Chapter 15 The Sun

Solar Prominence – photo by SOHO spacecraft from the Astronomy Picture of the Day site link

SOHO (before launch, at ESA facility) (without solar panels) Gallery of the SOHO spacecraft: http://sohowww.nascom.nasa.gov/gallery/Spacecraft/ SOHO spots 2000th comet http://sohowww.nascom.nasa.gov/hotshots/2010_12_28/

Solar and Heliospheric Observatory (SOHO) (link) is in orbit around the sun near the L1 point

STEREO mission – two spacecraft on opposite sides of the Sun Each is in an orbit similar to Earth’s orbit, but one moves ahead of Earth, and the other trails behind Earth. The separation has been increasing over time. The purpose is to continuously monitor the entire surface of the Sun, to help predict space weather (solar winds). http://www.nasa.gov/mission_pages/stereo/main/index.html

SOHO: Ultraviolet pictures of the Sun

The closest star - The Sun

The Sun is a layered structure

The atmosphere of the Sun The outer layers are all parts of the Sun’s atmosphere: Corona Transition zone Chromosphere The Photosphere is the “surface” of the Sun; it emits the light that we see. The Convection and Radiation Zones are named for how energy is transported in the interior of the Sun.

Solar Granulation in the photosphere can be seen in movies taken by the SOHO cameras This granulation shows that convection is occurring under the surface of the Sun. On average these granules are about the size of a large state like Texas (up to 1000 miles across).

Above the granular photosphere is the chromosphere.

Solar spicules are relatively cool and hence dark features that appear above the chromosphere. These spicules are jets of gas that rise up above the chromosphere.

Absorption of various wavelength of light occurs in the solar chromosphere This region is usually only visible to us during a total solar eclipse. Also visible in this photo are prominences.

Next are the transition zone and the Solar Corona

The Solar Corona is most obvious during a total solar eclipse.

Coronal Hole, seen in X-ray images by Yohkoh.

Solar Atmospheric Temperature So much energy is flowing through this region and the density is so low that the temperature of these regions is very high. All of this energy causes gas to “boil” off into space, or causes gas to be “pushed” off the surface of the Sun. This gas is called the Solar Wind.

Solar Spectrum in the visible region

Solar Spectrum This absorption spectra tells us what elements are in the Sun’s chromosphere and most likely in the rest of the Sun, except in the core.

Sunspots Sunspots are cooler regions of the Sun’s surface

Sunspots are also regions of intense magnetic fields. Sunspots, Up Close Sunspots are also regions of intense magnetic fields. Just like regular magnets, sunspots come in pairs one is a “North pole” and one is a “South pole” Dark region – umbra (4300 K) Brighter region – penumbra (5000 K) Granules – (5800 K)

Sunspot Magnetism

Sunspots behave somewhat like a horseshoe magnet, causing a magnetic field above the photosphere.

Above the sunspot, the magnet field causes the hot gas of the corona to concentrate along the field lines, seen here is a photo in the ultraviolet.

See next slide for detail

Solar Rotation The Sun has Differential rotation which means different parts of the Sun rotate at different speeds. The Sun’s equator rotates faster than at the poles.

Solar Rotation “drags” the magnetic field around. All of the sunspot pairs in the north hemisphere have the same polarity or orientation. All of the sunspot pairs in the southern hemisphere have the opposite polarity.

Sunspot Cycle Both the number and the location of the sunspots change during the Sunspot or Solar Cycle which lasts 11 years

Maunder Minimum The solar cycle has varied a lot in the past and we still do not know all of the details of how it works.

An active corona occurs at the peak of the sunspot cycle.

Many Prominences, Flares, and Coronal Mass Ejections can be seen. The “active Sun” refers to times when there are lots of sunspots and the surface of the Sun is very active in other ways. Many Prominences, Flares, and Coronal Mass Ejections can be seen. Also during this time the corona becomes larger and more irregularly shaped. This year, 2018, we are in a period of solar minimum. See https://www.youtube.com/watch?v=kBKJkU06ICQ

Solar Prominences are huge outbursts of hot gases that blow out into space, then often the gas cools and falls back into the Sun.

are loops of hot gas that rise from the surface of the sun. They are Solar Prominences Solar Prominences are loops of hot gas that rise from the surface of the sun. They are shaped by the magnetic fields of the Sun. SOHO website: http://sohowww.nascom.nasa.gov/ For Mar. 28, 2014, there is a movie of 8 CMEs in five days: https://sohowww.nascom.nasa.gov/pickoftheweek/old/28mar2014/

Solar Flares are much more rapid than prominences.

