Astronomy Chapter 8 Flashcards

The Sun: Key Facts

• A star is a glowing ball of gas maintained by gravity and powered by nuclear fusion.
• The Sun has a radius of 700,000 km and a mass of 2 x 10^30 kg.

Solar Rotation and Structure

• Solar rotation is timed by the movement of sunspots across the solar disk, taking approximately a month to complete one rotation.
• The Sun experiences differential rotation, spinning faster at the equator than at the poles.

Temperature and Atmosphere

• The Sun's temperature measures 5800 K, determined by analyzing the solar spectrum.
• The photosphere is the Sun's visible surface, approximately 500 km thick, lying above the interior layers and below the chromosphere.
• The chromosphere constitutes the Sun's lower atmosphere, while the corona is the tenuous outer atmosphere, extending into the solar wind.

Solar Energy and Internal Structure

• The Sun’s core, with a temperature of 10 million K, is where nuclear reactions occur, generating all of its energy.
• The radiation zone features high temperatures that ensure complete ionization of gas, causing photons to travel easily through this region.
• The convection zone, extending about 20,000 km below the surface, is where solar material undergoes constant convective motion.

Characteristics and Dynamics

• Ions are formed in the convection zone where hot solar gas rises outward while cooler gas sinks.
• Luminosity represents the total energy radiated by the Sun per second across all wavelengths, seen as its crucial property of light.
• Hydrostatic equilibrium in the Sun occurs when gravity’s inward pull is balanced by pressure forces.

Helioseismology and Structure

• The Sun's surface stability results from internal pressure waves that reflect off the photosphere and traverse the solar interior.
• Helioseismology studies the internal conditions of the Sun by analyzing sound waves crossing through its interior.

Density and Mass Distribution

• The Sun's highest density is found in its core, with 90% of its mass contained within the inner half of its radius.
• Energy produced in the core travels outward as radiation, while convection processes occur to transport escaped energy to the surface.

Surface Characteristics

• Sunlight manifests as visible energy, produced by convection which does not extend into the solar atmosphere due to insufficient gas.
• Granulation describes the mottled appearance of the solar surface, resulting from the interaction of rising hot material and sinking cooler material within convection cells just beneath the photosphere.