# ASTR 1220 Final Exam

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 Author: jhl2011 ID: 273673 Filename: ASTR 1220 Final Exam Updated: 2014-05-07 20:54:11 Tags: astronomy final exam Folders: Description: Terms for the ASTR 1220 Final Exam Show Answers:

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1. rate of energy flow
power
2. watt
measure of energy flow (power) equal to 1 joule/s
3. emission
when a source produces light
4. absorption
when light is absorbed by matter (i.e. your hand absorbing light from a light bulb)
5. transmission
when light passes through a form of matter
6. reflection/scattering
when light bounces off something in the same general direction (reflection) or multiple random directions (scattering)
7. measure of light frequency
Hertz (Hz), cycles per second
8. blackbody
a perfect body that completely absorbs every kind of electromagnetic radiation and reradiates the energy as quickly as it absorbs it
9. The 3 properties of blackbodies are:
• 1. Every blackbody emits some radiation at every wavelength
• 2. A hot blackbody emits more radiation at every wavelength than a cool one
• 3. The peak wavelength of the radiation from a hot body is at a shorter wavelength than that for a cool body
10. The most common elements in the universe are:
• 75% H
• 24% He
• 1% other
11. continuous spectrum
a spectrum from an source like an ordinary light bulb that spans a broad range of wavelengths without interruption
12. emission line spectrum
the spectrum obtained from a thin, low-density cloud of gas that consists of thin emission lines that depend on the gas' composition
13. absorption spectrum
a continuous spectrum that is missing several colors that have been absorbed by a cloud of gas
14. Stefan-Boltzmann Law
• The total energy emitted per square meter of a blackbody is given by
• Therefore, temperature strongly affects the amount of energy emitted
15. Wien's Law
Hotter objects emit photons with a higher average energy (shorter wavelength), given by
16. A light source moving towards the observer causes
blueshift (shorter wavelengths)
17. A light source moving away from the observer causes
redshift (longer wavelengths)
18. luminosity
the power output of a star, or other blackbody
19. A nuclear fusion reaction of 1 kg of hydrogen produces
992.9 kg of helium, ~7.1 kg are converted into energy
20. ___% of the Sun's energy is generated in the _____ of the Sun
94% of the Sun's energy is generated in the inner 20% of the Sun
21. The closest star to our Sun is
Alpha Centauri (4.4 LY or 1.3 parsecs)
22. Brightness is given by
23. Kepler's First Law
Planets orbit stars in elliptical orbits, with the star at one of the foci of the ellipse
24. Kepler's Second Law
The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
25. Kepler's Third Law
• The squares of a planet's period of revolution is directly proportional to the cube of its semimajor axis.
• , where d = distance (AU), p=period (years)
26. The lifetime of our Sun is
10 billion years
27. The lowest mass a protostar can have before it becomes a brown dwarf is
0.08 MSun
28. Stars with a mass of _______ will leave behind planetary nebulae
<8 MSun
29. Stars whose core has a mass of _______ will form a white dwarf.
<1.4 MSun
30. Stars with a mass of ______ will die in a supernova.
8MSun<
31. Stars whose cores have a mass of _______ will form neutron stars.
1.4MSun < MCore < 3MSun
32. Stars with a mass of ______ who have cores with a mass greater than _______ will form black holes.
MStar > 20MSun, MCore > 3MSun
33. The definition of a black hole is...
an object whose escape velocity exceeds the speed of light.
34. Escape velocity is
• the velocity required for an object to break free from a body's gravity.