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How Old Is Our Sun?
• Stars like the Sun shine for nine to ten billion years
• The Sun is about 4.5 billion years old, judging by the age of moon rocks
The sun is a ball of glowing gas.
• Like Earth, the sun has an interior and an atmosphere
• Unlike Earth, the sun does not have a solid surface
• Sun’s mass: ~ ¾ = Hydrogen (H), ¼ = Helium (He), with trace amounts of other elements
Cross Section of the Sun
Moving from the center out:
• Core• Radiation zone• Convection zone• Photosphere• Chromosphere• Corona
Sun’s Interior: Core
• Innermost layer of interior
• Sun produces energy in its core
• Core reaches ~15 million ˚C
• Energy through nuclear fusion: 2 H atoms form 1 He + heat and light (energy)
• Heat and light move to sun’s atmosphere and into space
Sun’s Interior: Radiation Zone
• Middle layer of interior
• Region of tightly packed gas
• Energy produced in core is transferred outward through radiation zone
• Energy transferred in form of electromagnetic radiation
• Can take ›100,000 years for energy to move through it
Sun’s Interior: Convection Zone
• Outermost layer of interior
• Hot gasses move through and cool at top of convection zone
• Energy moves toward sun’s surface because loops of gas form as cooler gas sinks
The Sun’s Atmosphere: Photosphere
• The inner layer of the sun’s atmosphere—the sun’s surface layer
• Thick enough to be visible• Gives off visible light:
photos is Greek for “light”• Layer from which the light
we actually see (with the human eye) is emitted
The Sun’s Atmosphere: Chromosphere
• Middle layer of sun’s atmosphere
• Reddish glow that appears during total solar eclipse when moon blocks photosphere
• Hotter than photosphere• Chroma is Greek for color
The Sun’s Atmosphere: Corona
• Outermost layer of sun’s atmosphere
• During total solar eclipse, looks like white halo
• Extends for millions of km into space gradually thinning into solar wind
• Corona is Latin for crown
Sunspots
• Areas of gasses on surface that are cooler than surrounding gasses
• Don’t give off as much light—appear dark
• Larger in size than the Earth
• Energy sun produces changes slightly year to year (may be linked to number of sunspots)—may cause changes in Earth’s temperature
Prominences
• Huge, reddish loops of gas link different sunspot regions
• If sunspots are near edge of sun as seen from Earth, appear to extend over edge of sun
• Check out the Earth
Solar Flares
• Sometimes “loops” in sunspot areas connect
• Rapid release of energy from these localized regions on the Sun in the form of electromagnetic radiation (magnetic energy)
• The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time!
Solar Wind
• A stream of particles, primarily electrons and protons, flowing outward from the Sun at speeds as high as 900 km/s.
• Essentially the hot solar corona expanding into space.
Solar Wind Reaches Earth
• Particles enter our atmosphere at the poles
• Create powerful electric currents causing gas molecules to glow
• Can affect Earth’s magnetic field, causing magnetic storms
• Disrupt communication and cause electrical power problems