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ASTR 1020 * Spring 2017
MW 5:30-6:45 pm
Stellar and Galactic Astronomy
• Your instructor: Ryan Norris
– Switched from Dr. Doug Gies
• Email: [email protected]
• Remember labs start week of Jan 23 (this week!)
• Please get a syllabus from me if you don’t have
one
• For now slides will be on
www.astro.gsu.edu/~norris/ASTR1020
– Up by tomorrow at 12PM
Pop Quiz 1-Results
• These count as bonus
– 0-50% correct→0.25 pts
– 50-80% correct → 0.5 pts
– 80-100% correct → 0.75 pts
– Added to your total score for the course (total is out of 100 pts)
• The Quizes (first one next Monday) will have
a similar format but more questions
– You might even see the same question!
• Class Average: 50% (6/12)
Pop Quiz Question
What we see visually as the surface of the Sun is
the:
A. corona
B. core
C. photosphere
D. chromosphere
Pop Quiz Question
What we see visually as the surface of the
Sun is the:
A. corona
B. core
C. photosphere
D. chromosphere
Pop Quiz Question
The temperature of the solar corona is
approximately
A.
B.
C.
D.
1,000,000 K
100,000 K
15,000 K
6,000 K
Pop Quiz Question
The temperature of the solar corona is
approximately
A.
B.
C.
D.
1,000,000 K
100,000 K
15,000 K
6,000 K
Solar Atmosphere:
Photosphere
opaque limit, 4400 K
(top), 6000 K (bottom),
effective temperature
~5800K, visible light
emission, ~500km thick
Chromosphere
hotter, 6000K (bottom)30000 K (top), avg=
10000-20000K, ultraviolet
emission, ~2500 km thick
Corona
*really* hot, 106 K, X-ray
emission
Solar wind
(extends through
Solar System)
All subject to “activity”
Pop Quiz Question
The temperature at the center of the Sun is
approximately
A. 6,000 K
B. 15,000,000 K
C. 15,000 K
D. 100,000 K
Pop Quiz Question
The temperature at the center of the Sun is
approximately
A. 6,000 K
B. 15,000,000 K
C. 15,000 K
D. 100,000 K
Pop Quiz Question
Sunspots appear dark because they are
A. cooler than their surroundings
B. hotter than their surroundings
C. obscured from our point of view
D. formed in the corona
Pop Quiz Question
Sunspots appear dark because they are
A. cooler than their surroundings
B. hotter than their surroundings
C. obscured from our point of view
D. formed in the corona
Pop Quiz Question
Sunspots,flares, prominences, and coronal
mass ejections are all caused by
A. neutrinos
B. magnetic activity on the Sun
C. the interaction of the Sun’s magnetic field and the solar
wind
D. electrical activity on the Sun
Pop Quiz Question
Sunspots,flares, prominences, and coronal
mass ejections are all caused by
A. neutrinos
B. magnetic activity on the Sun
C. the interaction of the Sun’s magnetic field and the solar
wind
D. electrical activity on the Sun
Pop Quiz Question
Nuclear fusion in the center of the Sun
produces energy by the following
reaction:
A. four H to one He
B. one H to four He
C. one He to one H
D. one H to one He
Pop Quiz Question
Nuclear fusion in the center of the Sun
produces energy by the following
reaction:
A. four H to one He
B. one H to four He
C. one He to one H
D. one H to one He
Pop Quiz Question
If energy production in the center of the Sun suddenly changed, which
evidence would astronomers notice first?
A. A change in visible-light emission
B. A change in neutrino emission
C. They would notice both at the same time
Pop Quiz Question
If energy production in the center of the Sun suddenly changed, which
evidence would astronomers notice first?
A. A change in visible-light emission
B. A change in neutrino emission
C. They would notice both at the same time
Pop Quiz Question
If the Sun’s core suddenly contracted (shrunk in radius) a little bit, what
would happen in the Sun?
A. The core would cool off and continue to shrink as its density
increased
B. The density of the core would decrease, causing the core
to coll off and expand
C. The core would heat up, causing it to radiate so much
energy that it would shrink even more
D. The core would heat up, fusion rates would increase, the
core would re-expand.
Pop Quiz Question
If the Sun’s core suddenly contracted (shrunk in radius) a little bit, what
would happen in the Sun?
