  outer layers expand red giant or supergiant.
  Then depending on mass it can pop or go into a
  supernova (huge explosion).
• White Dwarfs are cores of stars that have just
  popped. Our sun will turn into a white dwarf.
• Neutron stars are cores of stars that have gone
  into supernova, they are much heavier and hotter.

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• Pulsars are neutron stars that are spinning and
  giving off radio pulses, sometimes hundreds of
  times per second.
• Black holes are objects with so much gravity that
  nothing can escape, not even light. For this
  reason it is very hard to detect a black hole.
  We must use indirect methods like watching a star
  that is close by, or by measuring x-rays coming
  from the hot gases that are being sucked in.
• Chandra X-ray telescope has been very helpful in
  studying black holes.
• Most astronomers theorize that at the center of
  most spiral galaxies there is a black hole that
  is causing the galaxy to spin.

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Galaxies and Systems Sec 21-4

• Our galaxy is the Milky Way. It got its name from
  the Greeks Galaxias Kylos which means milky
  circle. It represents the hazy band of light
  stretched across the evening sky.
• Most stars are in groups of 2 or more. (Binary)
• Eclipsing Binary stars have one star dimmer then
  the other, so it blocks light from the other star
  in the system, Algol is an example.
• Alpha Centauri is the closest star to our sun, it
  is 4.3 light years away and made up or 3 stars.
• In 1995 the first planet around another star was
  discovered. Since then we are up to about 260
  other planets going around other stars, most are
  all large gas giants like Jupiter and our other
  outer planet.

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• Star Clusters are larger groups of stars
• Open clusters are loose collections made up of a
  few hundred to a thousand or so.
• Globular clusters are larger groups more densely
  packed together.
• Galaxies are the biggest groups being made up of
  billions and trillions of stars. 3 types
• Spiral look like pinwheels, some stars are
  still forming. Ours is the Milky Way. Pg 771
  100,000 light-years across, the sun is on one of
  the spiral arms of the galaxy.
• Elliptical looks like an oval, no new stars,
  closely packed together.
• Irregular usually smaller in size and number,
  still forming new young stars.

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Expanding Universe Sec 21 - 5

• The Universe is everything that we know of.
• Big Bang Theory the universe formed in an
  instant, billions of years ago, in an enormous
  explosion. As the universe expanded it cooled
  and formed atoms. 200,000 years after the
  explosion stars started to form.
• Edwin Hubble discovered that all the galaxies in
  the universe are moving away from each other.
  This helped support the big bang.
• Cosmic Background Radiation left over thermal
  energy from the big bang.
• Age of the universe according to these things is
  about 13.7 billion years old.

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• About 5 billion years ago, a giant cloud of gas
  and dust collapsed to form our solar system.
  This cloud is called a solar nebula.
• The sun was formed first in the center.
• Then planetesimals formed in the rest of the
  solar system that would later become the planets.
• The inner planets formed with more of an
  atmosphere around them, but over time lost most
  of their gasses to the suns heat and gravity.
• The outer planets in contrast, were further away
  from the sun, so they kept most of their gases.
• Most astronomers believe the universe will likely
  expand forever. Recently we have seen an
  acceleration in expansion due to dark energy.
  Dark energy and dark matter make up most of the
  universe.
• Dark matter cant be seen, it gives off no
  electromagnetic radiation, but it has gravity.