The Sun

Diameter – 865,000 miles Color – Yellow Star – Yellow Dwarf Mass – Earth = 1, Sun = 332,000 Surface Temperature – 12,000 degrees Fahrenheit (Hot enough to melt any known substance!) Composition- 76 % Hydrogen, 22% Helium, and about 2 % heavy elements

Jupiter Earth 3

A. Sun’s energy is generated by Nuclear Fusion - Nuclear Fusion is when the nuclei of lighter elements combine to form a heavier element -E=mc 2 (expresses that matter can be turned into energy!) - Electromagnetic energy (visible light, UV light, X-rays, gamma rays) is released - Pressure and temperature in sun 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. discovery-shorts-e-mc2-and-nuclear-fusion.htm

Hydrogen Fusion (how our Sun makes energy)

- Hydrogen has an atomic mass of Helium has an atomic mass of Hydrogen and Helium exist as plasma (charged particles) - 4 Hydrogen nuclei  1 Helium nucleus - However X 4 = ! - Einstein’s 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=MC 2 - Since there are a lot of hydrogen atoms, and the speed of light is so fast….even tiny amounts of mass become A LOT of energy! - Every second the sun produces the equivalent amount of energy created by 100 billion one megaton bombs - * 6 seconds of direct solar energy would evaporate all the Earth’s oceans - * Three minutes would melt the Earth’s crust

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 - Innermost 10% of the Sun - Nuclear fusion occurs in this layer - Temperature of about 27 million o F

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 Sun’s 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

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

15 Sunspots

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 o F) - Layer of extremely hot ionized glowing transparent gas

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

18 Suns’ Chromosphere

Sun’s Photosphere surrounded by Corona

20 Sun’s Corona as seen through an Eclipse

Very Active Corona- Photo taken during 1991 July Eclipse

A. Sunspots- a magnetically disturbed region of the photosphere that is cooler than its surroundings - May appear as single sunspots or in groups 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

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.

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

Sunspots always seem to occur in pairs. Probably due to how the kinks in magnetic field penetrate the photosphere

B. Solar Prominences - Glowing gas that erupts from disturbed regions of sunspots. T -They can be observed on the edge of the sun.

32 Solar Prominence as observed from the edge of the Sun

Unusually Large Solar Prominence as viewed by SOHO spacecraft in 1999

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

Solar Flare

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