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  • MAGNITUDE (brightness)A measure of brightness of celestial objectsSmaller values represent brighter objects than larger values Apparent magnitudeHow bright a star appears to be from Earth Absolute magnitude (luminosity)How bright a star actually is
  • The color of a star indicates the T of the starStars are classified by TDecreasing T (bright to dim)O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]
  • Stars

    1. 1. Stars
    2. 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. 3. Characteristics of Stars
    4. 4. Characteristics of Stars
    5. 5. Characteristics of StarsClass Temperature Color O 20,000- 60,000 K Blue B 10,000 – 30,000 K Blue-white A 7,500 – 10,000 K White F 6,000 – 7,500 K Yellow-white G 5,000 – 6,000 K Yellow K 3,500 – 5,000 K Orange M 2,000 – 3,500 K Red
    6. 6. Hertsprung-Russell Diagram
    7. 7. Main Sequence stars ( young stars)• Main sequence stars are the central band of stars on the Hertzsprung-Russell Diagram. These stars energy comes from nuclear fusion, as they convert Hydrogen to Helium. Most stars (about 90%) are Main Sequence Stars. For these stars, the hotter they are, the brighter they are. The sun is a typical Main Sequence star.
    8. 8. Main Sequence stars ( young stars)DWARF STARSDwarf stars are relatively small stars, up to 20 timeslarger than our sun and up to 20,000 times brighter.YELLOW DWARFYellow dwarfs are small, main sequence stars.RED DWARFA red dwarf is a small, cool, very faint, main sequencestar whose surface temperature is under about 4,000 K.Red dwarfs are the most common type of star. ProximaCentauri is a red dwarf.
    9. 9. Giant and Supergiant Stars (Old, Large Stars )• RED GIANT A red giant is a relatively old star whose diameter is about 100 times bigger than it was originally, and had become cooler (the surface temperature is under 6,500 K). They are frequently orange in color. It is about 20 times as massive as the Sun about 14,000 times brighter than the Sun, and about 600 light-years from Earth. The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars.
    10. 10. Giant and Supergiant Stars (Old, Large Stars )RED SUPERGIANTSare supergiant stars (luminosity class I) of spectraltype K or M. They are the largest stars in the universein terms of volume. After the hydrogen in a stars corehas fused, stars with more than about 10 solarmasses become red supergiants for the duration oftheir helium-fusing phase. These stars have very coolsurface temperatures (3500–4500 K), and enormousradii. The radius of most red supergiants is between200 and 800 times that of the Sun. They last 10 to100 million years and are sometimes found inclusters. Luminosities can exceed 500,000 times thatof the Sun.
    11. 11. Giant and Supergiant Stars (Old, Large Stars )• BLUE GIANT A blue giant is a huge, very hot, blue star. It is a post-main sequence star that burns helium. SUPERGIANT A supergiant is the largest known type of star; some are almost as large as our entire solar system. Betelgeuse and Rigel are supergiants. These stars are rare. When supergiants die they supernova and become black holes.
    12. 12. Virtually Dead Stars• WHITE DWARF A white dwarf is a small, very dense, hot star that is made mostly of carbon. These faint stars are what remains after a red giant star loses its outer layers. Their nuclear cores are depleted. They are about the size of the Earth (but tremendously heavier)! They will eventually lose their heat and become a cold, dark black dwarf. Our sun will someday turn into a white dwarf and then into a black dwarf. the name white dwarf was coined by Willem Luyten in 1922.
    13. 13. Virtually Dead Stars• BROWN DWARF A brown dwarf is a "star" whose mass is too small to have nuclear fusion occur at its core (the temperature and pressure at its core are insufficient for fusion). A brown dwarf is not very luminous. It is usually regarded as having a mass between 1028kg and 84 x 1028.
    14. 14. Virtually Dead StarsNEUTRON STARA neutron star is a very small, super-dense starwhich is composed mostly of tightly-packed neutrons. It has a thin atmosphereof hydrogen. It has a diameter of about 5-10 miles(5-16 km) and a density of roughly 10 15 gm/cm3.PULSARA pulsar is a rapidly spinning neutron star thatemits energy in pulses.
    15. 15. SUPERNOVA in Latin it means NEW. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931. It can be triggered in two ways: by the sudden reignition of nuclear fusion in a degenerate star; or by the collapse of the core of a massive star. The explosion expels much or all of a stars material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.
    16. 16. PROTOSTARIt is a large mass that forms by contractionout of the gas of a giant molecular cloud inthe interstellar medium. The protostellarphase is an early stage in the process ofstar formation. For a one solar-mass star itlasts about 100,000 years. It starts with acore of increased density in a molecularcloud and ends with the formation of a TTauri star, which then develops intoa main sequence star.
    17. 17. Life Cycle of Stars
    18. 18.
    19. 19. QUESTIONS