Foundations of Astronomy 13e Seeds Phys1411 Introductory Astronomy Instructor: Dr. Goderya Chapter 8 The Sun Star Party This Friday November 9 weather permitting. See the flyer for updates in case of cancellations due to weather conditions. See the flyer for Map details. If you attend, and signup and stay for at least 30 minutes, I will replace your lowest lab score with 100. Only if there is no cancellations. I. Introduction A. Viewing the Sun B. General Properties C. Chemical Composition D. Basic Structure II. Topics The Solar Atmosphere A. The Corona B. The Chromosphere C. Methods of Heat Transfer D. The Photosphere E. Temperature gradient in the Sun s atmosphere F. The Solar Wind Outline (continued) IV. Interior of the Sun A. Helioseismology V. The Sunspot A. Sunspots and Solar Rotation VI. Sunspot Activity A. The Solar Cycle B. Maunder Diagram C. Solar Rotation D. The Solar magnetic cycle VII. Nuclear Fusion in the Sun A. Nuclear Binding Energy B. Hydrogen Fusion C. The Solar Neutrino Problem The Sun Is Just a Normal Star A huge ball of gas on fire 1
Telescope: Visual Appearance of the Sun General Properties Limb Darkening The center of the Sun is brighter than the limb Dark Spots Average star Spectral type G2 Only appears so bright because it is so close. Absolute visual magnitude = 4.83 (magnitude if it were at a distance of 32.6 light years) 109 times Earth s diameter 333,000 times Earth s mass Consists entirely of gas (av. density = 1.4 g/cm 3 ) Central temperature = 15 million 0 K Surface temperature = 5800 0 K http://spiff.rit.edu Composition of the Sun s Gases Each element produces a specific set of absorption (and emission) lines ClassAction: Cengage Astronomy Learning 2016 Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) The Suns Atmosphere 1. The Corona 2. The Chromosphere: Plumes of fire (Spicules) The Corona Is the outermost part of the Sun s atmosphere Too thin to see visually and does Can be seen during solar eclipses or with coronagraphs The solar corona 2
The Chromosphere The Suns Surface (Photosphere) Spicules: Filaments of cooler gas from the photosphere, rising up into the chromosphere. Apparent surface layer of the sun beneath the chromosphere Depth 500 km Temperature 5800 o K Highly opaque (H - ions) Absorbs and re-emits radiation produced in the solar interior Visible in H emission. Each one lasting about 5 15 min. Three Ways of Heat Transfer The Photosphere: Granulation Is the Visible Consequence of Convection Granulation is visible as a consequence of convection The largest granules here are about the size of Texas Energy Transport in the Photosphere The Solar Atmospheric Temperature Energy generated in the sun s center must be transported outward. In the photosphere, this happens through Cool gas sinking down Convection: Bubbles of hot gas rising up Only visible during solar eclipses 1000 km Bubbles last for 10 20 min. Apparent surface of the sun Heat Flow Solar interior Temp. incr. inward 3
Why temperature in the Corona is higher than the Sun s surface? The Solar Wind A constant flow of particles from the Sun Velocity 300 800 km/s ESA ChristArt NASA Origins of Solar Wind The Solar Interior Much of the solar wind comes from coronal holes where the magnetic field does not loop back into the Sun. These open magnetic fields allow ionized gas in the corona to flow away as the solar wind. The dark area in the X-ray image at right is a coronal hole. X-Ray Images of the Sun Reveal Coronal Holes Helioseismology is a technique to measure the vibration modes in the Sun The surface of the sun moves up and down as the Sun expands and contracts. The Sun can vibrate in millions of different patterns or modes, and each mode corresponds to a different vibration wavelength Solar Winds Interact with penetrating to a different level the Earth magnetic field as seen in the figure and cause short term climate changes. The Solar Interior Doppler Mapping: Blue approaching, Red receding These oscillation can tell us about the internal structure of the Sun. Weather on The Sun The weather on the Sun is mostly magnetic caused by Sunspots. Sun Spots These are dark spots on the surface of the Sun. They are found to be highly magnetic in nature 4
Sun Spots Sunspots are Cooler Regions of the Photosphere (T 4240 K) Visible Active Regions Sunspots are cooler regions of the Photosphere (T ~ 4240K) Still brighter than the full moon when placed on the night sky Ultraviolet Observing Sunspot Sunspots do not occur at the same place on the photosphere Same group of Sunspots move with time Their motion can tell us rotation of the Sun. Differential Rotation The Sun is not a solid body as observed from sunspot rotation Maximizing Progress NASA Sunspots have Field Field Lines of a Bar Magnet North Pole South Pole Stanford Solar Center - Stanford University Loop Field Lines 5
How do We Know? Zeeman Effect Sunspot Showing Zeeman Effect In Lab. we see spectral lines split when they are in a magnetic field astronomy.swin.edu.au Lambda Scientific Systems The amount of splitting tells us what is the strength of magnetic field Sunspots field in sun spots is about 1000 times stronger than average. North Poles Prominence Emerging magnetic field lines from the Sun eject hot gas and produce Prominence loops and jets of fire South Poles In sun spots, magnetic field lines emerge out of the photosphere. Sunspot Active Regions Prominences start from one active sunspot region and end in another. The chromosphere and corona above these sunspot are violently disturbed, and are called active regions. 6
Acknowledgment The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. 7