Space Astronomy

Sun

• Diameter is about 1.5 million kilometers
• Orbits around the center of the Milky Way Galaxy around 225-250 million terrestrial years
  • Known as a galactic or cosmic years
• Follows the ecliptic on the celestial sphere
• Accounts for 98.6% of the Solar System's mass
  • 98% of its mass is hydrogen and helium
• Surface temperature is ~5800 kelvin
• Energy produce with fusion
  • Hydrogen --> helium
• Brighter than ~80% of the stars in the Milky Way Galaxy

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˚

Atmosphere

• Photosphere
• Chromosphere
• Transit region
• Corona

Composition

• Spectroscopic data analyzed in 1925 helped confirm composition
  • People originally believed it must be Earth-like
  • Analyzed by Cecilia Payne-Gaposchkin
    • She suggested the Sun was composed mainly of hydrogen and helium
• Mostly hydrogen and helium
  • ~73% hydrogen
  • ~25% 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
  • Only happens in the centre of the Sun
• Hydrostatic equilibrium

Core

• Extremely dense
• Source of all its energy
• Approximately 20% of the interior
• Temperature of 15 million K
  • Hottest part of the Sun

Radiative Zone

• 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

Solar Activity

• Prominences
• Solar flares
• Coronal mass ejection

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