The Sun & Stars - Notes

Vocabulary

  1. Photosphere - Visible surface of the Sun

  2. Chromosphere - A reddish gaseous layer immediately outside the photosphere of the sun or another star.

  3. Corona - The rarefied gaseous envelope of the sun and other stars. The sun's corona is normally visible only during a total solar eclipse when it is seen as an irregularly shaped pearly glow surrounding the darkened disk of the moon

  4. Solar wind - The continuous flow of charged particles from the sun that permeates the solar system.

  5. Sunspot - A spot or patch appearing from time to time on the sun's surface, appearing dark by contrast with its surroundings.

  6. Solar flare - A sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group.

  7. Prominence - A large, bright, gaseous feature that appears above the surface of the Sun and extends into the corona.

  8. Fusion - The process by which multiple nuclei join to form a heavier nucleus, with the release or absorption of energy.

  9. Fission - The splitting of a heavy, unstable nucleus into two lighter nuclei.

The Sun

  • The Sun's diameter can fit 109 Earths lined up.

  • The Sun’s mass is 330,000 times Earth's.

  • The Sun contains over 99% of the solar system's mass, affecting planetary motion; equivalent to 1048 Jupiters in mass and 10 in diameter.

Composition of the Sun

  • Made of Hydrogen (92%) and Helium (7%).

Layers of the Sun (Inside Out)

  1. Core

    • Center of the Sun; contains most of its mass (VERY dense).

    • Made of PLASMA; area where nuclear fusion occurs.

    • Temperatures reach millions of degrees Celsius.

  2. Radiation Zone

    • Very thick - 300,000 km.

    • Light emitted from the core scatters; photons can take up to 1 million years to pass thru.

  3. Convection Zone

    • Gaseous layer reaching the Sun's surface.

    • 200,000 km thick

  4. Photosphere

    • Visible surface; 400 km thick.

    • 5800 K

    • Innermost layer of Sun’s atmosphere; most visible light comes from here.

  5. Chromosphere

    • 2500 km thick

    • 15000 K

    • Outside the photosphere; visible only during solar eclipse (red due to emissions in red wavelengths); most emitted radiation: UV

  6. Corona

    • Outermost layer, extends several km outside Chromosphere.

    • 3 to 5 million Kelvin

    • Seen during an eclipse; most-emitted radiation: X-rays

Solar Wind

  • Plasma flows outward from the corona.

  • Consists of charged particles (ions).

  • Deflected by Earth’s magnetic field, trapped by Van Allen belts.

  • The particles collide with atmospheric gases, causing aurora.

Solar Activity

  • Magnetic Field and Sunspots: Magnetic field disturbs the solar atmosphere.

    • Causes sunspots (dark spots on the photosphere).

    • Sunspots are cooler in temp, located where MF penetrates the photosphere.

  • Coronal holes: Low-density areas in the corona where solar wind escapes.

  • Solar flares: Violent eruptions of particles and radiation.

    • Particles escape in solar wind, affecting satellites and radio communication a few days later.

  • Prominence: Arc of gas ejected from the chromosphere or condensed gas in the inner corona.

    • Lasts hours to months; CMEs disrupt satellites, power grids, navigation, and increase geomagnetic storms.

Nuclear Fusion

  • ²H: Deuterium, an isotope of hydrogen with one proton and one neutron.

  • ³He: Helium, a heavier element with two protons and one neutron.

  • ⁴He: Helium, a heavier element with two protons and two neutrons.

Nuclear Fusion (3 main steps)

  1. 2 protons form deuterium, a positron, and neutrino

    • 1H + 1H → 2H + e+ + v\text{1H + 1H → 2H + e+ + v}

    • (p++p+)→(p+n0)+e+ and v(p+ + p+) → (p+n0) + e+ \text{ and } v

  2. Deuterium and a proton form helium, and energy in the form of gamma ray

    • 2H + 1H → 3He + energy\text{2H + 1H → 3He + energy}

  3. 2 helium-3s will form helium-4 and protons

    • 3He + 3He → 4He + 1H + 1H\text{3He + 3He → 4He + 1H + 1H}

Nuclear Fission

  • Stars primarily produce energy through nuclear fusion.

  • Plays a role in star evolution by creating heavy elements (ex. gold).

  • Fission occurs when a heavy nucleus (like uranium) splits, releasing energy.

  • Occurs in extreme conditions like neutron star mergers or supernovas.

Step-by-Step Journey of Energy

  1. Core: Fusion begins, producing gamma rays and neutrinos.

  2. Radiative Zone: Energy moves slowly by radiation.

    • It can take thousands to millions of years for energy to pass through this zone.

  3. Convection Zone: Energy moves more quickly via convection.

    • Hot gases rise, cool, and sink—this motion carries energy to the surface.

  4. Photosphere: The Sun’s visible surface.

    • Energy escapes as visible light, infrared, and other types of electromagnetic radiation.

  5. Through Space to Earth: Light and energy travel through space as electromagnetic waves.

Lesson 2: Life Cycle of Stars