OUR SUN THE CLOSEST STAR

Composition of the Sun The Sun is composed of at least 80 of the elements found on Earth. Sun is mostly composed of 91.2% Hydrogen, 8.7% Helium. The other elements make up just 0.1%. These elements include O, C, and N, and other gases present in trace amounts. All of these elements exist in the fourth form of matter called plasma – matter in which atoms have lost their electrons due to very high temperatures, basically an ionized gas.

How does the Sun produce Energy? Thermonuclear reactions occur in the core of the Sun to produce its energy. Hydrogen fuses to helium → nuclear fusion E = mc 2 Einstein’s mass-energy equivalence formula: Four H nuclei combine in a series of steps to form He. He has slightly less mass than the H from which it derived. The “missing mass” is converted into energy in the form of heat.

The Structure of the Sun

The Inner Zones

The Core Center of the Sun 10% of Sun’s diameter 15,000,000  C Sun’s gravity is so strong that the core is 10X denser than Fe. Nuclear fusion occurs here. H fuses to He resulting in energy in the form of heat.

Radiation Zone Zone surrounding the core 7,000,000  C to 2,000,000  C Photons move from atom to atom in form of waves. Their path is so slow it may take a million years for a photon to reach the surface. Radiation is the transfer of energy (heat, light, etc.) through a wave motion.

Convection Zone Energy is carried from the radiative zone to the convective zone – hot gases boil up in giant convective cells. Hot gases move the energy to the surface of the sun, then cool and sink again, ready to pick up more energy. 2,000,000  C to 5700  C.

The Sun’s Atmosphere

The Photosphere Innermost layer of the Sun’s atmosphere. Only part of the Sun we can see directly  – 6000  C. Granulation – convection cells bubble to surface and give surface a grainy appearance.

The Chromosphere Above photosphere. Called “color sphere” because of its faint reddish color. Can only be seen during total eclipse  – 100,000  C

The Corona Outermost layer of the Sun’s atmosphere. Only visible as a halo around the Sun during a total eclipse. Temperatures up to 3,000,000  C. Solar wind blows outward into space from this layer.

Activity of the Sun

Prominences Strong storms on the Sun that appear in the form of arching loops of hot gas from the Sun’s surface. Occur near sunspots. Seem to be controlled by and travel along the Sun’s magnetic field.

Solar Flares More violent than prominences Clearly linked to the magnetic field Can interfere with our radio communications & cause power blackouts Almost always near sunspot groups Particles ejected by flares and carried by solar wind can enter our atmosphere at the magnetic poles and cause auroras

Sunspots Cool, dark area on the surface of the Sun. Form in groups and may last 2 weeks to a month. Average spot twice the size of the Earth. Powerful magnetic field causes a sunspot by inhibiting circulation of gases. 11 year cycles – on average from minimum to minimum. Appear 40  to 8  above or below the Sun’s equator, but never on the equator. Sunspots move across the surface as the Sun rotates. Related to climatic problems.

The Solar Wind Hot gases of the corona blown away from the Sun. Contains mostly ionized H. Blows past the Earth at about 400 km/sec and interacts with the Earth’s magnetic field.