Stars

• A star is a great ball of gas formed by hydrogen and which is converted into helium through thermonuclear reaction called fusion
• Variable Star, A star that changes brightness. Its apparent magnitude is altered in any way from a perspective from Earth. These changes can occur in years or just fractions of seconds and can range from one-thousandth of magnitude to 20 magnitudes.
• Binary star, is a system of two stars that are gravitationally bound to and in around each other.
• Binary stars in the night sky are seen as a single object to the naked eye are often resolved using a telescope as separate stars, which are called visual binaries.
• Nova star, is an explosion from the surface of a white dwarf in a binary system. A nova occurs when the white dwarf, is a dense core of a once-normal star. When enough gas builds up on the surface of the white dwarf it triggers an explosion.
• The characteristics of a star:

  • The sun is an average sun
  • Not to hot and not to cold
  • Not to big small or big
• We can compare stars by color, temperature, size and brightness.
• Color:

  Stars can range to red, white, orange, yellow to blue
• Temperature:

  Stars range in temperature to 2000°C to 50000°C
• Temperature:

  2000°C = Red

  50000°C = Blue
•   Color       Temperature        Example

  Blue-white     12,000             Rigel,Spica

  White               11,000                 Vega

  White               10,000                Sirius

  Yellow              5000                Cepalla

  Orange           4000                Arcturus

  Red                  3000                Betelgeuse               
• Brightness is related to the distance from the earth and an age of a star.
• Life cycle of a star, The changes that a star goes through by how much mass the star has...
• Two types of  life cycles:

  • Average star - A star with relatively low mass
  • Massive star - A star with a relatively high mass
• All stars begin with a cloud of gas and dust called Stellar Nebula

  Gravity will cause the nebula to contract

  The nebula will break into smaller pieces will eventually form stars
• Protostars after a million years the gas forms into a small disk with a dense core.
• An average star(low mass star) is condensed in a nebula and begins a nuclear reaction that causes hydrogen to form heat and light.
• Red giant

  • Towards the end of the main sequence, a star begins to burn all of it’s hydrogen
  • The outer layers will collapse, become heated by the core, heated by the core and expand forming a red giant.
• The star quickly blow offs it’s steam forming a cloud around the star called a planetary nebula.
• White dwarf. When the star has burned all of its fuel it will collapse under the pressure of gravity. It forms a very small and dense.
• The iron core collapses on it’s self under the intense gravity at very high speed. The energy released is called supernova.
• Blackhole or Neotron Star. After the intense release of energy from the supernova a dense core(1 trillion times denser than the white dwarf)

  If the mass is too dense it will continue to collapse on itself forming a blackhole. The gravitational pull of a black hole is so great that light cannot escape.