ASTR 1120 General Astronomy: The SUN � ast Tim � Stars & Galaxies How far is the Sun? � NNOUNCEMENTS What is the Sun made of? FIRST MIDTERM THIS THURSDAY, 09/17 How does the Sun produce its energy? � ex � observing night Tue 09/22. (and how do we know?) Why is the Sun stable? � econd homework on mas � ring as � onomy due o � � UESDAY, 09/22, by 5pm. What is the structure of the Sun? Clicker Question Clicker Question In the core, what is the main wavelength In the core, what is the main wavelength of photons present? of photons present? A. Radio waves A. Radio waves B. Gamma Rays B. Gamma Rays C. Visible C. Visible D. Infrared D. Infrared E. X-rays E. X-rays
Clicker Question Clicker Question At the photosphere, what is the main At the photosphere, what is the main wavelength of photons present? wavelength of photons present? A. Radio waves A. Radio waves B. Gamma Rays B. Gamma Rays C. Visible C. Visible D. Infrared D. Infrared E. X-rays E. X-rays How do we know what’s inside the Sun? Helioseismology: Millions of sound SOLAR OSCILLATION waves available to probe solar interior MODES Some waves bounce just below the surface Others almost make it to the center All excited by turbulent One of millions of modes, each granulation visible in with a different photosphere tone! ACOUSTIC WAVES
Sunspots Sunspots Caused By Magnetic Fields • Darker = cooler – Still ~4,000 K • Sunspot pictured at the bottom left covers the area of 15 Earths! – Taken with the Solar and Heliospheric Observatory (SOHO) • Magnetic fields entrain gas in huge bubbling loops • Cooler areas at “liftoff” cause dark sunspots But What Causes the Magnetic This Solar “Wind Up” Leads Field Lines to Stick Out Like That? To The Sunspot Cycle • Differential Rotation – The Sun rotates differently at different latitudes. • The Sun winds itself up
Complex Interplay of Convection, Magnetism and During the Sunspot Cycle Sunspots Differential Rotation. Form At Different Latitudes Clicker Question Clicker Question What is believed to be the main cause of the What is believed to be the main cause of the sunspot cycle? sunspot cycle? A. Temperature changes between the equator and A. Temperature changes between the equator and poles of the Sun poles of the Sun B. Twisting of magnetic fields lines in the Sun due to a B. Twisting of magnetic fields lines in the Sun due to a rotation rate varying with latitude. rotation rate varying with latitude. C. Variability in the Sun’s brightness every 11 years C. Variability in the Sun’s brightness every 11 years D. Interaction between the Sun and the orbits of the D. Interaction between the Sun and the orbits of the innermost planets innermost planets E. A variation of the fusion rate occurring in the core of E. A variation of the fusion rate occurring in the core of the Sun. the Sun.
If we see the sunspot edge-on, it’s called a PROMINENCE Coronal MASS Ejections Blast When Prominences Go Bad Out Charged Particles • Occasionally the magnetic field lines • PROTONS! in a prominence – Can: “snap” • Damage satellites – Energy & Light is • Harm astronauts released • Induce currents on Earth and destroy electric • Flares transformers on the ground – Charged particles • Cause swelling in the Earth’s atmosphere are spewed out into space • Coronal Mass Ejections
Protons interacting with the Earth’s magnetic field produce aurora Coronal Mass Ejections Movie from Solar and Heliospheric Observatory http://sohowww.nascom.nasa.gov/ Outside the chromospere, the Chromosphere temperature spikes up again! • Temperature goes back UP! • T � 6,000-10,000 K • Very thin density • Heated by energy twisting and spilling around magnetic field lines
Corona X-ray image of the Sun • T � 1,000,000 K • Extremely thin density • X-rays • More magnetic heating Solar Eclipse: Sun’s light Solar Wind blocked by the Moon • At the top of the corona, gas is hot enough (and far enough) to escape the gravity of the Sun • In effect, the corona is “evaporating” – But replenished from below • Solar wind carries about a million tons of solar matter per second!! Corona becomes clearer in visible light without glare from the – Yet the sun has only lost 0.1 percent of its mass! rest of the Sun
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