Download Stars: Intro & Classification Astronomy 1 — Elementary Astronomy LA Mission College

Stars: Intro &
Classification
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“The wonder is, not that
the field of stars of so
vast, but that man has
measured it.”
— Anatole France, The
Garden of Epicurus, 189
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Announcements
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SS Homework posted, due 11/19
Midterm — will debrief THURSDAY
Anybody see the….
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Last Class
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Solar System Topics
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
This Class
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Intro to Stars
Temperature, Color & Size
Stellar Classification
Intro to the HR Diagram
LT HR Diagram
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stars, Temperature and
Color
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Recall What a Star Is
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A sphere of hot gas
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Interior hot enough to undergo nuclear fusion
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mostly hydrogen & helium
most commonly H —> He
above 107 K = 10 million K (18 million °F)
Held together by gravity
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Fundamental Properties of Stars
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TEMPERATURE
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LUMINOSITY
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inherent brightness
amount of energy generated in the star and released as
electromagnetic radiation
SIZE
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color, spectral properties
Radius & Mass
DISTANCE
CHEMICAL COMPOSITION
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Luminosity
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Luminosity is a measure of the rate at which a star
puts out energy.
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Larger luminosity — appears brighter
measured in J/s or “watts”
sometimes relative to the Sun, in “solar luminosities” L☉
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L stands for luminosity, ☉stands for Sun
The Sun has a luminosity of 3.846×1026 W
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
HOW HOT IS THAT STAR?
Recall: Why Stars Shine
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Visible Sun is a hot
layer of gas
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about 5800 K (5525°C,
9980°F)
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not as hot as the center!
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Glows due to hot
material
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Other stars have similar
structure, range of
surface temperature
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Blackbody Radiation
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white light spectrum is
continuous
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no gaps between colors
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the hotter you heat
something, the bluer
it appears
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Thermal (heat related)
radiation from
(relatively) hot bulk
matter
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This is called blackbody
radiation
Astronomy 1 - Elementary Astronomy
LA Mission College
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Light diagnoses Temperature
Colder
feeling warm
faint reddish glow
brighter red glow
bright orange
very bright yellow
extremely bright
white
http://i302.photobucket.com/albums/nn114/fiddlegirl89_photos/Dave/DSC00596-1.jpg
bluish white
Warmer
Astronomy 1 - Elementary Astronomy
LA Mission College
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Spectrum of the Sun
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Stars emit light as blackbodies to a large extent.
Astronomy 1 - Elementary Astronomy
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Shape of Blackbody Spectrum
Astronomy 1 - Elementary Astronomy
LA Mission College
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Temperatue affects Color & Luminosity
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Hotter = greater
luminosity
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appears brighter
peak of curve higher
technically greater
luminosity per unit
surface area
Hotter = bluer
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peak of curve more to
left
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more blue mixed in with
red light
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
A lump of lead is heated to a high temperature.
Another lump of lead that is twice as large is heated to
a lower temperature. Which lump of material appears
bluer?
A. The cooler lump appears bluer
B. The hotter lump appears bluer
C. Both lumps appear the same color
D. Cannot tell which lump appears bluer
Astronomy 1 - Elementary Astronomy
LA Mission College
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When something is “red hot”, it is hotter than
something that is
A. blue hot
B. white hot
C. neither of these
D. both of these
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
SIZE, COLOR AND
TEMPERATURE
Recall
http://www.skinnerscience.com/Year
%2012,13/astrop3.jpg
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Hotter -> Brighter
Hotter -> Bluer
Bigger is also brighter!
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a star with a larger diameter has a greater
luminosity
Astronomy 1 - Elementary Astronomy
LA Mission College
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Analogy
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LED spotlight w/60
LEDs
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Total output ~1000
lumens
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each LED 1/60 of 1000
lumens
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comparable to 100-watt
bulb
~16.7 lumens
surface T gives you
“per-LED” luminosity
not total for star
Astronomy 1 - Elementary Astronomy
LA Mission College
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Stephan-Boltzman Law
is brighter than
is brighter than
is brighter than
could be brighter than
could be brighter than
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Star Yoda is a small blue star and star Chewbacca is a
large red star. Which is brighter?
(in terms of light output, not intelligence...)
A. Yoda
B. Chewbacca
C. They have the same brightness.
D. It’s not possible to tell.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Use the graph at right to determine which of the two
stars (A or C) has a higher luminosity?
h at right to determine which of the two stars (A
gher temperature?
tars have the same temperature.
ssible to determine this.
h at right to determine how the size of Star A
he size of Star C.
A. C.Star A
maller than Star
larger than Star C.
B. Star C
are the same size.
ssible to determine this.
