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Stars

Stars. Properties of Stars. Astronomers classify stars by their color, size, and brightness. Other properties 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

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Stars

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  1. Stars

  2. Properties of Stars Astronomers classifystars by their color, size, and brightness. Other properties 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 indicates the temperature Red – toaster element Blue – welding torch

  3. Brightness Dependent on factors such as color intensity and distance. Apparent Brightness – is the brightness of a star as it appears from Earth. Does change with distance Luminosity (Actual brightness) – Energy per second being emitted Does NOT change

  4. Composition 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 star’s mass.

  5. Size and Mass of Stars Size is measured using luminosity and temperature Mass was not possible until the discovery that over half the stars we see are binary stars. Binary stars are two single stars orbiting each other. By knowing the size of the orbit and the time to complete it, calculating mass could be done.

  6. Task # 6 Copy and Answer the following questions: How would you explain luminosity to a friend? Which two factors explain why one star may appear to be brighter than another? Stars differ in color. How can color reveal the temperature of a star? Why is it said that a Sun is so similar to other stars of similar mass? How is the size of a star calculated? How is the mass of a star calculated?

  7. How Most Stars Form… • Stage 1 – The birth of a star (nebula) • Stage 2 – Yellow star • Stage 3 – Red Giant • Stage 4 – White Dwarf • Stage 5 – Red Dwarf

  8. How Stars Form The Birth of a Star – Formed when a contracting cloud of gas and dust from a nebula becomes so dense and hot that nuclear fusion begins. Some nebulas are glowing clouds lit from within by bright stars. The Yellow Star – Helium accumulates at the core while consuming hydrogen. How_Stars_Form

  9. Life Cycles of Stars The Red Giant – Gas is to a car as Hydrogen is to a Star. When it is used up, the star cannot produce any more light energy. The core contracts and star expands. Turns red as it cools. 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.

  10. The Death of a Star White Dwarf - A dwindling supply of fuel in a star’s core. Black hole has a gravitational pull so strong that light waves cannot escape the gravitational pull. Black Dwarf – Is cool enough that no light is emitted. Dying_Stars_and_Conclusion.asf

  11. Recapping the Evolution of Stars • Large clouds of gas and dust (aka inter-stellar material) • Gravity pulls “inter-stellar” material together • Accumulating gas causes temperature to rise. • Fusion (change of hydrogen into helium) occurs at 10 000 000 C. • Star turns on • Energy release balances with gravity to keep star stable • Life of the star depends on the mass • Stable Star = Main Sequence Star • Three Types of Main Sequence Stars

  12. The Inter-Stellar Material The ‘empty’ space between the stars…. • Stellar Winds – Particles that are emitted from a star • Planetary Nebula – A fuzzy object that was once a Red Giant • Supernova – Exploded Red Super giant

  13. Formation of the Solar System • The theory the astronomers currently have about how our stars and planets formed is called the Solar Nebula Theory. • Inner planets (Mercury, Venus, Earth Mars) became rocky because their gravity could not hold the hot atmosphere from the Sun’s radiation. • Outer planets (Jupiter, Saturn, Uranus, Neptune, and Pluto) kept their gas as they were further away from the heat.

  14. Review Questions • Which two factors explain why one star may appear to be brighter than another? • Stars differ in color. How can color reveal the temperature of a star? • How is the size of a star calculated? • How would you explain luminosity to a friend? • Why is gravity so important in a star’s life cycle? • In your text Pg 484 #1 – 6

  15. Before you go… • Describe to a classmate the evolution of a main sequence (medium mass like our Sun) star from its birth to its death. • Describe the solar nebula theory of star formation

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