1. Astronomy 1020 Stellar Astronomy Spring_2015 Day-30

2.  Sometimes you learn more from finding out that you do not understand a process.  Our first detections of neutrinos were not what were expected. PROCESS OF SCIENCE

3. Course Announcements Smartworks Chapter 14: Friday 2 Dark night observing sessions left: Mon. Apr. 13 & Thurs. Apr. 16 Reports are due Wed. Apr. 22 Exam-3: Fri. 4/10

4. Astronomy in the Fall, 2015 ASTR-1010/1011 - Planetary Astronomy + Lab (H,R) ASTR-1020/1021 - Stellar Astronomy + Lab (R) ASTR-2010 - Problems in Planet Astronomy ASTR-2011 - Intro. to Observational Astronomy ASTR-4000/4001 – Astrophotography & Lab ASTR-4170 – Special Topics in Astronomy Photometry and Filter Systems TR; 3:30-5:00pm; B310

5.  Sunspots: cooler areas in the photosphere.  Structure: dark inner umbra with surrounding penumbra.  Caused by magnetic fields.

6.  Sun shows an 11-year sunspot cycle (part of 22-year magnetic cycle).  Solar maxima: most sunspots and activity.  The Maunder Minimum showed a distinct lack of sunspots between 1645 and 1715.

7. Concept Quiz—Sunspots Sunspots have temperatures of about 4500 K. Why do sunspots appear to be dark? A.They don’t emit any light. B.They emit light, but mainly in the ultraviolet. C.They emit less energy per square meter than the photosphere (Stefan-Boltzmann). D.Light can’t pass through magnetic fields.

8.  The flux of an object is the amount of energy coming out of a square meter of surface every second.  The temperature of a sunspot on the Sun is about 1500 K less than the Sun’s surface. MATH TOOLS 14.2

9.  Solar prominences: hot rising gas in the chromosphere constrained by magnetic fields.  Solar flares and coronal mass ejections are highly energetic, violent bursts and eruptions.  Correlate with sunspot positions.

10.  Solar activity changes slightly over time.  Solar storms can disrupt electric power grids and satellites.  Cause brilliant auroras.

11.  Sun’s reach of influence on its environment is the heliosphere.  Solar wind pushes away material and helps protect Earth from harmful cosmic rays.

14. Magnetic field lines connect sunspots on the Sun’s photosphere

15. Solar magnetic fields also create other atmospheric phenomena plages filaments These features are found in the chromosphere.

16. http://www.spaceweather.com/ http://www.spaceweather.com/images2002/18mar02/cme_c3_big.gif

17. The most powerful solar flare in 14 years,... erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth. Solar Flares

18. Produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth Earth’s Magnetic Field

21. Exam - 3

23. Where do Stars Form? Spirals

24. Even in the Galactic Center

25. Where don’t Stars Form? Ellipticals

26.  The interstellar medium: gas and dust between the stars.  Near the Sun, chemical composition is similar.  Most is gas; 1 percent is interstellar dust.

27.  The gas is very tenuous: about 1 atom per cubic centimeter.  It emits various kinds of light, depending on its temperature.

28.  Dust is in the form of solid grains.  “Interstellar soot” (iron, silicon, carbon, and more).  Dust blocks visible light from stars, galaxies, etc.: interstellar extinction.

29.  Size of dust particles: large molecules up to 300 nanometers.  Therefore, dust blocks short wavelengths more efficiently.  More red light is let through: interstellar reddening.  Long wavelengths (infrared and radio) penetrate dust.

30.  A star viewed through dust is fainter and redder due to interstellar extinction and reddening.  The position of absorption lines are not affected.

31.  Dust also emits light when it blocks a star.  Energy from absorbed light is transferred to the dust, heating it.  Dust grains are typically cool (10–300 K).  Therefore, they emit infrared radiation.

32.  Most gas and dust is concentrated in relatively dense interstellar clouds.  The material found between clouds is called intercloud gas.

33.  Some regions can be very hot (10 6 K).  X-rays emitted, but extremely tenuous.  The Sun resides in a local bubble of million- degree gas.  Most intercloud gas is 8000 K.

34.  H II regions (about 10 4 K):  Hydrogen heated and ionized by ultraviolet light from hot, luminous stars (O and the hottest B).  Ionized: stripped of one or more electrons.