C. The two stars have the same luminosity.
D. It is not possible to determine this.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Use the graph at right to determine which of the
Blackbody Radiation – Instructor’s Guide
following best describes how Star A would appear as
compared with Star B?
he graph at right to determine which of the following
describes how Star A would appear as compared with
B?
tar A would appear more red than Star B.
oth stars would appear more red than blue.
oth stars would appear more blue than red.
tar A would appear more blue than Star B.
one of the above.
he graph at right to determine which of the two stars
B) emits light with the longer peak wavelength?
tar A
tar B
A. Star A would appear more
oth stars peak emissions are at the same wavelength.
one of the above are possible.
red than Star B.
B. Both stars would appear the same color.
C. Star A would appear more blue than Star B.
he graph at right to determine which of the two stars (A
gives off more green light?
Astronomy 1 - Elementary Astronomy
LA Mission College
tar A
Levine F2015
Use the graph at right to determine which of the two
Blackbody Radiation – Instructor’s Guide
stars (A or B) is at a higher temperature?
he graph at right to determine which of the following
describes how Star A would appear as compared with
B?
tar A would appear more red than Star B.
oth stars would appear more red than blue.
oth stars would appear more blue than red.
tar A would appear more blue than Star B.
one of the above.
he graph at right to determine which of the two stars
B) emits light with the longer peak wavelength?
tar A
tar B
A. Star A is at a higher temperature
oth stars peak emissions are at the same wavelength.
one of the above are possible.
than Star B.
B. Both stars have the same temperature.
C. Star B is at a higher temperature than Star A.
he graph at right to determine which of the two stars (A
gives off more green light?
Astronomy 1 - Elementary Astronomy
LA Mission College
tar A
Levine F2015
Use the graph at right to determine which of the two
stars (A or C) is at a higher temperature?
h at right to determine which of the two stars (A
gher temperature?
tars have the same temperature.
ssible to determine this.
h at right to determine how the size of Star A
he size of Star C.
A. C.Star A
maller than Star
larger than Star C.
B. Star C
are the same size.
ssible to determine this.
C. The two stars have the same temperature.
D. It is not possible to determine this.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Use the graph at right to determine how the size of
Star A compares to the size of Star C.
e graph at right to determine which of the two stars (A
at a higher temperature?
rA
rC
two stars have the same temperature.
not possible to determine this.
e graph at right to determine how the size of Star A
es to the size of Star C.
r A is smaller than Star C.
A is smaller than Star C.
A. Star
r A is larger than
Star C.
stars are the same size.
Star A this.
is larger than Star C.
not possible toB.determine
C. The stars are the same size.
D. It is not possible to determine this
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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Know that different types of electromagnetic waves have different wavelengths
Know that visible light is a type of electromagnetic wave
The
Goals graph at right shows the blackbody spectra for
three
different stars. Which of the stars is at the
• Describe an object’s appearance given its blackbody curve
• Infer atemperature?
star’s color and temperature from its blackbody curve
highest
• Infer relative sizes of stars, when possible, from differences in their blackbody curves
Pre-activity Question
1) The graph at right shows the
blackbody spectra for three different
stars. Which of the stars is at the
highest temperature?
a) Star A
b) Star B
c) Star C
A. Star A
TUTORIAL GUIDE
1) [ Red ]
have difficulty relating light curves to physical appearance and, in particular,
Star
B
B.Students
struggle with the meaning of the word spectrum. This question introduces the concept of
relative intensity.
C. Star C
2) [ Violet, indigo, green, yellow, and red (i.e., all the colors except blue and orange). ]
We intentionally do not suggest that there is a simple mechanism for accomplishing this and
we avoid the concept of filters.
Astronomy
1 -a.Elementary
Astronomy
3) [ Figure
]
LA Mission College
Levine F2015
Spectral Classification
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
PRIMER ON SPECTRAL LINES
Spectroscopy
http://www.ibsen.dk/technology/images/design/
modules/spectrometer-sketch.jpg
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Spectroscope or spectrometer — astronomical instrument
that breaks light into its component wavelengths
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Where light is & is not present provides information
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what an object is made of
its physical properties
Astronomy 1 - Elementary Astronomy
LA Mission College
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Blackbody Spectrum
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continuous light spread across all colors
a continuous or continuum spectrum
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Emission Spectrumn
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light is present only in selected parts of the spectrum
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emission lines
bright bands on a black background
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Absorption Spectrum
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light is missing only in selected parts of the spectrum
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absorption lines
dark bands on a blackbody/continuous spectrum
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Atomic Structure and Energy Levels
http://odin.physastro.mnsu.edu/~eskridge/astr101/kauf5_20.JPG
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Electrons in an atom (this is Hydrogen) can be
modeled as being in specific “shells” or orbits around
the proton.
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Each shell has a specific energy level
Further out & higher numbered shells have a higher
energy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Atomic Transitions
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Electrons “prefer” to
be in lower energy
states
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can be kicked into a
higher energy by
absorbing a photon
with the right energy.