A. The core would cool off and continue to shrink as its density
increased
B. The density of the core would decrease, causing the core
to coll off and expand
C. The core would heat up, causing it to radiate so much
energy that it would shrink even more
D. The core would heat up, fusion rates would increase,
the core would re-expand.
Solar Thermostat
Decline in core temperature
causes fusion rate to drop, so
core contracts and heats up
Rise in core temperature
causes fusion rate to rise, so
core expands and cools down
Pop Quiz Question
Hydrostatic equilibrium in the Sun means
the inward force of gravity is balanced by
the outward force of
A. pressure
B. light
C. electrons
D. anti-gravity
Pop Quiz Question
Hydrostatic equilibrium in the Sun means
the inward force of gravity is balanced by
the outward force of
A. pressure
B. light
C. electrons
D. anti-gravity
Pop Quiz Question
X is the amount of light received on Earth
whereas Y is the amount of light a star is
giving off.
A. Brightness:parallax
B. Parallax:luminosity
C. Brightness:luminosity
D. Luminosity:brightness
Pop Quiz Question
X is the amount of light received on Earth
whereas Y is the amount of light a star is
giving off.
A. Brightness:parallax
B. Parallax:luminosity
C. Brightness:luminosity
D. Luminosity:brightness
Pop Quiz Question
The star Racecar has a parallax 100 mas
while the star Kayak has a parallax of 50
mas. They are the same brightness. This
means that:
A. Kayak is twice as luminous as Racecar
B. Racecar is twice as luminous as Kayak
C. Racecar is four times as luminous as Kayak
D. Kayak is four times as luminous as Racecar
Pop Quiz Question
The star Racecar has a parallax 100 mas
while the star Kayak has a parallax of 50
mas. They are the same brightness. This
means that:
A. Kayak is twice as luminous as Racecar
B. Racecar is twice as luminous as Kayak
C. Racecar is four times as luminous as Kayak
D. Kayak is four times as luminous as Racecar
Pop Quiz Question
Kayak: parallax 50 mas
Racecar: parallax 100 mas
Distance=1/parallax
●
1/50 vs 1/100 → Kayak is twice as far away
●
Remember bigger parallax means closer!
●
Smaller parallax means further!
Brightness is the same but distance is twice as much
●
So Kayak has to be more luminous
Brightness is proportional to Luminosity/d^2
●
So if the distance is twice as much then in order for Brightness to be the same
Luminosity must be d^2 more or 2^2 more...4 times as bright
Pop Quiz Question
Kayak: parallax 50 mas
Racecar: parallax 100 mas
Distance=1/parallax
●
1/50 vs 1/100 → Kayak is twice as far away
●
Remember bigger parallax means closer!
●
Smaller parallax means further!
Pop Quiz Question
Brightness is the same but distance is twice as much
●
So Kayak has to be more luminous
Brightness is proportional to Luminosity/d^2
LK
BK
22
=
BR LR
12
LK
BK
4
=
BR LR
1
LK
1=
4
LR
1
LR
1
=
LK
22
4=LK/LR
Pop Quiz Question
A Blue star is hotter than a red star.
A. TRUE
B. FALSE
C. There is not enough information to answer this question
Pop Quiz Question
A Blue star is hotter than a red star.
A. TRUE
B. FALSE
C. There is not enough information to answer this question
Luminosity
HertzsprungRussell diagram
plots the
luminosity
versus
temperature of
stars
Temperature
Luminosity
In 1910
Ejnar
Hertzsprung and
Henry
Norris
Russell tediously
built the first HR
diagram for most
known stars (at
the time).
Positions of stars
in the HR diagram
are related to their
current state of
evolution.
Temperature
Extending the Cosmic Distance Scale
The problem with the classic
parallax distance method is
that it doesn’t reach far (< 200
pc).
The spectroscopic parallax
method doesn’t actually use
any parallax motion, it is
based on spectroscopy only.
It works till ~10000 pc.
