stars: intro & classification...astronomy 1 - elementary astronomy la mission college levine...
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Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Stars: Intro & Classification
Astronomy 1 - Elementary Astronomy LA Mission College Levine 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
• 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
• Solar System Topics
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Intro to Stars
• Temperature, Color & Size
• Stellar Classification
• Intro to the HR Diagram
• LT HR Diagram
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Stars, Temperature and Color
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Recall What a Star Is
• A sphere of hot gas
• mostly hydrogen & helium
• Interior hot enough to undergo nuclear fusion
• 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
• TEMPERATURE
• color, spectral properties
• LUMINOSITY
• inherent brightness
• amount of energy generated in the star and released as electromagnetic radiation
• SIZE
• Radius & Mass
• DISTANCE
• CHEMICAL COMPOSITION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Luminosity
• Luminosity is a measure of the rate at which a star puts out energy.
• Larger luminosity — appears brighter
• measured in J/s or “watts”
• sometimes relative to the Sun, in “solar luminosities” L☉
• L stands for luminosity, ☉stands for Sun
• The Sun has a luminosity of 3.846×1026 W
HOW HOT IS THAT STAR?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Recall: Why Stars Shine
• Visible Sun is a hot layer of gas
• about 5800 K (5525°C, 9980°F)
• not as hot as the center!
• Glows due to hot material
• Other stars have similar structure, range of surface temperature
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Blackbody Radiation
• white light spectrum is continuous
• no gaps between colors
• the hotter you heat something, the bluer it appears
• Thermal (heat related) radiation from (relatively) hot bulk matter
• This is called blackbody radiation
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Light diagnoses Temperature
feeling warm
faint reddish glow
brighter red glow
bright orange
very bright yellow
extremely bright white
bluish whitehttp://i302.photobucket.com/albums/nn114/fiddlegirl89_photos/Dave/DSC00596-1.jpg
Colder
Warmer
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Spectrum of the Sun
• Stars emit light as blackbodies to a large extent.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Shape of Blackbody Spectrum
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Temperatue affects Color & Luminosity
• Hotter = greater luminosity
• appears brighter
• peak of curve higher
• technically greater luminosity per unit surface area
• Hotter = bluer
• peak of curve more to left
• more blue mixed in with red light
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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 Levine F2015
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
SIZE, COLOR AND TEMPERATURE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Recall
• Hotter -> Brighter
• Hotter -> Bluer
• Bigger is also brighter!
• a star with a larger diameter has a greater luminosity
http://www.skinnerscience.com/Year%2012,13/astrop3.jpg
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Analogy
• LED spotlight w/60 LEDs
• Total output ~1000 lumens
• comparable to 100-watt bulb
• each LED 1/60 of 1000 lumens
• ~16.7 lumens
• surface T gives you “per-LED” luminosity not total for star
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Stephan-Boltzman Law
is brighter than
is brighter than
is brighter than
could be brighter than
could be brighter than
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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?
A. Star A
B. Star C
C. The two stars have the same luminosity.
D. It is not possible to determine this.
Blackbody Radiation – Instructor’s Guide
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
70
2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B?
a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above.
3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible.
4) Use the graph at right to determine which of the two stars (A
or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light.
5) Use the graph at right to determine which of the two stars (A
or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this.
6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. 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 following best describes how Star A would appear as compared with Star B?
A. Star A would appear more red than Star B.
B. Both stars would appear the same color.
C. Star A would appear more blue than Star B.
Blackbody Radiation – Instructor’s Guide
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
70
2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B?
a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above.
3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible.
4) Use the graph at right to determine which of the two stars (A
or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light.
5) Use the graph at right to determine which of the two stars (A
or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this.
6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. 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 two stars (A or B) is at a higher temperature?
A. Star A is at a higher temperature than Star B.
B. Both stars have the same temperature.
C. Star B is at a higher temperature than Star A.
Blackbody Radiation – Instructor’s Guide
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
70
2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B?
a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above.
3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible.
4) Use the graph at right to determine which of the two stars (A
or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light.
5) Use the graph at right to determine which of the two stars (A
or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this.
6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. 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 two stars (A or C) is at a higher temperature?
A. Star A
B. Star C
C. The two stars have the same temperature.
D. It is not possible to determine this.
Blackbody Radiation – Instructor’s Guide
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
70
2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B?
a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above.
3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible.
4) Use the graph at right to determine which of the two stars (A
or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light.
5) Use the graph at right to determine which of the two stars (A
or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this.
6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. 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.
A. Star A is smaller than Star C.
B. Star A is larger than Star C.
C. The stars are the same size.
D. It is not possible to determine this
Blackbody Radiation – Instructor’s Guide
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
70
2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B?
a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above.
3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible.
4) Use the graph at right to determine which of the two stars (A
or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light.
5) Use the graph at right to determine which of the two stars (A
or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this.
