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.

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