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Stars

Stars. What is a star?. The objects that heat and light the planets in a system A star is a ball of plasma held together by its own gravity Nuclear reactions occur in stars (H  He) Energy from the nuclear reactions is released as electromagnetic radiation. Characteristics of Stars.

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Stars

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  1. Stars

  2. What is a star? • The objects that heat and light the planets in a system • A star is a ball of plasma held together by its own gravity • Nuclear reactions occur in stars (H  He) • Energy from the nuclear reactions is released as electromagnetic radiation

  3. Characteristics of Stars • DISTANCE • Measured in light-years • The distance which a ray of light would travel in one year • About 6,000,000,000,000 (6 trillion) miles • 186,000 miles per second

  4. Characteristics of Stars • Magnitude (brightness) • A measure of brightness of celestial objects • Apparent magnitude • How bright a star appears to be from Earth • Absolute magnitude (luminosity) • How bright a star actually is

  5. Characteristics of Stars • Temperature & Color • The color of a star indicates the Temp of the star http://www.seasky.org/cosmic/sky7a01.html

  6. The Lives of Stars • A star’s life history depends on its mass. After a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole.

  7. The Lives of Stars

  8. Life Cycle of Stars • Begin their lives as clouds of dust and gas called nebulae • Gravity may cause the nebula to contract • Matter in the gas cloud will begin to condense into a dense region called a protostar • The protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins. • Begins the main sequence phase of the star • Most of its life is n this phase

  9. Life Cycle of Stars Life span of a star depends on its size. • Very large, massive stars burn their fuel much faster than smaller stars • Their main sequence may last only a few hundred thousand years • Smaller stars will live on for billions of years because they burn their fuel much more slowly • Eventually, the star's fuel will begin to run out.

  10. Life Cycle of Stars • It will expand into what is known as a red giant • Massive stars will become red supergiants • This phase will last until the star exhausts its remaining fuel • At this point the star will collapse

  11. Life Cycle of Stars • Most average stars will blow away their outer atmospheres to form a planetary nebula • Their cores will remain behind and burn as a white dwarf until they cool down • What will be left is a dark ball of matter known as a black dwarf

  12. Life Cycle of Stars • If the star is massive enough, the collapse will trigger a violent explosion known as a supernova • If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star

  13. Life Cycle of Stars • The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons. If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole

  14. Life Cycle of Stars http://www.seasky.org/cosmic/sky7a01.html

  15. Biggest Black Hole 3.5 Billion Light Years away 18 billion times the size of the sun!

  16. Black Holes • Gravity is so strong that not even light can escape! • Often at the center of galaxies! • A Galaxy is a huge group of stars, dust, and gas held together by gravity • Milky way is a spiral galaxy, but galaxies can also be irregular or elliptical in shape

  17. Black holes • http://youtu.be/cW7BvabYnn8

  18. Scientific Notation • Scientists use scientific notation (powers of ten) to describe really small numbers or really large numbers. • The decimal gets moved until there is only 1 number before the decimal • If you move the decimal to the right, the exponent is negative (RS= Right Subtract, Red Sox) • If you move the decimal to the left, the exponent is positive (LA= Left Add, LA Dodgers)

  19. Examples: • 0.0000467 = 4.67 x 10-5 • 0.000000089 = 8.9 x 10-8 • 5,677 = 5.677 x 103 • 2,340,000,000 = 2.34 x 109

  20. Expand the Numbers • 8.67 x 10-6 = 0.00000867 • 9.2 x 107 = 92,000,000 • 1.17 x 104 = 11,700 • 4.4 x 10-5 = 0.000044

  21. Practice Problem The sun takes about 220,000,000 years to revolve once around the center of the galaxy. Express this length of time in scientific notation. 2.2 X 108 years Scientific Notation

  22. Practice Problem The bright star Deneb is about 3,230 light-years from Earth. Express this number in scientific notation. 3.23 x 103 light-years Scientific Notation

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