Chapter 9 The Sun

Chapter 9 The Sun

Large Tsunami Shock Wave on the Sun

SOHO Solar and Helospheric Observatory

NSO – New Mexico

Units of Chapter 9 The Sun in Bulk The Solar Interior The Solar Atmosphere The Active Sun The Heart of the Sun

Question 1 a) core b) corona c) photosphere d) chromosphere e) convection zone The visible light we see from our Sun comes from which part? Answer: c

The Sun in Bulk

The Sun in Bulk Interior structure of the Sun Outer layers are not to scale. The core is where nuclear fusion takes place.

Question 2 The density of the Sun is most similar to that of a) a comet. b) Jupiter. c) Earth. d) interstellar gas. e) an asteroid. The density of the Sun is most similar to that of Answer: b

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 × 1026 W – the equivalent of 10 billion 1-megaton nuclear bombs per second.

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.

Question 3 The Sun is stable as a star because a) gravity balances forces from pressure. b) the rate of fusion equals the rate of fission. c) radiation and convection balance. d) mass is converted into energy. e) fusion doesn’t depend on temperature. The Sun is stable as a star because Answer: a

The Solar Interior Doppler shifts of solar spectral lines indicate a complex pattern of vibrations.

The Solar Interior Solar density and temperature, according to the standard solar model.

The Solar Interior Energy transport: The radiation zone is relatively transparent; the cooler convection zone is opaque.

The Solar Interior The visible top layer of the convection zone is granulated, with areas of upwelling material surrounded by areas of sinking material. Solar Granulation

The Solar Atmosphere Spectral analysis can tell us what elements are present, but only in the chromosphere and photosphere.

The Solar Atmosphere The cooler chromosphere is above the photosphere. Difficult to see directly, as photosphere is too bright, unless Moon covers photosphere and not chromosphere during eclipse

The Solar Atmosphere Small solar storms in chromosphere emit spicules. Solar Chromosphere

The Solar Atmosphere Solar corona can be seen during eclipse if both photosphere and chromosphere are blocked.

The Solar Atmosphere Corona is much hotter than layers below it – must have a heat source, probably electromagnetic interactions.

The Active Sun Sunspots appear dark because slightly cooler than surroundings.

The Active Sun Sunspots come and go, typically in a few days. Sunspots are linked by pairs of magnetic field lines.

The Active Sun The rotation of the Sun drags magnetic field lines around with it, causing kinks.

The Active Sun The Sun has an 11-year sunspot cycle, during which sunspot numbers rise, fall, and then rise again.

Question 7 The number of sunspots and solar activity in general peaks a) every 27 days, the apparent rotation period of the Sun’s surface. b) once a year. c) every 5½ years. d) every 11 years. e) approximately every 100 years. The number of sunspots and solar activity in general peaks Answer: d

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: few, if any, sunspots.

The Active Sun Areas around sunspots are active; large eruptions may occur in photosphere. Solar prominence is large sheet of ejected gas.

The Active Sun Solar flare is a large explosion on Sun’s surface, emitting a similar amount of energy to a prominence, but in seconds or minutes rather than days or weeks.

The Active Sun A coronal mass ejection emits charged particles that can affect the Earth.

Filament/Prominence Eruption

The Active Sun Solar wind escapes Sun mostly through coronal holes, which can be seen in X-ray images.

The Active Sun Solar corona changes along with sunspot cycle; is much larger and more irregular at sunspot peak.

Question 6 What is probably responsible for the increase in temperature of the corona far from the Sun’s surface? a) a higher rate of fusion b) the Sun’s magnetism c) higher radiation pressures d) absorption of X rays e) convection currents Answer: b

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 K.

The Heart of the Sun The process that powers most stars is a three-step fusion process.

Question 4 a) carbon (C) into oxygen (O) b) helium (He) into carbon (C) c) hydrogen (H) into helium (He) d) neon (Ne) into silicon (Si) e) oxygen (O) into iron (Fe) The proton–proton cycle involves what kind of fusion process? Answer: c

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 would give us a direct picture of what is happening in the core. Unfortunately, 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.

Question 8 a) cannot explain how the Sun is stable. b) detect only one-third the number of neutrinos expected by theory. c) cannot detect neutrinos easily. d) are unable to explain how neutrinos oscillate between other types. e) cannot create controlled fusion reactions on Earth. The solar neutrino problem refers to the fact that astronomers Answer: b

Question 5 A neutrino can escape from the solar core within minutes. How long does it take a photon to escape? a) minutes b) hours c) months d) hundreds of years e) about a million years Answer: e

Sudbury Neutrino Observatory Canada The Heart of the Sun Neutrino observatories Super Kamiokande, Japan Sudbury Neutrino Observatory Canada

Summary of Chapter 9 The Sun is held together by its own gravity and powered by nuclear fusion. Outer layers of the Sun: photosphere, chromosphere, corona. 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.

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.