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Transcript
Charles Hakes
Fort Lewis College
1
Charles Hakes
Fort Lewis College
2
Chapter 10
Measuring the Stars
Parallax and Magnitudes
Charles Hakes
Fort Lewis College
3
Misc notes
• sunspots radiate less energy –
overall activity radiates more.
• magnetic fields disrupt convection
• remove folder debris
Charles Hakes
Fort Lewis College
4
Misc notes
• Problem 9.1
• Should say “Section 9.1” and NOT 16.1.
• And note that Mercury’s orbit is very
eccentric, so you can’t simply use the
semi-major axis for it’s distance at
perihelion.
Charles Hakes
Fort Lewis College
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Star Party
• Discovery Museum - tonight 6:30
Charles Hakes
Fort Lewis College
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Review
Charles Hakes
Fort Lewis College
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Which is the net result of the protonproton chain?
A) 4 protons = 1 helium 4 + 2 neutrinos + energy
B) 2 protons = deuterium + a positron + an antineutrino + energy
C) 4 protons = 2 helium-2 + 2 positrons + energy
D) 6 protons = 2 heliums + 3 positrons + 3 neutrinos + energy
E) only energy
Charles Hakes
Fort Lewis College
8
Which is the net result of the protonproton chain?
A) 4 protons = 1 helium 4 + 2 neutrinos + energy
B) 2 protons = deuterium + a positron + an antineutrino + energy
C) 4 protons = 2 helium-2 + 2 positrons + energy
D) 6 protons = 2 heliums + 3 positrons + 3 neutrinos + energy
E) only energy
Charles Hakes
Fort Lewis College
9
What evidence do we have for solar
convection?
A) sunspot polarity
B) the Zeeman effect
C) neutrino oscillations
D) granulation
E) nuclear fusion
Charles Hakes
Fort Lewis College
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What evidence do we have for solar
convection?
A) sunspot polarity
B) the Zeeman effect
C) neutrino oscillations
D) granulation
E) nuclear fusion
Charles Hakes
Fort Lewis College
11
Compared to the Earth, the Sun’s
average density is:
A) lower
B) about the same
C) much greater
Charles Hakes
Fort Lewis College
12
Compared to the Earth, the Sun’s
average density is:
A) lower
B) about the same
C) much greater
Charles Hakes
Fort Lewis College
13
If Vega is apparent magnitude zero,
and Deneb first magnitude, then
A) Vega is about 100x brighter than Deneb..
B) Deneb is one magnitude brighter than Vega.
C) Vega appears 2.5x brighter than Deneb.
D) Deneb must be a main sequence star, and Vega a giant.
E) Vega must be 2.5x more luminous than Deneb.
Charles Hakes
Fort Lewis College
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Chapter 10
Measuring the
Stars
Charles Hakes
Fort Lewis College
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Magnitude
• Historical Magnitude Scale
• Hipparcos/Ptolemy
• The brightest stars were “of the first
magnitude”
• Dimmer stars were second, third, etc.
magnitude.
• Dimmest stars were 6th magnitude
Charles Hakes
Fort Lewis College
16
Magnitude
• Modern Apparent Magnitude scale
• A difference of five magnitudes corresponds to
exactly a factor of 100 in brightness.
• One magnitude is a factor of 1000.2 = 2.511886
• Both negative and positive magnitudes are
allowed.
• Sun -26.8
• Sirius -1.4
• Faintest stars visible in Durango ~6.5
• Magnitudes don’t have to be integers.
Charles Hakes
Fort Lewis College
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More Precisely 10-1
More on the Magnitude
Scale
• Note relative
brightness on the
left, and magnitude
on the right.
Charles Hakes
Fort Lewis College
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Luminosity
• Luminosity - How much energy is coming
from the star.
• Solar constant (W/m2) measured above the
Earth’s atmosphere.
Charles Hakes
Fort Lewis College
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Figure 9.3
Solar Luminosity
Solar Constant is the
energy reaching the
Earth above the
atmosphere ~1400 W/m2
Charles Hakes
Fort Lewis College
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Luminosity
• Luminosity - How much energy is coming
from the star.
• Solar constant (W/m2) measured above the
Earth’s atmosphere.
• Energy from the sun decreases as 1/r2
• Stars show same decrease with distance.
