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Unformatted text preview: Chapter 11: Surveying the Stars STUDY COSMIC CONTEXT FIGURES THINGS TO REMEMBER Solar core releases (mass)energy by fusing H into He o E=mc2 o Mass of 4 protons > mass of He nucleus Two kinds of balance (solar thermostat) o Pressure must balance gravity o Energy from core must balance radiated energy Hydrogen in Suns core will eventually run out o Sun will not remain in balance forever HOW LUMINOUS ARE STARS? Luminosity- amount of power a star radiates (energy per second) Apparent brightness- amount of starlight that reaches Earth Luminosity passing through each sphere is the same Area of sphere: 4pi (radius) squared Divide luminosity by area to get brightness Brightness = Luminosity/ 4pi(distance) squared Luminosity= 4pi (distance) squared x (brightness) Parallax- the apparent shift in position of a nearby object against a background of more distant objects o Apparent positions of nearest stars shift by about an arcsecond as Earth orbits sun Parallax angle depends on distance Parallax is measured by comparing snapshots taken at different times and measuring the shift in angle to star Most luminous 10 6 Lsun Least 10-4 Lsun HOW HOT ARE STARS Every object emits Thermal radiation with a spectrum that depends on its temperature An object of fixed size grows more luminous as its temperature rises...
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- Fall '08