2.1 Astro 1

# 2.1 Astro 1 - Astro 1 Section 1 Professor Brandt Monday...

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Astro 1 Section 1 Professor Brandt Monday February 1st 1999 Announcements: Lecture notes: Class 10 Moving on to stars Title is why does the Sun Shine? Will start giving the basic properties of the sun Sun is basically a big ball of gas Radius = 700 000 km = R(.) = 110 Earth radii Mass = 2x10 33 g = M(.) = 330 000 Earth masses How dense is the sun? on average density = mass/volume = 2x10 33 g/[4pi/3 * (7x10 10 ) 3 ] = 1.4 g/cm 3 cork = .24 g/cm 3 water = 1 g/cm 3 rock = 2-4 g/cm 3 earth = 5.5 g/cm 3 Temperature 5500 C surface. Hotter than typical fires on Earth However we know Sun is even hotter in center = 14 million degrees C. Energy output energy made in 1 second compared to a light bulb 100 Watts = 1x10 9 erg/sec sun radiates 4x10 33 erg/s about 4x10 24 light bulbs more than have been made in the history of people. How does the sun make all this energy? Fundamentally the sun shines because it converts matter into energy in its center through nuclear fusion famous Einstein equation E=mc 2 relates mass to the energy Energy = mass (speed of light) 2 speed of light = 3x10 10 cm/s Energy = mass (9x10 20 cm 2 /s 2 )

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• Spring '99
• Brandt

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