day_02 - Reading assignment Cosmic Catastrophes Chapter 6...

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August 30, 2010 Reading assignment, Cosmic Catastrophes, Chapter 6 plus Section 5.1, Section 1.2.4 and Section 2.3 for background Last lecture posted as pdf on class web site Astronomy in the News? NASA consulted on the psychology of isolation on behalf of the trapped Chilean miners. Pic of the Day – some early water on Mars might not have been acidic. Note Mars is “bigger” than the Moon when viewed from close up.
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White Dwarf – dense core left behind by low mass stars (less than 8 solar masses) after red giant and planetary nebular phase. Essentially every white dwarf formed since beginning of the Galaxy is still here 10-100 billion of them (~ 100 billion stars total), but a few white dwarfs have blown up. Most are dim, undiscovered, see only those nearby, none naked eye Sirius, brightest star in the sky, has a white dwarf companion. Can’t see the white dwarf with the naked eye, too small, dim, but Sirius is easy if you look for it at the right time. Find Sirius for the extra credit sky watch project. White Dwarfs (Section 5.1)
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Discussion Point: White dwarfs have about the same mass as the Sun and about the same radius as the Earth. How does the gravity of a white dwarf compare to the Sun and the Earth, and why?
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What do we know about white dwarfs? Mass ~ Sun Most are single, 0.6 M (solar masses) Some in binary systems, higher mass Size ~ Earth ~1% radius of Sun Density = mass volume 10 6 grams c. c.
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