Chapter 10: Measuring Stars Planetarium Extra Credit Opportunity! - - PowerPoint PPT Presentation

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Chapter 10: Measuring Stars Planetarium Extra Credit Opportunity! - - PowerPoint PPT Presentation

Feb 29, 2024 326 likes •734 views

Chapter 10: Measuring Stars Planetarium Extra Credit Opportunity! Chapter 10 Reading Assignment due today at (see the syllabus) 10:45am Sept. 26th or 28th at 6:45 pm for Chapter 11 Reading Assignment due Tuesday, the Night Vision show

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Chapter 10: Measuring Stars

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Chapter 10 Reading Assignment due today at 10:45am Chapter 11 Reading Assignment due Tuesday, October 1st Are your grades in Canvas correct??? Planetarium Extra Credit Opportunity! (see the syllabus)

  • Sept. 26th or 28th at 6:45 pm for

the “Night Vision” show at the Clark Planetarium Free tickets available from me, $2 otherwise

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

What’s easy to measure for stars?

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  • Their positions on the celestial sphere
  • Their spectra (brightness as a function of wavelength)
  • ~Changes in position and spectrum~
  • Their distance
  • Their size (resolving them)
  • Their mass

What’s hard to measure for stars?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

How do we measure distances on the Earth?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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1) Calibration: hold your pinky finger at arm’s length, close one eye, and measure its width (this is about 1 degree in angle) 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Example: Cuzco is about 1.5 units long

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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2) Close your left eye and center a finger or pen on the “1” line 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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3) Open your left eye, close your right eye, and measure how far your finger moved 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Example: Cuzco appeared to move 9.25 units

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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4) Divide the apparent movement by the width of your pinky to get the angle in degrees 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Example: 9.25 / 1.5 = 6.2 degrees

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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5) Divide 110 inches by the number of degrees to get the distance to your finger! 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Example: 110 inches / 6.2 degrees ~ 18 inches

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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5) Divide 110 inches by the number of degrees to get the distance to your finger! 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 2.5in

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Parallax

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Place your finger about 1 foot away and repeat the test. What distance did you get? 1 unit 1/2 unit 1/4 unit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 2.5in

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10 11

Parallax

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 12

Which star is the most luminous?

A B C

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Distance and Brightness gives Luminosity

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Star’s Brightness Star’s Luminosity 4 π distance2

=

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 14

A B Which case for the red star would have the larger parallax?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

What’s easy to measure for stars?

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  • Their positions on the celestial sphere
  • Their spectra (brightness as a function of wavelength)
  • ~Changes in position and spectrum~
  • Their distance
  • Their size (resolving them)
  • Their mass

What’s hard to measure for stars?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Emission and Absorption Lines

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Emission sticks up Absorption sticks down Electron Nucleus

Higher energy electron = Further from nucleus

Change in electron’s energy = Energy of Emitted Light

Electrons and Emission

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Each atom has a unique set of energy levels

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Remember: Light is “Quantized”

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Spectra Lab: Emission Tubes

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Spectra Lab: Emission Tubes

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Spectra Lab: Blackbody Emission

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 22

If you see a star bluer than the sun, would you expect it to have a lower or higher luminosity? If a star is very faint, what color would you expect it to be?

In small groups, discuss this question and your reasoning:

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Spectra Lab: Blackbody Emission

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10 24

Typical stellar spectrum has many absorption lines, which we graph

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Chapter 10: Measuring Stars

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Chapter 11 Reading Assignment due Tuesday, October 1st Are your grades in Canvas correct??? Planetarium Extra Credit Opportunity! (see the syllabus)

  • Sept. 26th or 28th at 6:45 pm for

the “Night Vision” show at the Clark Planetarium Free tickets available from me, $2 otherwise

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 26

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

What kind of spectrum does the Moon have?

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A) Emission Line B) Blackbody C) Absorption Line

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Annie Jump Cannon Classifies the Stars

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  • one of “Pickering’s Women,” a

Harvard “Calculator”

  • part of the effort to catalog every star

in the sky down to 9th magnitude

  • defined the classification scheme for

stellar spectra

  • manually classified over 350,000

stars

  • realized stellar types correlated with

temperature (but not in the original

  • rder)
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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 29

Balmer series (n=x -> n=2)

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 30

Balmer series (n=2 -> n=x)

Small Numbers

  • f Atoms in E2

Large Numbers

  • f Atoms in E2

More Violet Light More Red Light

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

If temperature is what we want, why use spectra?

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Dust preferentially absorbs bluer light (uniformly), so a star’s color will change (but the relative strengths of its lines will not)

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Color and temperature are connected

32 1 μm = 1000 nm

Temperature [in K]

Wien's Law:

λmax = 2900 μm⋅K

Stefan-Boltzmann Law: Luminosity per unit area = constant × Temperature4

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Binary Stars

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Weighing stars in a Binary

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

What’s easy to measure for stars?

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  • Their positions on the celestial sphere
  • Their spectra (brightness as a function of wavelength)
  • ~Changes in position and spectrum~
  • Their distance
  • Their size (resolving them)
  • Their mass

What’s hard to measure for stars?

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Hertzsprung-Russell (HR) Diagram

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Spectral Type, Color, Temperature

  • n the x-axis

Luminosity (intrinsic brightness)

  • n the y-axis
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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Globular Cluster Color-Magnitude Diagram

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Bluer Redder Fainter Brighter

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10

Gaia CMDs

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66 million stars

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ASTR/PHYS 1060: The Universe Fall 2019: Chapter 10 39

Hydrogen-burning stars fall on the Main Sequence in a specific place determined by their mass

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Fall 2019: Chapter 10 ASTR/PHYS 1060: The Universe 40

Star P: Spectral Type: B5 Luminosity: 300 Lsun Star Q: Spectral Type: K3 Luminosity: 0.008 Lsun 100 1000 P Q 0.01 0.001