We can estimate a star’s
luminosity if we know its
spectral type and luminosity
class
Extending the Cosmic Distance Scale
How to get a distance with the “spectroscopic
parallax” method:
1. Measure the star’s apparent magnitude m and
spectral classification
2. Use spectral classification to estimate luminosity
(absolute magnitude M) from HRD
3. Apply inverse-square law to find distance
Magnitude equation version:
m – M = 5 log d – 5 (will not be on the test)
Extending the Cosmic Distance Scale
Normal stellar parallax are limited to 500pc, but
spectroscopic parallax can extend the cosmic
distance scale to 10000 pc :
Stellar Properties Review
Luminosity: from brightness and distance
10-4 LSun - 106 LSun
Temperature: from color and spectral type
3,000 K - 50,000 K
Mass: from period (p) and average separation (a)
of binary-star orbit
0.08 MSun - 100 MSun
Lifetime
Sun’s life expectancy: 10 billion years
Life expectancy of 10 MSun star:
Until core
hydrogen
(10% of total) is
used up
10 times as much fuel, uses it 104 times as fast
10 billion years x 10 / 104 ~ 10 million years
Life expectancy of 0.1 MSun star:
0.1 times as much fuel, uses it 0.01 times as fast
10 billion years x 0.1 / 0.01 ~ 100 billion years
Main-Sequence Star Summary
High Mass:
High Luminosity
Short-Lived
Large Radius
Blue
Low Mass:
Low Luminosity
Long-Lived
Small Radius
Red
Luminosity
A
D
B
C
Temperature
Which
star is
most like
our Sun?
Luminosity
A
D
B
C
Temperature
Which of
these stars
will have
changed the
least 10
billion years
from now ?
Luminosity
A
D
B
C
Temperature
Which of
these stars
can be no
more than 10
million years
old ?
Star clusters =
groups of same
age stars
Open cluster: A few thousand loosely packed stars (Pleiades),
In the galactic disk, ~30 ly across, relatively young (< 5 billion years)
Globular cluster: hundreds of thousands stars in a dense ball
(M80), ~60-150 ly across, >10 billion years, in halo of the Milky Way
Massive
blue
stars die
first,
followed
by lower
mass
stars
(white,
yellow,
orange,
and red)
In HRD, stars die away
first at the top end
(massive stars) of main
sequence.
We can find the age of
a cluster by
determining the
turn-off point, which
corresponds to the
most massive stars still
on main sequence.
HR diagrams for two open clusters, showing the main
sequence turn-off at different ages.
Oldest
globular
clusters
are ~13
billion
years old
Pop Quiz Question
The spectral sequence ____ corresponds to
a temperature sequence of hot to cool
stars
A. OBAFGKM
B. OBFGAMK
C. OMAFGKB
D. MKGFABO
Pop Quiz Question
The spectral sequence ____ corresponds to
a temperature sequence of hot to cool
stars
A. OBAFGKM
B. OBFGAMK
C. OMAFGKB
D. MKGFABO
Pop Quiz Question
The star Canopus has spectral classification
A9II so its luminosity class indicates it is
a ___ star
A. main sequence
B. bright giant
C. subgiant
D. supergiant
Pop Quiz Question
The star Canopus has spectral classification
A9II so its luminosity class indicates it is
a ___ star
A. main sequence
B. bright giant
C. subgiant
D. supergiant
Pop Quiz Question
The Sun has a diameter over 100 times the
Earth’s
A. TRUE
B. False
Pop Quiz Question
The Sun has a diameter over 100 times the
Earth’s
A. TRUE
B. False
Pop Quiz Question
The apparent magntiude of the Sun is
A. Close to 5 as it is average in luminosity
B. Close to -27 as it is the brightest object in the sky
C. Close to -5 as it is average in luminosity
D. Close to 27 as it is the brightest object in the sky
Pop Quiz Question
The apparent magntiude of the Sun is
A. Close to 5 as it is average in luminosity
B. Close to -27 as it is the brightest object in the sky
C. Close to -5 as it is average in luminosity
D. Close to 27 as it is the brightest object in the sky
Pop Quiz Question
Which is the largest star:
A. a M7 I star
B. a F4IV star
C. a AIV star
D. a O2 II star
Pop Quiz Question
Which is the largest star:
A. a M7 I star
B. a F4IV star
C. a AIV star
D. a O2 II star
Pop Quiz Question
Globular Clusters are young and have
recent star formation
A. TRUE
B. FALSE
Pop Quiz Question
Globular Clusters are young and have
recent star formation
A. TRUE
B. FALSE