The Sun

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

The Sun’s Interior

• Core

• Radiation Zone

• Convection Zone

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

• Chromosphere

• Corona

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

Features on the Sun

• Sunspots

• Prominences

• Solar Flares

• Solar Wind

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

Solar Center Stanford University

The sun rotates!• The sun rotates once every 27 days

• Different parts of the sun rotate at different speeds

http://science.nasa.gov/ssl/pad/solar/sunturn.htm