The Nearest Star

A very average sort of star

• mass 2.10^33 gm<=>300,000 Earths <=> 1000 Jupiters
• diam. 865,000 mi <=> 109 E <=> 10 J
  cf. if E is a dime, sun is 6.5 feet
• surface temp 6,000 K
• composition: H (74%), He (25%), everything else (1%)
• luminosity 4.10^33 ergs/s <=> 4.10^26 watts
  would light 10^21 Scott Stadiums
  E catches ~10^18 KWh/yr , 1,370 W/sq.m
  

Normal, Quiet Sun

• Photosphere
  
  • granulation (bubbly surface)
    ~1000 km, time scale several minutes
  • limb darkening
• Chromosphere
  spicules
  rise 45,000 mph to 6,000 miles
  edge of supergranules
• Corona
  see during eclipse, with coronograph
  
  • 2 million degrees,
  • highly ionized, eg FeXIV
  • v.low density;
  • heating mechanism?

Features of Activity cycle

• Sunspots
  
  • single, N-S pairs, and groups
  • 6,000 mi diam, 1000 deg cooler
  • umbra, penumbra
  • show differential solar rotation
  • magnetic fields ~5000 Gauss, Zeeman effect
  • solar cycle, 11 yrs (22 yrs with reversal)
    Maunder minimum 1645-1715; Little Ice Age
    longer period variations?
    
• Plages
• Filaments, prominences
  50,000 deg, 100,000 miles high
• Solar Flares
  5 million deg, 10^25 J (2 billion megaton bomb)
  energy arrives at E in 8.3 min
  particles arrive ~2 days <=>aurora, ionospheric disturb.
  
• X-rays
  coronal holes, bright spots

Solar energy

   Sun has been around for 4.5 billion years. What could produce
   such prodigious quantities of energy?
   
   Chemical energy: coal/oxygen would last ~5,000 years
 
   Kelvin-Helmholtz (gravitational) contraction
      energy goes about half to temperature, half to light
      need contraction of about 120 feet/year
      could go about 50 million years
 
   thermonuclear fusion