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The Universe ppt

VIEWS: 194 PAGES: 44

									   A star is a large celestial body that is
    composed of gas and that emits light
   The sun is the star that is nearest the Earth
   Stars are formed from clouds of dust and gas,
    or nebulas, and go through different stages
    as they age
   A light year is the distance that light travels in
    one year
   Stars are measured in light years away from
    the Earth
   A star is a huge sphere of hot hydrogen and
    helium gas
   Stars get their energy from nuclear fusion
    reactions which take place in the core
   Fusion combines the nuclei of hydrogen
    atoms into helium nuclei
   Each time that two particles fuse, energy is
    released.
   Energy moves slowly through the layers of a
    star by a combination of radiation and
    convection.
   During convection, hot gas moves away from
    the star’s core
   During radiation, energy is transferred to
    individual atoms
   The atoms absorb energy and
    transfer it to other atoms in
    random directions
   Although the ancient Greeks noticed that
    stars had color and divided stars by
    brightness, astronomers couldn’t learn about
    stars until the optical telescope was invented.
   The telescope allowed astronomers to study
    stars in more detail for the first time.
   The brightness of a star depends on the
    star’s temperature, size, and distance from
    Earth
   The brightest star in the night sky is Sirius
   Sirius is only 8.7 light years away
   Stars produce wavelengths of electromagnetic
    radiation other than visible light
   Scientists use optical telescope to study the
    waves emitted from astronomical objects
   Earth’s atmosphere blocks the wavelengths
   A star’s color is related to its temperature
   Hotter objects glow with light that is more
    intense and cooler objects have less intensity.
   The sun appears yellow because the peak
    wavelength of the sun’s
    energy is near yellow on the
    spectrum
   Light can be separated into a spectrum
   The spectra of most stars contain dark lines.
   The dark lines are caused by gases in the
    stars absorbing the light.
   Astronomers can study the patterns of dark
    lines to figure out which elements are parts
    of the star.
   Stars may appear different from one another
    because they are at different stages in their
    life cycles.
   In a way that is similar to other natural cycles,
    stars are born, go through stages of
    development and eventually die.
   About 90% of all stars in our galaxy are in
    their midlife
   The sun formed from a cloud of gas and dust,
    or a nebula, when it collapsed inward and
    pulled by force of its own gravity
   As the nebula collapsed it began to spin
   The onset of fusion marks the birth of a star
   Once this process started in the core of the
    nebula, the star we call the sun was born.
   Fusion reactions in the sun’s core generate
    energy that produces an outward pressure
    that balances the inward force due to gravity.
   The sun is currently converting hydrogen to
    helium.
   Eventually the core will exhaust about 25% of
    the hydrogen and the fusion reactions will
    decrease
   When the fusion reactions decrease, the core
    will contract under the weight of its outer
    layers
   The sun’s outer layers will expand and the
    sun will become a red giant
   The star is red because the surface is
    relatively cool.
   When the core of a red giant depletes, it will
    contract further.
   The outer layers will expand and leave the
    star, making the remnants a white dwarf.
   A white dwarf is a small, dim, and vey dense
    star the size of Earth
   Massive stars develop hotter cores that create
    heavier elements through fusion.
   The formation of an iron core signals the
    beginning of a supergiant star’s
    death
   When the core collapses a huge
    bright explosion called a
    supernova results.
   The remnants of a supernova become a
    neutron star
   Neutrons are very small in diameter but are
    very massive
   Neutron stars can be detected as pulsars, or
    spinning neutrons stars that are sources of
    pulsating radio waves
   The neutron star can collapse further into a
    black hole.
   A black hole consists of matter so massive
    and compressed that nothing, not even light,
    can escape its gravitational pull
   Black holes can not be seen directly.
   The Hertzsprung-Russell Diagram (or H-R)
    shows the luminosity of a star with the
    surface temperature of the stars.
   Once a star is stable, it will appear on the
    diagonal which is called the main sequence
   The sun is currently a main sequence star
   A galaxy is a collection of millions to billions
    of stars
   The nearest galaxy is over a million light
    years away.
   Scientists can find more than 100 billion
    galaxies
   Galaxies contain millions to billions of stars
    bound together by gravity.
   Scientists do not expect to find other
    planetary systems within other galaxies