Charles Hakes
Fort Lewis College
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Figure 10.4
Inverse-Square Law
Charles Hakes
Fort Lewis College
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Figure 10.5
Luminosity
• The more
luminous, distant
star appears the
same brightness
as the less
luminous, closer
star.
Charles Hakes
Fort Lewis College
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Luminosity
• Luminosity - How much energy is coming
from the star.
• Solar constant (W/m2) measured above the
Earth’s atmosphere.
• Energy from the sun decreases as 1/r2
• Stars show same decrease with distance.
• For stars, instead of measuring in W/m2,
use the “magnitude scale.”
Charles Hakes
Fort Lewis College
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Small Group Exercise
(Learning about the 1/r2 law.)
• Get in groups of ~four people.
• Assume each person has a superdeluxe flashlight left turned on by their
front door. It is facing the classroom.
• How much brighter does the closest
flashlight look than the farthest
flashlight?
Charles Hakes
Fort Lewis College
25
If Vega is apparent magnitude zero,
and Deneb first magnitude, then
A) Vega is about 100x brighter than Deneb..
B) Deneb is one magnitude brighter than Vega.
C) Vega appears 2.5x brighter than Deneb.
D) Deneb must be a main sequence star, and Vega a giant.
E) Vega must be 2.5x more luminous than Deneb.
Charles Hakes
Fort Lewis College
26
If Vega is apparent magnitude zero,
and Deneb first magnitude, then
A) Vega is about 100x brighter than Deneb..
B) Deneb is one magnitude brighter than Vega.
C) Vega appears 2.5x brighter than Deneb.
D) Deneb must be a main sequence star, and Vega a giant.
E) Vega must be 2.5x more luminous than Deneb.
Charles Hakes
Fort Lewis College
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Figure P.12
Parallax Geometry
Charles Hakes
Fort Lewis College
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Figure P.11
Parallax
Recall information
from the Prologue
Charles Hakes
Fort Lewis College
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Figure 10.1
Stellar Parallax
distance (pc) =
Charles Hakes
Fort Lewis College
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1
parallax angle
(arc sec)
Distance Analogy
• If the Sun is a marble…
• The Earth is a grain of sand 1 m
away.
• The solar system is ~100 m in
diameter
Charles Hakes
Fort Lewis College
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Distance Analogy
• If the Sun is a marble…
• The Earth is a grain of sand 1 m
away.
• The solar system is ~100 m in
diameter
• The next star is in Albuquerque!
Charles Hakes
Fort Lewis College
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Figure 10.2
Sun’s
Neighborhood
Charles Hakes
Fort Lewis College
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Parallax Measurements
• Earth-based measurements can typically
be made to 0.03”, or to a distance of ~30
parsecs (pc)
• Distances to several thousand stars are
known this way.
• The Hipparcos satellite extends the
distance to ~200 pc, so distances to nearly
one million stars can be measured with
parallax.
Charles Hakes
Fort Lewis College
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Figure 10.3
Real Space Motion - Barnard’s Star 22 years apart
• Nearby stars also show
proper motion, or
transverse velocities.
• Only a few hundred
show more than 1”/yr
Charles Hakes
Fort Lewis College
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If a star has a parallax of 0.05”, then its
distance must be
A) 5 light years.
B) 5 parsecs
C) 20 light years.
D) 20 parsecs.
E) 200 parsecs
Charles Hakes
Fort Lewis College
36
If a star has a parallax of 0.05”, then its
distance must be
A) 5 light years.
B) 5 parsecs
C) 20 light years.
D) 20 parsecs.
E) 200 parsecs
Charles Hakes
Fort Lewis College
37
What peak wavelength is emitted in
the core of the Sun (T=107K)?
A) .29 cm
B) .29 mm
C) .29 nm
D) .29 m
E) .29 km
Charles Hakes
Fort Lewis College
38
What peak wavelength is emitted in
the core of the Sun (T=107K)?
A) .29 cm
B) .29 mm
C) .29 nm
D) .29 m
E) .29 km
Charles Hakes
Fort Lewis College
39
Compared to the 5800K photosphere, sunspots
at 4500K emit what percent energy?
A) 26%
B) 36%
C) 46%
D) 56%
E) 66%
Charles Hakes
Fort Lewis College
40
Compared to the 5800K photosphere, sunspots
at 4500K emit what percent energy?
A) 26%
B) 36%
C) 46%
D) 56%
E) 66%
Charles Hakes
Fort Lewis College
41
Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
Charles Hakes
Fort Lewis College
42