Solar Flare A rapidly expanding "solar quake" on the Sun’s surface depicted here by the Michelson Doppler Imager (MDI). It immediately followed a solar flare on 1996 July 6 and spread out more than 100,000 km at the solar surface. Scientists have shown that solar flares produce seismic waves, and gigantic seismic quakes, in the Sun's interior. They have tracked these seismic waves and found that "sun-quakes" closely resemble earthquakes on our planet. http://sohowww.nascom.nasa.gov/

A Solar flare on Nov. 11, 2003. SOHO obtained numerous images of the active Sun in fall 2003.

Coronal Mass Ejection Coronal Mass Ejection events (CME) is when an eruption on the surface of the Sun ejects large amounts of gas into space. These events are larger than solar flares and are less frequent.

Coronal Mass Ejections throw huge amounts of material into space, which can have effects on Earth if it hits us.

Coronal Mass Ejection (we’ll show movies) Also see www. spaceweather Coronal Mass Ejection (we’ll show movies) Also see www.spaceweather.com for recent news. http://sohowww.nascom.nasa.gov/

Solar Oscillations can be used to understand the interior of the sun in a way similar to seismological studies of the Earth; this is called Helioseismology. (link to GONG)

Helioseismology has been especially useful in understanding the region just under the photosphere. The core of the Sun has been modelled using theoretical physics calculations and data from nuclear experiments.

FIGURE 10-21 The Solar Model (a) Thermonuclear reactions occur in the Sun’s core, which extends to a distance of 0.25 solar radius from the center. In this model, energy from the core radiates outward to a distance of 0.8 solar radius. Convection is responsible for energy transport in the Sun’s outer layers. (b) The Sun’s internal structure is displayed here with graphs that show how the luminosity, mass, temperature, and density vary with the distance from the Sun’s center. A solar radius (the distance from the Sun’s center to the photosphere) equals 696,000 km. (c) Ten most common elements in the Sun, by the numbers of atoms of each and by the percentage of the Sun’s total mass they each comprise. (a: NASA)

ionized but the protons do not have enough velocity to hit each other Nuclear fusion reactions occur at high temperature in the core, which causes particles to slam into each other at high speed. At lower temperatures, hydrogen atoms are ionized but the protons do not have enough velocity to hit each other because of electric force. At higher temperatures, the protons have more velocity, so when they hit each other they can fuse together to form a nucleus of deuterium (and a positron and a neutrino).

Solar Fusion occurs in several reaction stages, all occurring simultaneously in the core of the Sun.

See details on following slides

Radiant energy from the core travels quickly outward through the radiation zone to heat the convection zone.

FIGURE 10-21 The Solar Model (a) Thermonuclear reactions occur in the Sun’s core, which extends to a distance of 0.25 solar radius from the center. In this model, energy from the core radiates outward to a distance of 0.8 solar radius. Convection is responsible for energy transport in the Sun’s outer layers. (b) The Sun’s internal structure is displayed here with graphs that show how the luminosity, mass, temperature, and density vary with the distance from the Sun’s center. A solar radius (the distance from the Sun’s center to the photosphere) equals 696,000 km. (c) Ten most common elements in the Sun, by the numbers of atoms of each and by the percentage of the Sun’s total mass they each comprise. (a: NASA)

This neutrino detector near Kamioka, Japan, is called the Super-KamiokaNDE. (Kamioka Neutrino Detection Experiment) (Workers are seen inspecting the phototubes, with some of the water drained out of the large tank, which is deep underground.) This detects neutrinos from the core of the Sun.

A Solar Neutrino Experiment in the Sudbury Neutrino Observatory, in an old nickel mine near Sudbury, Canada. This and other experiments confirm the Solar Model described on the previous slides. FIGURE 10-22 The Solar Neutrino Experiment Located 6800 feet underground in the Creighton nickel mine in Sudbury, Canada, the Sudbury Neutrino Observatory is centered around a tank that contains 1000 tons of water. Occasionally, a neutrino entering the tank interacts with one or another of the particles already there. Such interactions create flashes of light, called Cerenkov radiation. Some 9600 light detectors sense this light. The numerous silver protrusions are the back sides of the light detectors prior to their being wired and connected to electronics in the lab, seen at the bottom of the photograph. (Ernest Orlando Lawrence/Berkeley National Laboratory)