The Sun

1. Vital Statistics: A. Diameter – 865,000 miles B. Color – Yellow C. Apparent Magnitude D. Absolute Magnitude E. Period of Rotation – About 35 days at the poles and 25 days at the equator F. Density – 1.41 G/cm3 (About the Same as the Gas Planets) G. Mass – Earth = 1, Sun = 332,000 H. Surface Gravity – 275 m/second 2 I. Escape Speed – 618 km/second J. Surface Temperature – 12,000 degrees Fahrenheit Hot enough to melt any known substance K. Composition- 76 % Hydrogen, 22% Helium, and About 2 % heavy elements (Very similar to Gas Giants)

Jupiter Earth 3

2. Sun’s Energy - A. Suns’ Energy is generated by Nuclear Fusion - Nuclear Fusion is when the Atoms lighter elements combine to form new heavier Elements. - In the process Electromagnetic Energy (Visible light, UV light, X-rays, Gamma rays) is released. - On Earth, fire also generates heat and other electromagnetic energy but fire involves the electrons of atoms only and occurs under relatively cool conditions. - In the Sun’s core the pressure and temperature are so high that it causes hydrogen molecules to move at 300 miles per second. At this speed when they hit each other, they fuse together. -In the core of the Sun, Hydrogen is being fused to make Helium This Process is called Hydrogen “Burning” So Where does the Energy come from?

- Hydrogen has an atomic Mass of Helium (Takes 4 Hydrogen’s to make a Helium) has an atomic mass of However X 4 equals ???? - Einstein’ Law of conservation of Mass and Energy states that neither Mass nor Energy can be created or destroyed….It just changes form. Therefore the difference in the mass must have become energy E=MC2 since there are a lot of hydrogen atoms and the speed of light is so large….even tiny amounts of mass become LOTS of Energy - Every second the sun produces the equivalent amount of energy created by 100 billion one megaton bombs - * Six seconds of direct solar energy would evaporate all the Earth’s oceans - * Three minutes would melt the Earth’s crust 2. Sun’s Energy (cont.)

Hydrogen Fusion (How our Sun makes Energy)

3. Sun’s structure- A. Hydrostatic Equilibrium- Balance between the forces holding the Sun together (Gravity) and the Forces trying to rip the Sun Apart (Nuclear Fusion Explosions) B. Core- - The innermost 10% of the Sun - Nuclear Fusion occurs in this layer - Temperature of about 27 million degrees F and about 20 times denser than iron. (However still a gas due to extreme temps)

3. Sun’s structure (cont.) C. Radiative Zone- - 85% of the internal mass of the Sun - Energy is transported by Radiation ( in energy waves) from the super hot interior to the cooler exterior. (This is where gamma waves change to visible light rays. Takes about a million years for a single photon to reach the surface from the core) D. Convection Zone- -Outer 15 % of the Suns’ Radius - Energy is transported by bulk motions of gas called Convection - Convection causes hotter areas of gas to rise to the surface and cooler areas to sink down into lower layers.

3. Sun’s structure(cont.) E. Photosphere- The visible “surface” of the Sun - The layer at which the density of gas becomes visible enough for us to see – Very narrow layer -”Edge” of the Sun is so sharp because of the quick transition from visibility of gases to transparency of solar atmosphere. - Atoms in this layer are constantly absorbing radiation from the hot interior. - Sunspots, Solar Flares, and Solar Prominences are formed in this layer (We will revisit these in a bit)

16 Sunspots

3. Sun’s structure- F. Solar Atmosphere- - Extremely low density gases that lie above the photosphere, consists of two main regions : - 1. Chromosphere- - Pink glowing region of gas just above the photosphere - Temperature of about 20,000 degrees F (Hot) - Can be seen by the naked eye only during a solar eclipse - Spicules- spikes of glowing gas probably due to magnetic changes 2. Corona – - Above Chromosphere – Temperature of about 3 million F - Layer of extremely hot ionized glowing transparent gas (Heat thought to come from Interactions between gas and Magnetic Field – But not sure) - Only visible during an eclipse or by viewing through a coronagraph (Machine that artificially eclipses the Sun) due to transparency of gas.

3. Sun’s structure- G. Solar Wind: - Because of very high temps its own atoms are actually able to escape the Sun’s gravity. - The mass lost is called the Solar Wind and consists mainly of electrons and atoms of hydrogen and helium. - Heliopause- Outer Boundary of the Solar Wind at a distance of about 50 AU (5 Billion Miles) from the sun

19 Suns’ Chromosphere

20 Spicules

Sun’s Photosphere surrounded by Corona

22 Sun’s Corona as seen through an Eclipse

Very Active Corona- Photo taken during 1991 July Eclipse

Coronal Mass Ejections- due to very high temps of corona, large amounts of solar material escape into space. Photo taken with a coronagraph

4. Sun’s Important Features A. Sunspots- a magnetically disturbed region of the photosphere that is cooler than its surroundings. - Appears dark only because its gases are a few thousand degrees cooler than surround gas….so it radiates less energy. - May appear as single sunspots or in groups - There seems to be about an 11 year cycle from solar minimum to maximum back to minimum 1. Cause- - due to differential rotation of Sun, the Magnetosphere sometimes develops coils and eventually kinks, which dramatically increase the strength of the field. - The strong magnetic field probably inhibits convection and thus prevents heated gas from rising up to the surface. - Eventually field collapses and resets itself to start a new cycle

27 Sunspot with Umbra at Center, surrounded by Penumbra

28

Sunspot Cycle over the Last 150 Years

Low Sunspot Activity which Coincided with Unusually cool Climate on Earth

Process of Sunspot Formation – Differential Spin rate of Sun causes the magnetic field to coil. Eventually wraps coils so tight that they kink and penetrate the photosphere.

How Sunspots form

34 Magnetic Field disrupts convection currents and prevents hot gases from rising up into photosphere

Sunspots Always seem to occur in pairs. Probable due to how the kinks in Magnetic field penetrate the photosphere

4. Sun’s Important Features (cont.) B. Solar Prominences- - Huge plumes of glowing gas that erupt from disturbed regions of sunspots. They can be observed on the edge of the sun.

38 Solar Prominence as observed from the edge of the Sun

Unusually Large Solar Prominence as viewed by SOHO spacecraft in 1999

4. Sun’s Important Features (cont.) C. Solar Flares- Gigantic Outbursts of Charged particles as well as Visible, UV, and X-rays created when extremely hot gas that spouts upward from the surface of the sun. -Usually associated with sunspots - Probably caused when the magnetic field suddenly reorganizes itself - As charged particles pass into Earth’s Magnetosphere they create Auroras. (Northern and Southern lights)

Solar Flare

43 Solar Flare

25 Northern Lights – Aurora Borealis (caused by excessive amount of charged particles hitting Earth’s Magnetosphere and exciting the gases found there