Astronomy: The Sun, Our Star Flashcards

The Sun: Key Facts

• Surface temperature of the Sun: 5800K; central temperature: 15 million K.
• Classified as a G2V star, indicating it's an average star compared to others.
• Composition: 91.2% Hydrogen, 8.7% Helium, and 0.1% other elements.

Size and Scale

• Radius of the Sun: 109 times that of Earth, categorizing it as an average-sized star.
• Hydrostatic equilibrium: Outward pressure balances inward gravitational force, maintaining stability.

Forces at Play

• Gravity is the inward force that keeps stars together.
• Pressure force counteracts gravitational collapse, preventing the Sun from collapsing.

Energy Production

• The Sun’s primary function is to generate energy and radiate it into space.
• Energy moves from the core through three regions:
  • Thermonuclear core (where fusion occurs).
  • Radiative zone (energy is transported by photon movement).
  • Convective zone (energy is transported via convection).

Energy Transport Mechanisms

• In the thermonuclear core, fusion happens due to high temperatures and pressures.
• The radiative zone allows photons to bounce around before reaching the surface.
• Smaller stars might lack a radiative zone, relying solely on a thermonuclear core and convection.
• Larger stars may utilize a combination of thermonuclear core, convection, and radiation for energy transport.

Helioseismology and Doppler Effect

• Helioseismology analyzes seismic motions to study the Sun’s interior structure.
• Doppler effect allows observation of red and blue shifts of gases to deduce star motion and energy output.

Fusion vs. Fission

• Stars utilize nuclear fusion, combining small atoms (like hydrogen) to release energy.
• Fission involves splitting large atoms and is not a process used by stars.
• Output of energy from fusion: 4 hydrogen atoms fuse to create 1 helium atom, producing energy in various light forms, along with positrons and neutrinos.

Reaction Chains

• Smaller stars use the proton-proton chain (4 H to 1 He) for energy production.
• Larger stars utilize the CNO cycle, a six-step process reliant on catalysts that are not consumed in the reaction.

Conservation of Energy

• Energy cannot be created or destroyed but can change forms.