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# Sun

## Position in the Sky

• Motions of the Sun Simulator
• Rises East --> sets West
• Depending on the time of year, we can use the altitude to calculate the Sun's position in the sky
• Maximum height when crossing the meridian at local noon
• Local noon
• Northern hemisphere --> due south
• Southern hemisphere --> due north
• Equator --> either north or south depending on time of year
• Declination ranges between -23.5˚ and +23.5˚

## Composition

• Spectroscopic data analyzed in 1925 helped confirm composition
• Mostly hydrogen and helium
• Most elements are in the form of atoms
• So much heat, many of the atoms are ionized
• Stripped of one or more of their electrons
• Large quantity of free electrons and positively charged ions
• An electrically charged environment
• Hot ionized gas --> plasma
• Proton-proton Chain
• Core
• Extremely dense
• Source of all its energy
• Approximately 20% of the interior
• Temperature of 15 million K
• Hottest part of the Sun
• Photons carry energy and hit particles transferring energy
• How energy goes from inside --> outside
• Light from the core is transported through this zone very slowly
• High density
• Photons encounter other particles and change direction or lose some energy
• Convective zone
• Hot blobs of gas moving out
• Outermost layer of the interior
• Hydrostatic equilibrium

## Prominences, Flares, and Coronal Mass Ejections

• Prominences
• Usually originate near sunspots
• Look like loops or eruptions from the surface
• Ionized gas
• Solar flares
• Most violent event on the Sun's surface
• Rapid eruption lasting 5-10 minutes
• Releases a total amount of energy equal to that of a million hydrogen bombs
• Coronal mass ejection
• Mostly protons and electrons released from the corona
• Speeds between 500-1000 km per second

## Energy

• Outputs about $4 \times 10^{25}$ watts of energy
• When Albert Einstein discovered that mass can be considered energy, and converted into energy, the mysteries behind the Sun's power were unlocked