Astronomy 1020 Stellar Astronomy Spring_2016 Day-27

Course Announcements Apr. 1 – (FRIDAY) Last day to drop a class with W, F, FA Remaining Observing nights: Dark – Thurs. 3/31, the observatory Dark – Tues. 4/5, the observatory 1 st Q – Wed. 4/13, 7:30pm on campus Observing Reports are due: Mon. 4/18 at class time. Exam-3 target, Monday 4/4 (Ch. 13, 14 (& 15 ?) SW Ch. 13, 14, (& 15 ?) due Monday 4/4

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

 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.

Magnetic field lines connect sunspots on the Sun’s photosphere

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

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

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

Where do Stars Form? Spirals

Where don’t Stars Form? Ellipticals

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

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

 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.

 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.

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

 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.

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

 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.

 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.

 At lower temperatures, hydrogen is in single, neutral atoms.  This gas emits radio waves with = 21 cm.  Light of this wavelength penetrates the dust.  Good for mapping the Milky Way.