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Astronomy Picture of the Day: Cassini picture of Saturn, Titan and Dione

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Astronomy Picture of the Day: Cassini picture of Saturn, Titan and Dione

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  1. Explanation: A fourth moon is visible on the above image if you look hard enough. First -- and furthest in thebackground -- is Titan, the largest moon of Saturn and one of the larger moons in the Solar System. The dark feature across the top of this perpetually cloudy world is the north polar hood. The next most obvious moon is bright Dione, visible in the foreground, complete with craters and long ice cliffs. Jutting in from the left are several of Saturn's expansive rings, including Saturn's A ring featuring the dark Encke Gap. On the far right, just outside the rings, is Pandora, a moon only 80-kilometers across that helps shepherd Saturn's F ring. The fourth moon? If you look closely in the Encke Gap you'll find a spec that is actually Pan. Although one of Saturn's smallest moons at 35-kilometers across, Pan is massive enough to help keep the Encke gap relatively free of ring particles. Astronomy Picture of the Day: Cassini picture of Saturn, Titan and Dione

  2. October 26, 2011 – 10am class Section 2 Star Party: If taking the van, we’re leaving at 6:15pm sharp Section 3: Don’t forget warm clothes

  3. Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.

  4. The corona appears bright in X-ray photos in places where magnetic fields trap hot gas.

  5. How does solar activity affect humans?

  6. Coronal mass ejections send bursts of energetic charged particles out through the solar system.

  7. Solar Flare and CME as seen by the Solar Dynamic Observatory June 7, 2011

  8. Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.

  9. Solar cycle

  10. Insert TCP 6e Figure 14.21a unannotated The number of sunspots rises and falls in an 11-year cycle.

  11. The sunspot cycle has to do with winding and twisting of the Sun’s magnetic field.

  12. How does solar activity vary with time? Maunder Minimum The Little Ice Age in Europe

  13. What have we learned? • What causes solar activity? • Stretching and twisting of magnetic field lines near the Sun’s surface cause solar activity. • How does solar activity affect humans? • Bursts of charged particles from the Sun can disrupt radio communication and electrical power generation and damage satellites. • How does solar activity vary with time? • Activity rises and falls with an 11-year period.

  14. STARS What is a star? Why do they shine? How old are they?

  15. Stars shine for millions to billions of years, much longer than a human lifetime.Yet, we've been able to piece together how stars are born, shine and eventually die.

  16. The brightness of a star depends on both distance and luminosity.

  17. Properties of Stars DEFINITIONS: apparent brightness versus absolute brightness or luminosity apparent m magnitude versus absolute magnitude

  18. Inverse Square Law Same Luminosity, Twice as far away --> 4x dimmer Measure Apparent magnitude And Distance (parallax) To stars  luminosity

  19. The relationship between apparent brightness and luminosity depends on distance: Luminosity Brightness = 4 (distance)2 We can determine a star’s luminosity if we can measure its distance and apparent brightness: Luminosity = 4 (distance)2 (brightness)

  20. Thought Question How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright. B. It would be only 1/6 as bright. C. It would be only 1/9 as bright. D. It would be three times brighter.

  21. Thought Question How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright. B. It would be only 1/6 as bright. C. It would be only 1/9 as bright. D. It would be three times brighter.

  22. So how far away are these stars?

  23. p = parallax angle 1 d (in parsecs) = p (in arcseconds) 1 d (in light-years) = 3.26  p (in arcseconds) Parallax and Distance

  24. Most luminous stars: 106LSun Least luminous stars: 10–4LSun (LSun is luminosity of Sun)

  25. m M = apparent magnitude, = absolute magnitude Apparent brightness of star 1 - = m m 1 / 5 ( 100 ) 1 2 Apparent brightness of star 2 Luminosity of star 1 - = M M 1 / 5 ( 100 ) 1 2 Luminosity of star 2 The Magnitude Scale

  26. Stellar Surface Temperatures Measure the surface temperature of stars by taking a spectrum of the star and using Wien's Law.

  27. Hottest stars: 50,000 K Coolest stars: 3000 K (Sun’s surface is 5800 K.)

  28. In addition, the absorption lines in the stellar spectra are sensitive to temperature.

  29. Originally classified as A,B,C,.. the classification of stellar spectra was recast into OBAFGKM by Cecilia Payne-Gaposchkin. OBAFGKM: Oh, Be a Fine Girl Kiss Me

  30. Level of ionization also reveals a star’s temperature.

  31. Absorption lines in star’s spectrum tell us its ionization level.

  32. Lines in a star’s spectrum correspond to a spectral type that reveals its temperature. (Hottest) O B A F G K M (Coolest)

  33. Remembering Spectral Types (Hottest) O B A F G K M (Coolest) • Oh, Be A Fine Girl, Kiss Me • Only Boys Accepting Feminism Get Kissed Meaningfully

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