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Astro 101 Exam 2 Questions and Correct
Answers
Revolutions in the solar system Ans: Mostly Counterclockwise-
comets can be both
Rotations in the solar system Ans: Mostly Counterclockwise.
Clockwise=Venus Between=Uranus
Milky Way rotation Ans: 200 km/s
Two clouds that are on adjacent circular orbits around the galaxy.
What happens as they orbit? Ans: The inside cloud will eventually
pass the outside one
Molecular Clouds Ans: Cool and dense-short lived-can collapse and
fragment
Cloud Core Ans: Contain a protostar-small and hot
Accretion disks Ans: dense, hot, short-lived
Protostar Ans: dense, compressed interior. stable structure due to
Hydrostatic Equilibrium: no more collapse when pressure matches
weight of star
Hydrostatic Equilibrium Ans: Weight of material above pushes in
an inward direction. gravity and pressure balance out
Solar Nebular Theory Ans: • An enormous cloud of dust and gas
collapses into multiple cores. • cores starts to form a disk around
a protostar. • Material in the disk clumps. • These clumps (also
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called cores) draw in gas, turn into planets. • The protostar grows
large enough to turn into a young star, blowing away the disk,
leaving the planets.
The temperature of the proto-Earth was about 600 K, thus the
Earth formed out of: Ans: All substances that can condense at
temperatures below 600 K.
The composition of the solar nebula is likely similar to: Ans: The
Sun
F=ma Ans: external forces F on an object is equal to the mass m of
that object multiplied by the acceleration
William Herschel Ans: Discovered- Uranus and 4 Moons, Infrared
Light • Telescopes made: >400 • Symphonies written: 24
Ole Romer Ans: Ole Romer- Measured speed of light- 131,000
mpsecond
Hipparchus Ans: First comprehensive star catalog, rated stars on a
six point scale of brightness--which we still use.
Apparent Magnitude Ans: - smaller numbers= brighter (m)
Luminosity vs Brightness Ans: • Brightness is apparent—what we
see. • Luminosity is energy output/second—an intrinsic (absolute)
measure
Absolute luminosity+magnitude Ans: Absolute luminosity is
defined as the same as apparent
Absolute magnitude (M) most negative= most luminous (brightest)
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Brightness = Luminosity / distance2 • BUT! Don't use magnitudes
in this equation • Use solar luminosities instead Ans:
Brightness=l/d^2
Black body/thermal radiation Ans: absorbs all incident
electromagnetic radiation The color of a black body is a quick
measure of its temperature. • red = ~3000 K • yellow = ~5500 K •
blue = ~30,000 K
Wien's displacement law Ans: states that the black body radiation
curve for different temperatures peaks at a wavelength inversely
proportional to the temperature.
Two stars same size and distance which is hotter Ans: Which peak
is higher
Which of these stars in
Orion is most luminous?
star m M distance
1 Rigel 0.18 -6.69 773
2 Betelgeuse 0.42 -6.02 643
3 Bellatrix 1.64 -2.72 242
4 Alnilam 1.69 -6.38 Ans: 1. Rigel- Most negative=most luminous
Two stars at the same distance, which is more
luminous? Ans: Whichever is putting out more light at all
wavelengths
© 2025 All rights reserved
Astro 101 Exam 2 Questions and Correct
Answers
Revolutions in the solar system Ans: Mostly Counterclockwise-
comets can be both
Rotations in the solar system Ans: Mostly Counterclockwise.
Clockwise=Venus Between=Uranus
Milky Way rotation Ans: 200 km/s
Two clouds that are on adjacent circular orbits around the galaxy.
What happens as they orbit? Ans: The inside cloud will eventually
pass the outside one
Molecular Clouds Ans: Cool and dense-short lived-can collapse and
fragment
Cloud Core Ans: Contain a protostar-small and hot
Accretion disks Ans: dense, hot, short-lived
Protostar Ans: dense, compressed interior. stable structure due to
Hydrostatic Equilibrium: no more collapse when pressure matches
weight of star
Hydrostatic Equilibrium Ans: Weight of material above pushes in
an inward direction. gravity and pressure balance out
Solar Nebular Theory Ans: • An enormous cloud of dust and gas
collapses into multiple cores. • cores starts to form a disk around
a protostar. • Material in the disk clumps. • These clumps (also
© 2025 All rights reserved
, 2 | Page
called cores) draw in gas, turn into planets. • The protostar grows
large enough to turn into a young star, blowing away the disk,
leaving the planets.
The temperature of the proto-Earth was about 600 K, thus the
Earth formed out of: Ans: All substances that can condense at
temperatures below 600 K.
The composition of the solar nebula is likely similar to: Ans: The
Sun
F=ma Ans: external forces F on an object is equal to the mass m of
that object multiplied by the acceleration
William Herschel Ans: Discovered- Uranus and 4 Moons, Infrared
Light • Telescopes made: >400 • Symphonies written: 24
Ole Romer Ans: Ole Romer- Measured speed of light- 131,000
mpsecond
Hipparchus Ans: First comprehensive star catalog, rated stars on a
six point scale of brightness--which we still use.
Apparent Magnitude Ans: - smaller numbers= brighter (m)
Luminosity vs Brightness Ans: • Brightness is apparent—what we
see. • Luminosity is energy output/second—an intrinsic (absolute)
measure
Absolute luminosity+magnitude Ans: Absolute luminosity is
defined as the same as apparent
Absolute magnitude (M) most negative= most luminous (brightest)
© 2025 All rights reserved
, 3 | Page
Brightness = Luminosity / distance2 • BUT! Don't use magnitudes
in this equation • Use solar luminosities instead Ans:
Brightness=l/d^2
Black body/thermal radiation Ans: absorbs all incident
electromagnetic radiation The color of a black body is a quick
measure of its temperature. • red = ~3000 K • yellow = ~5500 K •
blue = ~30,000 K
Wien's displacement law Ans: states that the black body radiation
curve for different temperatures peaks at a wavelength inversely
proportional to the temperature.
Two stars same size and distance which is hotter Ans: Which peak
is higher
Which of these stars in
Orion is most luminous?
star m M distance
1 Rigel 0.18 -6.69 773
2 Betelgeuse 0.42 -6.02 643
3 Bellatrix 1.64 -2.72 242
4 Alnilam 1.69 -6.38 Ans: 1. Rigel- Most negative=most luminous
Two stars at the same distance, which is more
luminous? Ans: Whichever is putting out more light at all
wavelengths
© 2025 All rights reserved
