Our Star, the Sun

The Sun is the Largest Object in the Solar System

• The Sun contains more than 99.85% of the total mass of the solar system

• If you put all the planets in the solar system, they would not fill up the volume of the Sun

• 110 Earths or 10 Jupiters fit across the diameter of the Sun

How big is the Sun?

An X-ray look at the Sun.

http://bcs.whfreeman.com/universe6e/pages/bcs-main.asp?v=category&s=00110&n=01000&i=18110.07&o=|18000|01000|&ns=0

The Sun goes through periods of relative activity and inactivity

The Sun’s interior has three layers:(1) core(2) radiative zone (3) convective zone

Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes tens of thousands of years or more.

The Sun’s atmosphere also has three layers…

• Photosphere - the layer we see, 5800 K

• Chromosphere - the red layer observed using a hydrogen filter, 10,000 K

• Corona - the incredibly thin outer atmosphere, 1,000,000 K

The photosphere is

the visible layer of the

Sun

Granulation caused by convection

http://www.whfreeman.com/universe6e - Seething Granules around a Sun Spot

Sunspots are the most well known feature in the photosphere. Monitoring sunspots reveals the

Sun’s rotation.

http://www.whfreeman.com/universe6e - the motion of a small sun spot

The movement of

sunspots reveals that the Sun’s

rotation takes about …

4 weeks

Maximum number

Minimum number

The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle

Magnetic field lines connect sunspots on the Sun’s photosphere

Above the photosphere, the chromosphere is characterized by its red color –

from H emission.

Solar magnetic fields also create other atmospheric phenomena

• prominences

Solar magnetic fields also create other atmospheric phenomena

• prominences

• solar flares

The corona, the outermost part of the Sun’s atmosphere, is characterized by its high

temperature and low density

The Sun also ejects a stream of charged particles into space known as the solar wind

Solar magnetic fields also create other atmospheric phenomena

• prominences

• solar flares• coronal mass

ejections (CMEs)

http://www.spaceweather.com/

http://www.spaceweather.com/images2002/18mar02/cme_c3_big.gif

The most powerful solar flare in 14 years, .. erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

The Earth’s magnetic field is caused by movement of material in Earth’s interior

The Earth’s magnetic field produces a magnetosphere that deflects and traps

particles from the solar wind protecting Earth

Relevance of Earth’s protective magnetosphere

• Protects against Solar Flares - violent explosions on the Sun releasing large burst of charged particles into the solar system

• Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun

• Northern Lights (Aurora Borealis)

Northern Lights (Aurora Borealis)

As the charged particles from the Sun interact with the magnetic field around Earth, the particles collide with the nitrogen and oxygen atoms in the atmosphere and excite those atoms to emit light

See Mastering Astro animation

Aurora as seen from space