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right energy , right
wavelength
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E=hc/λ
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Atomic Transitions
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Electrons “prefer” to
be in lower energy
states
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Drops back down by
spitting out a photon
with the right energy
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right energy, right
wavelength
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E=hc/λ
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Emission Spectrum
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This is a Hydrogen Emission spectrum
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This pattern is specific to hydrogen, like a fingerprint
Each line is due to a specific transition of electrons
from a higher state to a lower state
Each element has a characteristic spectrum
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stellar Spectra
(visible light portion)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Spectral Class
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Recall red stars are
cooler than blue stars
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visual color isn’t very
precise
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Astronomers turned
to spectral properties
to classify stars
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detailed classification
based on line pattern
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Various schemes were
tried
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
PICKERING’S HAREM
&
THE HARVARD SPECTRAL CLASSIFICATION SCHEME
From Cosmos
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http://www.amazon.com/gp/product/B00K0CDNOI/
ref=avod_yvl_watch_now
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From “Sisters of the Sun” Episode 8
7:45 to ~16:00
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Harvard Computers
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The director of the Harvard Observatory from 1877 to
1919, Edward Charles Pickering hired women to
process astronomical data.
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They were cheaper than men
earned less than a clerical worker
Willamina Fleming had been his maid
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Harvard Computers
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"Pickering's Harem" or “the Harvard Computers” included several
now-famous astronomers
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Annie Jump Cannon,
Henrietta Swan Leavitt
Antonia Maury
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Modern Classification
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Harvard spectral sequence
Developed by Annie Jump Cannon
Characteristic absorption lines determine stellar class
Note: in Astronomy “metal” means anything “heavier” than
He
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Modern Classification
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Cecilia Payne (PayneGaposchkin) discovered this
was actually a temperature
sequence
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More precise than BB peak or
color
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Spectral Classification
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From hot to cool:
OBAFGKM
Each spectral class is further divided into 10 ranges
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according to temperature. 0 = hot, 9 = cool
therefore O0 is the very hottest, and O9 is slightly hotter than
B0 and M9 stars are very cool
This is still a temperature-based classification
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Star Rue is Type K, Star Peeta is Type B, Star Katniss
is Type F and Star Primrose is Type M.
Which star is cooler than Rue?
A. Peeta
B. Katniss
C. Primrose
D. None of them
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
You observe a very bright, bluish star. It’s spectral
classification is most likely ____.
A. B
B. G
C. M
D. More information is needed to determine this
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
H-R DIAGRAM
Spectral Class isn’t everything
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Spectral Class is not
sufficient to uniquely
identify a type of star
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The supergiant
Arcturus and the red
dwarf Proxima Centauri
are both Type M &
3500 K
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They are definitely not
identical!
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Hertzsprung and Russell
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html
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In 1911 Danish astronomer, Ejnar Hertzsprung, plotted the
absolute magnitude of stars against their color
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Independently in 1913 American astronomer Henry Norris
Russell plotted spectral class against absolute magnitude
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showed that the relationship between temperature and
luminosity of a star was not random
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The H-R Diagram
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H-R diagram plots Color and/or Temperature
against Luminosity and/or Absolute magnitude
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Any data plotted like this is an H-R diagram, as is a
theoretical version
The H-R diagram is one of the most important tools
in Astronomy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Main Sequence
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The long strip from
upper left to lower
right is called the
“Main
Sequence.” (MS)
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Stars spend most of
their existence on the
MS
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91% of nearby stars are
MS stars.
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MS stars are fusing H
into He in their cores.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Giants and Dwarfs
Astronomy 1 - Elementary Astronomy
LA Mission College
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WARM-UP QUESTION
Star A has an absolute magnitude of -8.1 and belongs
to spectral class B8. Star B has an absolute magnitude
of 11.2 and also belongs to spectral class B8. Which
star has the higher temperature?
A. Star A
B. Star B
C. They have the same temperature.
D. There is not enough information to determine
which star is hotter.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
LECTURE-TUTORIAL ON THE HR DIAGRAM
Star A has an absolute magnitude of -8.1 and belongs
to spectral class B8. Star B has an absolute magnitude
of 11.2 and also belongs to spectral class B8. Which
star has the higher temperature?
A. Star A
B. Star B
C. They have the same temperature.
D. There is not enough information to determine
which star is hotter.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
A red giant of spectral type K9 and a red main
sequence star of the same spectral type have the
same _____.
A. luminosity
B. temperature
C. absolute magnitude
Astronomy 1 - Elementary Astronomy
LA Mission College
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What Type of Star is Aldebaran?
A. Red Giant
B. Main Sequence
C. Supergiant
D. White dwarf
Astronomy 1 - Elementary Astronomy
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What Type of Star is Vega?
A. Red Giant
B. Main Sequence
C. Red Supergiant
D. White dwarf
Astronomy 1 - Elementary Astronomy
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WRAP-UP
Topic for Next Class
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Stellar Evolution
Measuring Distances (time permitting)
Astronomy 1 - Elementary Astronomy
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Reading Assignment
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Astro:8
Astropedia:13
Astronomy 1 - Elementary Astronomy
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Homework
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HW SS Posted, Due 11/19
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015