   Due to the distance to other galaxies, the
    likelihood of finding other planets is small
   Gravity holds galaxies together
   Without gravity, everything in space would
    spread out
   Due to gravity, new stars can be born and
    stars can die.
   Our solar system takes 226 million years to
    complete an orbit around our galaxy.
   Galaxies are grouped together and bound by
    gravity in clusters.
   The Milky Way is part of a larger group called
    the Local Group which has more than 30
    galaxies in it.
   Clusters of galaxies can form larger groups
    called superclusters
   Galaxies can be divided into three major
    types: spiral, elliptical, and irregular.
   The three types of galaxies have many stars,
    but differ in structure
   We live in the Milky Way Galaxy
   Our solar system is located within a spiral
    arm about 26000 light years from the center
    of the galaxy
   The Milky Way is a spiral galaxy
   The spiral arms of the galaxy has gas and
    dust which is called interstellar matter
   Elliptical galaxies have no spiral arms and are
    spherical or egg shaped
   They often have a reddish color which
    astronomers assume means they have older
    stars
   The third type is irregular because they lack a
    well-defined structure.
   Most irregular contain little interstellar matter
    but have large amounts of young stars
   When scientists observe distant galaxies, they
    are looking back in time.
   Scientists do not know what a galaxy looks
    like now, but by studying closer galaxies they
    can slowly piece together the puzzle of how
    galaxies evolve.
   Galaxies change over time.
   Quasar is a very luminous object that
    produces energy at a high rate
   They are thought to be the most distant
    objects in the universe
   Scientists assume they are black holes or
    could be young galaxies
   The gas, dust, and stars are constantly in
    motion.
   Galaxies consume their gas and dust by
    making stars.
   Galaxies also change as a result of collisions
   Galaxies are changing over time.
   The universe is everything physical that exists
    in space and time
   The universe consists of all space, matter,
    and energy that exist in the past or the
    future.
   Everything is part of the universe.
   It takes time for light to travel in space.
   The further an object is away the longer it
    takes for light to get there.
   We never see objects in space in present time
   We see the universe now as it was in the past.
   Most of the universe is empty space
   Space is a vacuum with no air and no air
    pressure
   If an astronaut did not have a suit on in
    space, he would not be able to breath
   Scientists used new tools and new techniques
    to study star and galaxies for clues to how
    the universe began.
   Scientists have been able to theorize that the
    universe formed during a cataclysmic event
    known as the big bang.
   The universe is expanding.
   The Doppler Effect is a change in the
    observed frequency of radiation when an
    object is moving.
   Based on the Doppler Effect, scientists believe
    that galaxies are moving away from each
    other.
   Expansion implies that the universe was once
    smaller.
   Long ago, the entire universe might have
    been contained in an extremely small space
   If time moves forward from that point, all of
    the matter in the universe appears to expand
    rapidly outward like a gigantic explosion.
   The big bang theory states that the universe
    began with a gigantic explosion 13 to 15
    billion years ago.
   Based on NASA, the universe is about 13.7
    billion years old
   According to this theory, nothing existed
    before the big bang.
   Scientists found a form of radiation in the sky
    but had no explanation for it.
   They believe the signal is the cosmic
    background radiation predicted by the big
    bang theory
   After the big bang, the universe was
    extremely hot and made up of pure energy.
   There was a period of rapid expansion that
    caused the energy to cool and parts of the
    atom to form
   The first stars were born 400 million years
    after the big bang.
   The big bang is constantly being tested when
    new discoveries are being made.
   There are many other theories about the
    beginning of the universe.
   Scientists use their increasing knowledge
    about the universe to hypothesize what might
    happen to the universe in the future
   Telescopes are very helpful in predicting the
    future
   The universe will keep expanding
   The expansion of the universe will approach a
    limit in size
   The universe will stop expanding and start to
    fall back on itself
   The future of the universe depends on mass
   When the universe collapses back on itself it
    will be called the big crunch
   New technology help scientists test theories
   Some interaction between matter can not be
    seen which is called dark matter
   Scientists use mathematics to build better
    models of the universe

								
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