The Sun: Our Extraordinary Ordinary Star

Chapter 7: Page 235

Importance

• Early Man revered the sun – They recognized the importance of the sun to life

on earth.

• The goings and comings of the sun were carefully studied– Stonehenge

• Early Greeks – Estimated the size and distance of the sun

Average

• Mass– Not most massive or least massive

• Size– Not largest or smallest

• Brightness– Not brightest or least bright

• Just sort of “Ordinary”– But that is good for us

What we see…

• Be careful looking at the sun- never through a telescope. Use #14 welder’s glass or special coated Mylar sheets.

• We see the photosphere– Lower of 3 outer regions– Appears different depending on where we look

• During total solar eclipse we see Corona and chromosphere

Solar Granulation

Granulation in the Photosphere• Blotchy pattern = granulation• 1000 km across• Light colored areas surrounded by relatively

darker boundaries• Several million cover the surface at any time• Hot gases move upward at the center – bright• Cooler gas move downward at the edges -

darker • Convection currents bring hot gases to the

surface where they cool and sink

Center is 100 K hotter than edge

Chromosphere• Chromo = color but it is visible only during a

total solar eclipse• Dim layer of less dense stellar gas• Pinkish strip 200 km thick• Spicules – jets of gas shooting up 1000 km• 1/3 of a million at any given time covering a

few percent of the Chromosphere• Occur at boundaries of supergranules– slightly larger than Earth – contains 900 granules

1-2 million K

4000 K5800 K

10,000 K

Temperature of Outer Layers

• Move farther from a fire and temperature drops.

• Move farther from photosphere of sun and temperature increases

• Corona contains ionized gases- plasma– Electrons stripped– Iron with 13 electrons removed

• Heat from Energy carried up from the core by complex magnetic field

Solar Wind• Gas in corona is moving fast because of temperature.• Gas escapes the Gun’s gravity• Particles move out from the sun in the Solar Wind• Solar wind “protects” solar system from material

from other stars or systems• Contains– 99.9% electrons, hydrogen, helium– Silicon, sulfur, calcium, chromium, nickel, neon, argon

• Heliosphere- bubble surrounding the solar system created by the solar wind particles

Active Sun

• Sun spots and related activity• Plages (plahzh) Hotter, brighter areas– Precede sun spots

• Filaments- dark streaks• Prominences- gigantic loops or arcs• Solar Flares- violent eruptions• Coronal Holes- darker, cooler regions• Coronal Mass Ejections

Sun Spots• Observed– Chinese astronomers 2000 yrs ago– Observed by Galileo

• Explained– Cooler regions on the Sun’s surface– Umbra: Center is cooler - 4300 K– Penumbra: Cool feather region around – 5000 K– Sun’s surface - 5800 K

Center is 100 K hotter than edge

Sun Spot Cycles

• 11 year cycle– Number of sunspots increase from max to min – Location varies beginning at 30oN or S then middle

• Directly linked to magnetic field of the sun– Concentrated north or south magnetic poles

project through photosphere– Magnetic field repells ionized gases preventing

them from rising to the “surface”– Cooler and darker than surrounding area

22 year cycle

• Sun spots and sunspot groups come in pairs– Hemispheres differ– N magnetic pole points out of one and S magnetic

pole points out of the other.

• Every 11 years sun’s magnetic field reverses– For 11 years N mag points out of top hemisphere– For 11 years S mag points out of top hemisphere

11 year cycles and location of sun spots

11 year cycles and location of sun spots

Maunder Minimum

• 1645-1715 Almost no sun spots• Extreme Cold in Europe• “Little Ice Age”• Severe Droughts in Western North America• 2010- ?

Sun Spot Related Activity

• Plages (plahzh) Hotter, brighter areas– Precede sun spots

• Filaments- dark streaks• Prominences- gigantic loops or arcs• Solar Flares- violent eruptions• Coronal Holes- darker, cooler regions• Coronal Mass Ejections

Plages (plahzh)

• Very bright areas on the sun’s surface• Occur often appear just before sun spots

appear near by.

• Theory – plages are caused by magnetic fields crowding up from below and compressing the gas. Compressed gas becomes hotter and therefore brighter.

Filaments and Prominences

• Huge volumes of gas lifted upward from the photosphere by the sun’s magnetic field.

• Viewed from above the gas appears dark because it cools- filaments.

• Viewed from the side the gas looks like giant loops and arches- prominences.

SolarProminence

Solar Ejections

• Solar Wind – constant ejection of material (plasma) from the sun.– 1 million ton of material per second

• Solar flares – violent eruptions of high-energy particles lasting less than an hour.

• Coronal Mass Ejections – huge balloon-shaped volumes of high energy gas– Trillions of tons

Solar Activities and Communication

• Solar activity associated with sun spots result in massive amounts of radiation and charged particles being ejected into space.

• When this material overwhelms the protective Van Allen Belt layer of our atmosphere all electromagnetic activities can be interrupted.– Electronic communication– Electrical Distribution– Satellites

Sun Spot Update

How does the sun keep burning?• Earth has existed in its present condition for at least

hundreds of million years.• If sun were burning coal or hydrogen gas would burn

for only 5000 years.• So energy from the sun does not come from normal

combustion.• 1905 Einstein

• E= mc2 c= 3.00 x 108 m/s• c2 = 9.00 x 1016 m2 /s2

• Small amount of mass large amount of energy

Thermonuclear Fusion

• Requires very high temperatures• > 10 x 106 K• Interior of the sun 15.5 x 106 K• Hydrogen fuses to form Helium with a

decrease in mass which is converted to energy.

AppendixA

Page A-29

Neutrinos (little neutrons)• Proton Changes into a Neutron– Releases gamma ray photons– Releases a Neutrino- 1038 per second from sun

• Neutrino – Almost massless – Uncharged particle– Difficult to detect

• Detect a neutrino– If we could detect we could know what goes on in the middle of

the sun (a neutrino telescope)– Neutrino strikes a neutron changes to a proton– C2Cl4 dry cleaning fluid (carbon tetrachloride,

perchloroethylene)– Changes chlorine atom into a radioactive argon atom– Can detect radioactive atoms