Stars

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Stars
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Distances To The Stars

• Stars are separated by vast distances.
• Astronomers use units called light years to
  measure the distance of stars
• A light-year is the distance that light travels
  in a vacuum in a year
• Proxima Centauri, is the closest star to the sun.

Measuring_Distance_in_Space__The_Light_Year
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Parallax

• Astronomers have developed various methods of
  determining the distance of stars.
• The change in position of an object with respect
  to a distant background is called parallax.
• As Earth moves in its orbit, astronomers are able
  to observe stars from two different positions.
• Astronomers measure the parallax of nearby stars
  to determine their distance from Earth

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Properties of Stars

• Astronomers classify stars by their color, size,
  and brightness. Other properties of stars are
  chemical composition and mass.
• Color and Temperature a stars color indicates
  the temperature of its surface.
• The hottest stars appear blue
• The cooler stars appear red
• The spectrum of color in a star is from blues to
  greens to yellows and reds.

The_Color_of_Stars
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Brightness

• The brightness of a star as viewed from Earth is
  dependent on many factors such as color intensity
  and distance.
• Apparent Brightness is the brightness of a star
  as it appears from Earth.
• The apparent brightness decreases as its distance
  from you increases
• Absolute Brightness is how bright a star really
  is. The absolute brightness is a characteristic
  of the star and is not dependent on its distance
  from Earth.

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Composition

• Each star has its own spectrum.
• Most stars have a chemical makeup that is similar
  to the sun, with hydrogen and helium together
  making up to 96 to 99.9 of a stars mass.

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How Stars Form

• A nebula is a large cloud of gas and dust spread
  out over a large volume of space.
• Some nebulas are glowing clouds lit from within
  by bright stars.
• A star is formed when a contacting cloud of gas
  and dust becomes so dense and hot that nuclear
  fusion begins.

How_Stars_Form
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Life Cycles of Stars

• Adult Stars A stars mass determines the stars
  place on the main sequence and how long it will
  stay.
• The amount of gas and dust available when a star
  forms determines the mass of each young star.
• The larger the star the more energy produce.
• Since blue stars burn brightly, they use up their
  fuel quickly and are short lived.

The_Life_Cycle_of_Stars.asf
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The Death of a Star

• The dwindling supply of fuel in a stars core
  leads to the stars death as a white dwarf,
  neutron star, or black hole.

Dying_Stars_and_Conclusion.asf
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Groups of Stars

• Astronomers have determined that more than half
  of all stars are members of star systems.
• There are three basic kinds of star clusters
  open clusters, associations, and globular
  clusters.
• Astronomers classify galaxies into four main
  types spiral, barred-spiral, elliptical, and
  irregular.

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Expanding Universe

• The observed red shift in the spectra of galaxies
  shows that the universe is expanding.
• Astronomers theorize that the universe came into
  being in an event called the big bang.
• Dark matter can only be detected by observing its
  gravitational effects on visible matter.

Beyond_the_Milky_Way_and_Back_Into_Time.asf
Spin_Around_the_Solar_System__A__Look_to_the_Stars