6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. d) It is not possible to determine this.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Blackbody Radiation – Instructor’s Guide 67
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
INTRODUCTION
Prerequisite Knowledge
• Basic familiarity with the relationships between temperature, wavelength, and spectral curves
• Know that electromagnetic waves can have a large range of possible wavelengths • Know that different types of electromagnetic waves have different wavelengths • Know that visible light is a type of electromagnetic wave
Goals
• Describe an object’s appearance given its blackbody curve • Infer a star’s color and temperature from its blackbody curve • 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
TUTORIAL GUIDE 1) [ Red ]
Students have difficulty relating light curves to physical appearance and, in particular, struggle with the meaning of the word spectrum. This question introduces the concept of relative intensity.
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.
3) [ Figure a. ] 4) [ Blue and orange ]
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Spectral Classification
PRIMER ON SPECTRAL LINES
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Spectroscopy
• Spectroscope or spectrometer — astronomical instrument that breaks light into its component wavelengths
• Where light is & is not present provides information
• what an object is made of
• its physical properties
http://www.ibsen.dk/technology/images/design/modules/spectrometer-sketch.jpg
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Blackbody Spectrum
• continuous light spread across all colors
• a continuous or continuum spectrum
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Emission Spectrumn
• light is present only in selected parts of the spectrum
• emission lines
• bright bands on a black background
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Absorption Spectrum
• light is missing only in selected parts of the spectrum
• absorption lines
• dark bands on a blackbody/continuous spectrum
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Atomic Structure and Energy Levels
• Electrons in an atom (this is Hydrogen) can be modeled as being in specific “shells” or orbits around the proton.
• Each shell has a specific energy level
• Further out & higher numbered shells have a higher energy
http://odin.physastro.mnsu.edu/~eskridge/astr101/kauf5_20.JPG
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Atomic Transitions
• Electrons “prefer” to be in lower energy states
• can be kicked into a higher energy by absorbing a photon with the right energy.
• right energy , right wavelength
• E=hc/λ
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Atomic Transitions
• Electrons “prefer” to be in lower energy states
• Drops back down by spitting out a photon with the right energy
• right energy, right wavelength
• E=hc/λ
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Emission Spectrum
• This is a Hydrogen Emission spectrum
• Each line is due to a specific transition of electrons from a higher state to a lower state
• This pattern is specific to hydrogen, like a fingerprint
• 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
• Recall red stars are cooler than blue stars
• visual color isn’t very precise
• Astronomers turned to spectral properties to classify stars
• detailed classification based on line pattern
• Various schemes were tried
PICKERING’S HAREM &
THE HARVARD SPECTRAL CLASSIFICATION SCHEME
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From Cosmos
• http://www.amazon.com/gp/product/B00K0CDNOI/ref=avod_yvl_watch_now
• From “Sisters of the Sun” Episode 8
• 7:45 to ~16:00
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Harvard Computers
• The director of the Harvard Observatory from 1877 to 1919, Edward Charles Pickering hired women to process astronomical data.
• 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
• "Pickering's Harem" or “the Harvard Computers” included several now-famous astronomers
• Annie Jump Cannon,
• Henrietta Swan Leavitt
• Antonia Maury
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Modern Classification
• 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
• Cecilia Payne (Payne-Gaposchkin) discovered this was actually a temperature sequence
• More precise than BB peak or color
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Spectral Classification
• From hot to cool:
• O B A F G K M
• Each spectral class is further divided into 10 ranges
• 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
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
H-R DIAGRAM
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Spectral Class isn’t everything
• Spectral Class is not sufficient to uniquely identify a type of star
• The supergiant Arcturus and the red dwarf Proxima Centauri are both Type M & 3500 K
• They are definitely not identical!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Hertzsprung and Russell
• In 1911 Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their color
• Independently in 1913 American astronomer Henry Norris Russell plotted spectral class against absolute magnitude
• showed that the relationship between temperature and luminosity of a star was not random
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The H-R Diagram
• H-R diagram plots Color and/or Temperature against Luminosity and/or Absolute magnitude
• 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
• The long strip from upper left to lower right is called the “Main Sequence.” (MS)
• Stars spend most of their existence on the MS
• 91% of nearby stars are MS stars.
• MS stars are fusing H into He in their cores.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Giants and Dwarfs
WARM-UP QUESTION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
LECTURE-TUTORIAL ON THE H-R DIAGRAM
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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 Levine F2015
What Type of Star is Aldebaran?
A. Red Giant
B. Main Sequence
C. Supergiant
D. White dwarf
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
What Type of Star is Vega?
A. Red Giant
B. Main Sequence
C. Red Supergiant
D. White dwarf
WRAP-UP
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• Stellar Evolution
• Measuring Distances (time permitting)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Astro:8
• Astropedia:13
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• HW SS Posted, Due 11/19