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The Sun as a Star

The Sun as a Star. Susan Cartwright University of Sheffield. What do we know about the Sun?. Its size and its distance from us Its luminosity (energy generated per second) Its (surface) chemical composition and temperature How it generates energy Its (approximate) age

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The Sun as a Star

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  1. The Sun as a Star Susan Cartwright University of Sheffield

  2. What do we know about the Sun? • Its size and its distance from us • Its luminosity (energy generated per second) • Its (surface) chemical composition and temperature • How it generates energy • Its (approximate) age • from radioactive dating of solar system material • Its history and future • from our understanding of stars in general

  3. The Sun’s composition and temperature • The spectrum of the Sun tells us both its composition and its temperature

  4. How the Sun generates energy • Fusion of hydrogen to helium • How does this work? • He atom weighs slightly less than 4 H atoms (0.7%) • E = mc2 • How do we know? • Only mechanismthat lasts long enough! • We detect neutrinos

  5. Joe Morris, http://joemorris.mystarband.net/ The Sun as a Star

  6. How typical is the Sun? • Compare Sun with nearby stars • It is on the main sequence • It is brighter and more massive than average • but fainter and less massive than most bright naked-eye stars • It is not a binary • this is not rare, but probably more than half of all stars are binaries • It has planets • this is probably very common

  7. The Sun’s life and death: Youth • The Sun was born from a giant cloud of cool gas • this contracted under gravity • as it contracted it heated up • eventually the core reached 10 million degrees and hydrogen fusion began Most of following images taken from http://outreach.atnf.csiro.au/education/senior/astrophysics

  8. The Sun’s life and death: Youth

  9. The Sun’s life and death: Prime • The Sun’s main sequence lifetime is 10 billion years • Less massive stars live longer • More massive stars live less long • The Sun gets slightly brighter as it evolves on the main sequence • “faint young Sun problem” • Why didn’t early Earth freeze solid??

  10. The Sun’s life and death: Old Age • When the Sun has used up its core hydrogen, it will become a Red Giant • Red giants still use hydrogen as fuel, but outside the (pure helium) core • The helium core will get larger and hotter • Eventually it will reach 100 million degrees and helium fusion will begin • this is much less efficient and will not last as long

  11. The Sun’s life and death: Old Age

  12. The Sun’s life and death: Death • As helium fusion continues, the Sun will shed its outer envelope • the hot inner core will be revealed as a White Dwarf • about 0.6 times the Sun’s current mass, but only the size of Neptune

  13. The Sun’s life and death: Death

  14. The lives of other stars • Stars up to about 8 times the Sun’s mass live and die like the Sun • only more massive ones do it faster • Stars more than 8 times the Sun’s mass can fuse heavier elements • they are responsible for making most of the Periodic Table! • But they die young in a spectacular explosion called a Supernova

  15. The Life and Death of Stars Simulations from http://rainman.astro.uiuc.edu/ddr/stellar/beginner.html

  16. Planetary Systems

  17. Other Stars with Planets • 276 planets detected to date!

  18. Conclusions • The Sun is a star • a little brighter than most • a bit more massive than most • not a binary • Studying the Sun can tell us about stars • it is far closer than any other star and can be studied in much more detail • Studying other stars can tell us about the Sun • range of ages, masses and chemical composition available for study • planets are common – range of very different planetary systems can be studied

  19. Gliese 581 Probably like Venus Possibly habitable!

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