1 / 37

Starlight and What it Tells Us

Starlight and What it Tells Us. The Stars in the Sky. Vary in Brightness Distance Size Vary in Color Color = Temperature. Star Names. Proper star names mostly Arabic Greek Letters, Numbers Catalog Identifiers Faint stars usually have no name. The Names of Sirius.

alika
Download Presentation

Starlight and What it Tells Us

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Starlight and What it Tells Us

  2. The Stars in the Sky Vary in Brightness • Distance • Size Vary in Color • Color = Temperature

  3. Star Names • Proper star names mostly Arabic • Greek Letters, Numbers • Catalog Identifiers • Faint stars usually have no name

  4. The Names of Sirius • Alpha Canis Majoris (Bayer, 1603) • 9 Canis Majoris (Flamsteed, 1725) • BD -16 1591 (Bonner Durchmusterung 1859-1903) • HR 2491 (Harvard Revised Catalog, 1908) • HD 48915 (Henry Draper, 1918-1924) • ADS 5423 (Aitken Double Star Catalog, 1932) • HIP 32349 (HIPPARCOS, 1997)

  5. The Heavens Are Not Changeless • The Stars Move • Most of our constellations would have been unrecognizable to Neanderthal Man • The Solar System Moves • Very few of our nearby stars would have been visible to the first humans • Stars are Born, Live and Die • Many of our brightest stars did not exist in the days of the dinosaurs

  6. Brightness of Stars • Variations in distance and intrinsic brightness • Scale based on one by Hipparcos 500 B.C. • Magnitude: Large Numbers = Fainter • One magnitude = 2.5 x • Five magnitudes = 100 x

  7. Magnitudes • Planet around nearby star: 30 • Pluto: 13 • Faintest Naked-Eye Star: 6 • Big Dipper Stars: 2 • Sirius (Brightest Star) -1.6 • Venus -4 • Full Moon -12 • Sun -27

  8. Absolute Magnitude • Altair and Deneb are about equally bright as seen from Earth • Altair is 16 l.y. away, Deneb 1600 • Hence Deneb must be about 10,000 times brighter

  9. Absolute Magnitude • How bright a star would be at a distance of 32.6 l.y. (10 parsecs) • Sun: 4.5 (inconspicuous naked-eye star) • Altair: 2.2 • Deneb: -7.1 (bright as crescent moon) • Note: Deneb - Altair about 10 magnitudes = 100 x 100 = 10,000 times

  10. Black-Body Radiation • Objects Emit Radiation Because They Are Hot • Why “Black”? Because None of the Radiation is Reflected from Some Other Source • The Sun Emits Black-Body Radiation, Mars Does Not • Close Example of pure Black-Body radiation: Peephole in a pottery kiln

  11. Black Body Radiation

  12. What’s The Source of the Light?

  13. Color = Temperature

  14. Why Black-Body Radiation is so Important • Color is directly related to temperature • Temperature is the only determinant of color • Energy per unit area is the same if temperature is the same • If two stars have the same color and distance, difference in brightness is due to difference in size • Dwarf and giant stars are literally dwarfs or giants

  15. Sirius and the Pup

  16. Sirius and the Pup • Sirius M = -1.5; Pup M = 8.5 • 10 magnitude difference • 100 x 100 = 10,000 times brightness distance • Sirius and the Pup are same color, therefore same temperature (Pup is hotter) • Pup must have 1/10,000 the apparent area of Sirius = 1/100 the diameter

  17. Spectroscopy • Different atoms absorb or emit specific wavelengths of light • When light spread into a spectrum, the absorbed wavelengths show up as dark (missing) bands • These spectral lines are indicators of: • Chemical composition • Physical conditions

  18. Atoms and Radiation

  19. The Solar Spectrum

  20. Spectra and Spectral Lines • Continuous Spectrum: Incandescent solids or liquids (steel mill) and dense hot gases (Sun’s photosphere) • Emission Spectrum: Thin hot gases (fireworks, sodium or mercury vapor lights, Sun’s chromosphere • Absorption Spectrum: Light shining through thin gases (Sun and star light)

  21. How the Chromosphere Works

  22. Spectral Lines are Affected By: • Electrical and Magnetic Fields • Number of Electrons Atoms Have Lost (Indicates Temperature and Pressure) • Motion (Doppler Effect) • Blue-shifted if Motion Toward Observer • Red-shifted if Motion Away From Observer

  23. The Doppler Effect

  24. What the Doppler Effect Tells Us • Radial Motion • Rotation of Stars • Approaching side of star blue-shifted, receding side red-shifted • Unseen Companions (Stars or Planets) • Star oscillates around center of mass • Surface and Interior Motions • Changes in Size • Interior Oscillations

  25. Spectral Classification of Stars • W – very hot young stars expelling their outer layers • Main Sequence: O, B, A, F, G, K, M (hottest to coolest) • “Oh be a fine girl/guy, kiss me” • Subdwarfs: L, T, Y (hottest to coolest) • Chemically Peculiar Stars: C, N, R, S • White Dwarfs: D

  26. Spectral Signatures of Stars • O: Ionized Helium • B: Neutral Helium • A: Strongest Hydrogen Lines • F: Ionized Calcium • G: Strongest Calcium Lines + Neutral Metals • K: Neutral Metals Dominate • M: Titanium Oxide

  27. The Hertzsprung-Russell Diagram

  28. The Main Sequence: O • 30,000-60,000 K (Blue-white) • Absolute Magnitude -5 • 1,000,000 times Sun’s Luminosity • 16 times Sun’s Diameter • 64 times Sun’s Mass • Lifetime: Less than a million years • Examples: Orion's Belt

  29. The Main Sequence: B • 10,000-30,000 K (Blue-white) • Absolute Magnitude -3 • 20,000 times Sun’s Luminosity • 7 times Sun’s Diameter • 18 times Sun’s Mass • Lifetime: 10 million years • Examples: Spica

  30. The Main Sequence: A • Temperature: 7500-10,000 K (White) • Absolute Magnitude +0.5 • 40 times Sun’s Luminosity • 2 times Sun’s Diameter • 3 times Sun’s Mass • Lifetime: 600 million years • Examples: Vega, Sirius

  31. The Main Sequence: F • Temperature: 6000-7500 K (Yellow-White) • Absolute Magnitude +2.5 • 6 times Sun’s Luminosity • 1.5 times Sun’s Diameter • 1.7 times Sun’s Mass • Lifetime: 2.5 billion years • Examples: Procyon

  32. The Main Sequence: G • Temperature: 5000-6000 K (Yellow) • Absolute Magnitude +5 • 1 times Sun’s Luminosity • 1 times Sun’s Diameter • 1 times Sun’s Mass • Lifetime: 10 billion years • Examples: Sun, Alpha Centauri A

  33. The Main Sequence: K • Temperature: 3500-5000 K (Orange) • Absolute Magnitude +6 • 0.4 times Sun’s Luminosity • 0.9 times Sun’s Diameter • 0.8 times Sun’s Mass • Lifetime: 10 billion years • Examples: Alpha Centauri B

  34. The Main Sequence: M • Temperature: 2000-3500 K(Red) • Absolute Magnitude +10 to +15 • 0.04 times Sun’s Luminosity • 0.5 times Sun’s Diameter • 0.4 times Sun’s Mass • Lifetime: 5 trillion years • 75% + of all stars • Examples: Barnard's Star, Proxima Centauri

  35. Sub-Dwarfs • L: 1300-2000 K, Borderline stars with alkali metals and metal hydrides • T: 700-1300 K, Substellar, methane in spectra • Y <700 K, Substellar, ammonia in spectra (predicted)

More Related