Astronomy A BEGINNER’S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER The Sun Lecture Presentation © 2017 Pearson Education, Inc Chapter The Sun © 2017 Pearson Education, Inc Units of Chapter • • • • • • The Sun in Bulk The Solar Interior The Solar Atmosphere The Active Sun The Heart of the Sun Summary of Chapter © 2017 Pearson Education, Inc 9.1 The Sun in Bulk © 2017 Pearson Education, Inc 9.1 The Sun in Bulk • Interior structure of the Sun – – Outer layers are not to scale The core is where nuclear fusion takes place © 2017 Pearson Education, Inc 9.1 The Sun in Bulk • Luminosity—total energy radiated by the Sun—can be calculated from the fraction of that energy that reaches Earth • Total luminosity is about 4×0 26 W—the equivalent of 10 billion 1-megaton nuclear bombs per second © 2017 Pearson Education, Inc 9.2 The Solar Interior • Mathematical models, consistent with observation and physical principles, provide information about the Sun’s interior – In equilibrium, inward gravitational force must be balanced by outward pressure © 2017 Pearson Education, Inc 9.2 The Solar Interior • Doppler shifts of solar spectral lines indicate a complex pattern of vibrations © 2017 Pearson Education, Inc 9.2 The Solar Interior • Solar density and temperature, according to the standard solar model © 2017 Pearson Education, Inc 9.2 The Solar Interior • Energy transport: – The radiation zone is relatively transparent; the cooler convection zone is opaque © 2017 Pearson Education, Inc 9.4 The Active Sun • • Sunspots come and go, typically in a few days Sunspots are linked by pairs of magnetic field lines © 2017 Pearson Education, Inc 9.4 The Active Sun • The rotation of the Sun drags magnetic field lines around with it, causing kinks © 2017 Pearson Education, Inc 9.4 The Active Sun • The Sun has an 11-year sunspot cycle, during which sunspot numbers rise, fall, and then rise again © 2017 Pearson Education, Inc 9.4 The Active Sun • This is really a 22-year cycle because the spots switch polarities between the Northern and Southern Hemispheres every 11 years • Maunder minimum: There are few, if any, sunspots © 2017 Pearson Education, Inc 9.4 The Active Sun • • Areas around sunspots are active; large eruptions may occur in the photosphere Solar prominence is a large sheet of ejected gas © 2017 Pearson Education, Inc 9.4 The Active Sun • Solar flare is a large explosion on the Sun’s surface, emitting an amount of energy similar to a prominence, but in seconds or minutes rather than days or weeks © 2017 Pearson Education, Inc 9.4 The Active Sun • A coronal mass ejection emits charged particles that can affect Earth © 2017 Pearson Education, Inc 9.4 The Active Sun • Solar wind escapes the Sun mostly through coronal holes, which can be seen in X-ray images The coronal hole is the dark V-shaped region © 2017 Pearson Education, Inc 9.4 The Active Sun • Solar corona changes along with the sunspot cycle It is much larger and more irregular at sunspot peak © 2017 Pearson Education, Inc 9.5 The Heart of the Sun • Nuclear fusion requires that like-charged nuclei get close enough to each other to fuse • This can happen only if the temperature is extremely high—over 10 million kelvins © 2017 Pearson Education, Inc 9.5 The Heart of the Sun • The process that powers most stars is a three-step fusion process, the proton–proton chain © 2017 Pearson Education, Inc 9.5 The Heart of the Sun • Neutrinos are emitted directly from the core of the Sun and escape, interacting with virtually nothing Being able to observe these neutrinos gives us a direct picture of what is happening in the core • They are no more likely to interact with Earth-based detectors than they are with the Sun; the only way to spot them is to have a huge detector volume and to be able to observe single interaction events © 2017 Pearson Education, Inc 9.5 The Heart of the Sun • Neutrino observatories © 2017 Pearson Education, Inc Summary of Chapter • • • • • The Sun is held together by its own gravity and powered by nuclear fusion Outer layers of the Sun are the photosphere, chromosphere, and corona The photosphere is the visible “surface” of the Sun The corona is very hot Mathematical models and helioseismology give us a picture of the interior of the Sun Sunspots occur in regions of high magnetic fields; darker spots are cooler © 2017 Pearson Education, Inc Summary of Chapter 9, cont • • Nuclear fusion converts hydrogen to helium, releasing energy Solar neutrinos come directly from the solar core, although observations have told us more about neutrinos than about the Sun © 2017 Pearson Education, Inc .. .Chapter The Sun © 2017 Pearson Education, Inc Units of Chapter • • • • • • The Sun in Bulk The Solar Interior The Solar Atmosphere The Active Sun The Heart of the Sun Summary of Chapter. .. fusion takes place © 2017 Pearson Education, Inc 9.1 The Sun in Bulk • Luminosity—total energy radiated by the Sun—can be calculated from the fraction of that energy that reaches Earth • Total luminosity... 2017 Pearson Education, Inc 9.4 The Active Sun • A coronal mass ejection emits charged particles that can affect Earth © 2017 Pearson Education, Inc 9.4 The Active Sun • Solar wind escapes the