Lecture 10 & 11: Understanding the Sun: Structure and Energy Processes

Gravitational equilibrium

Balance between gravitational force and thermal pressure.

Nuclear fusion

Process converting mass into energy in the Sun.

Sunspots

Dark spots on the Sun's surface, active in UV light. Cooler regions with strong magnetic fields.

Coronal mass ejections

Explosive outbursts of plasma and magnetic fields from the Sun.

Luminosity

Total energy output of the Sun per second.

Radius of the Sun

6.9 x 10^8 meters, 109 times Earth's.

Mass of the Sun

2 x 10^30 kg, equivalent to 300,000 Earths.

Electromagnetic spectrum

Range of all electromagnetic radiation wavelengths.

Energy of light

Higher energy & shorter wavelength on blue side, lower energy & longer wavelength on red.

Auroras

Bright natural light (line emissions) displays caused by solar particles from coronal mass ejections. Charged particles hit Earth atmosphere (excite electrons in molecules in the atmosphere).

Solar energy emission

Sun has warmed Earth for 4.6 billion years.

Chemical energy

Energy stored in chemical bonds, not used by Sun.

Gravitational potential energy

Energy stored due to the Sun’s massive gravitational field.

Mass energy

Energy from nuclear fusion, lasts ~10 billion years.

Thermal pressure

Pressure from hot gas, balances gravitational force.

Gravitational contraction

Process where gravity compresses the Sun's core. Core contracts = heats up, temperature rises, and pressure rises. Leads to nuclear fusion.

Fusion initiation

The process in which nuclear fusion begins, occurring when the temperature, pressure, and density in a star's core are high enough for atomic nuclei to collide with sufficient energy to overcome electrostatic repulsion and fuse together.

Einstein's equation

E=mc², relates mass and energy in fusion.

Sun's age

4.6 billion years, indicates fusion duration.

Energy conservation

Energy cannot be created or destroyed, only transformed.

Sun's energy source

Primarily mass energy from nuclear fusion.

Impact of solar ejections

Can damage satellites and cause power outages.

Core

Sun's center, where nuclear fusion occurs. ~15 million K

Photosphere

Visible surface of the Sun, ~6,000 K.

Chromosphere

Middle layer of solar atmosphere, ~10^4

Corona

Outermost layer of solar atmosphere, ~1 million K.

Solar Wind

Flow of charged particles from the Sun's surface.

Helium Core

Contains 2 protons and 2 neutrons.

Carbon Core

Contains 6 protons and 6 neutrons.

Fission

Big nucleus splits into smaller pieces.

Fusion

Small nuclei combine to form a larger nucleus.

Proton-Proton Chain

How hydrogen fuses helium in Sun.

Energy Release

Fusion of hydrogen nuclei produces helium and energy.

Thermal Pressure

Pressure from heat that supports the Sun's structure.

Nucleons

Protons and neutrons involved in nuclear reactions.

Positron

Antiparticle of the electron, produced in fusion.

Solar Thermostat

Regulates core temperature and fusion rate.

Decline temp. = fusion rate drops & core contracts and heats up.

Rise temp. = fustion rate rises & core expands and cools down.

Energy Transport

Movement of energy from core to surface. Radiative & Convective.

Photon Travel Time: Sun to Earth

~8 minutes.

Energy Travel Time: Sun’s Core to Sun’s Surface

Millions of years.

Radiative Transfer

Energy moves via photons from Sun to Earth.

Convective Transfer

Energy moves through rising hot gas. Example: Spaghetti

Random Walk

Photons bounce randomly in radiation zone.

Convection Zone

Layer where hot gas rises to surface.

Photosphere

Visible surface of the Sun.

Mathematical Models

Used to predict solar interior properties. Calculate density, pressure, gravity.

Helioseismology

Vibration motions (waves) show particular patterns on the surface. The patterns depend on the density and temperature inside. Tells us what Sun is like inside.

Solar Neutrinos

Nearly massless particle emitted during fusion in Sun's core. Tells us what is happening in core.

Super-Kamiokande Experiment

Neutrinos hit electrons in water molecules and accelerates the electrons close to the speed of light.

Cherenkov Radiation

Light emitted by fast-moving electrons in water.

Solar Flares

Intense bursts of electromagnetic radiation released from the Sun's surface due to magnetic field activity.

Solar Prominences

Large, bright features extending outward from the Sun's surface.

Zeeman Effect

Splitting of spectral lines indicates magnetic fields.

Sunspot Cycle

Amount of sunspots change in 11-year cycle.

Doppler Shifts

Changes in light frequency due to motion.

Earth Seismology

Study of earthquakes to understand Earth's structure.

Magnetic Activity

Causes solar flares that send bursts of X-rays and charged particles into space and also solar prominences that erupt high above the Sun’s surface.

Luminosity of Sun

Total energy output is 3.8 x 10^26 watts.

Radiation Zone

Energy transported upwards by photons.

Convection Zone

Energy transported upwards by rising hot gas.