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ASTR 1040

ASTR 1040. First Homework Due Today Next Observatory opportunity 9/26 Planetarium on 9/26 First Exam October 5. Website http://casa.colorado.edu/~wcash/APS1040/APS1040.html. Fusion vs. Fission. Fusion: Atoms unite and release energy (Fuse) New atom must be no heavier than iron z=26.

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ASTR 1040

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  1. ASTR 1040 First Homework Due Today Next Observatory opportunity 9/26 Planetarium on 9/26 First Exam October 5 Website http://casa.colorado.edu/~wcash/APS1040/APS1040.html

  2. Fusion vs. Fission Fusion: Atoms unite and release energy (Fuse) New atom must be no heavier than iron z=26 Fission: Heavy atoms split to release energy Initial atom must be heavier than iron WWII Nukes were fission bombs made of U and Pu Sun works on FUSION of H into He

  3. Proton-Proton Chain Bottom Line: H+H+H+H  He 1H1 +1H1 1H2 + e+ + n 1H2 +1H1 2He3 + g 2He3 +2He3 2He4 + 1H1+ 1H1 5x106 < T < 2x107K

  4. CNO Cycle 6C12 +1H1 7N13 + g 7N13 6C13 + e+ + n 6C13 +1H1 7N14 + g 7N14 +1H1 8O15 + g 8O15 7N15 + e+ + n 2x107 < T < 108K 7N15 +1H1 6C12 + 2He4 Net: 1H1 +1H1 + 1H1 +1H1 2He4 + 2e+ + 4g +2n hydrogen -> helium + energy

  5. Triple-a Reaction 2He4 +2He4 4Be8 + g T > 108K 4Be8 +2He4 6C12 + g Must be very dense for this to work Be8 decays back into helium very quickly unless struck by another He4 Too low density in Big Bang Net: 2He4 +2He4 + 2He4 +2He4 6C12 + 2g helium -> carbon + energy

  6. Solar Schematic

  7. Sunspots Seen by Ancient Persians

  8. Groups of Sunspots

  9. Solar Corona Visible in Eclipse

  10. The 1999 Eclipse

  11. August 21, 2017

  12. The Sun Viewed in X-rays

  13. X-ray Movie

  14. X-ray Loops

  15. Magnetic Structure

  16. Dynamic Structure

  17. Solar Turbulence

  18. Differential Rotation Rotates in 25 days at Equator 28 days Mid Latitude 30 days Poles Rapidly Twists Up

  19. Pressure Balance • P=1.5nkT • n is particles per cm3 • k = 1.4x10-16 in cgs units (Boltzman’s Constant) • T is temperature in Kelvins • P=B2/8 • B is magnetic field in Gauss P is pressure in ergs/cm3 = dynes/cm2

  20. Example • B= 0.3G (about Earth) • PB = 0.32 / 8 /3.14 = 3.5x10-3 erg/cm3 • Patmosphere = 1.5nkT = 1.5x2.5x1019x1.4x10-16x300 = 1.5x106 erg/cm3 • That’s why the weather report never includes the magnetic activity of the Earth

  21. Sunspots Erupt in Groups

  22. Sunspot Cycle During mid 1600’s sunspots became non-existent Maunder Minimum

  23. Solar Wind 5x105K Corona 2x106K Transition Region 105K Chromosphere 104K Photosphere 5500K

  24. Solar Wind Passes Earth

  25. Summary: Sun as a Star • Formed from cloud 4.6x109 years ago • Collapsed to present size • stabilized by nuclear reactions • Emits 4x1026 W • Runs on proton-proton chain and CNO cycle • Now 20% brighter • Turbulent upper envelope • Magnetic Fields from Differential Rotation • Sunspots, Corona, Solar Wind • Activity Cycle 11 years

  26. STARS

  27. Stars are grouped in Galaxies • Sun and all the stars we see are part of Milky Way Galaxy • We all orbit a common center • Sun is 3x1020m from center of MW You are here Each star orbits center Disk Stability Again

  28. Distances to the Stars • Closest Star, Proxima Centauri is 4x1016m away. (Alpha Cen ~4.3x1016m) • Need a more convenient unit

  29. The Light Year Light Travels at 300,000km/s (186,000miles/s = 3x108m/s) That’s one foot per nanosecond One Year is 3.15x107 seconds long In one year light travels 3.15x107x3x108 = 1016m This is the definition of a light year. Prox Cen is at 4ly.

  30. Question • There’s a big black hole in the Center of the Milky Way at a distance of 3x1020m. How long does it take for its light to reach us? • A) 3years • B) 30 years • C) 300 years • D) 3000 years • E) 30,000 years

  31. Question • There’s a big black hole in the Center of the Milky Way at a distance of 3x1020m. How long does it take for its light to reach us? • A) 3years • B) 30 years • C) 300 years • D) 3000 years • E) 30,000 years

  32. The Parsec Astronomers use the parsec as a measure of distance 1pc = 3ly 1pc = 3x1016m Origin of parsec comes from method of measuring distance

  33. Each Star Orbits the Center

  34. How Long does that Take? Takes about a hundred million years to circumnavigate the galaxy

  35. Star Names • Arabic Names • Antares, Capella, Mira, etc. • Constellations a Orionis, b Cygni, … then 49 Ori, 50 Ori, etc. • Catalogues HD80591, SAO 733421, etc • RA and Dec – just position in the sky

  36. Proper Motion 2003 All stars move Nearby stars move faster Appear to move against fixed field Can Take Many Years Use Old Photographic Plates 1900

  37. Parallax I year cycle

  38. The Parsec 1 parsec 1AU 1 arcsecond 360 degrees in circle 60 arcminutes per degree 60 arcseconds per arcminute 200,000AU = 1 parsec = 3x1016m parsec ---- parallax second

  39. Question • Based on the definition of a parsec , if star A has a parallax of 0.5 arcseconds and star B has a parallax of 0.75 arcseconds which one is farther from the Earth? • A. Star B is farther away because it has a higher parallax • B. Star A is farther away because it has a lower parallax • C. All stars are the same distance away from the Earth • D. It is impossible to tell from this information.

  40. Question • Based on the definition of a parsec , if star A has a parallax of 0.5 arcseconds and star B has a parallax of 0.75 arcseconds which one is farther from the Earth? • A. Star B is farther away because it has a higher parallax • B.Star A is farther away because it has a lower parallax • C. All stars are the same distance away from the Earth • D. It is impossible to tell from this information.

  41. Measure Parallax distance to a star in parsecs = 1/(parallax in arcseconds) e.g. measure .04” parallax, then distance is 25pc Measuring Parallax was first successful way to measure distances to stars after centuries of trying Took high speed photography in 1890’s to do it.

  42. Question • The parallax of an observed star is 0.1 arcseconds, how many lightyears is it away from Earth? • a. 1 light year • b. 3 light years • c. 10 light years • d. 30 light years • e. 75 light years

  43. Question • The parallax of an observed star is 0.1 arcseconds, how many light years is it away from Earth? • a. 1 light year • b. 3 light years • c. 10 light years • d. 30 light years (10parsecs) • e. 75 light years

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