Physical Science 101
The Sun


Atoms - the smallest particle of an element which can enter into a chemical combination
Periodic Table of Elements - list of all known elements
Atoms can be broken down into smaller parts
Requires nuclear reactions or electromagnetic interactions to breakdown an atom

Atomic Structure

Three subatomic particles
Protons -
Neutrons -
Electrons -
Protons and Neutrons are found in the __________.
Electrons are found in _________________________.

Atomic Number

Atomic Number is the number of protons in the nucleus
All atoms of the same element will have the same number of protons
Atomic Symbol is the letter designation for a given element
C - Carbon O - Oxygen Cl - Chlorine
Na - Sodium (natrium)
Fe - Iron (ferrum) Au - gold (aurum)

Atomic Mass

Atomic Mass is the sum of the masses of all atomic particles
proton - 1.6 x 10-27 kg
neutron - 1.6 x 10-27 kg
electron - 1 x 10-30 kg
Atomic Mass Number is based on each proton and neutron having a mass of 1


What is the atomic mass number for Oxygen on the Periodic Table of Elements?
Every oxygen atom must have 8 protons
The number of neutrons in the nucleus can change

The Sun

General Structure
Corona: 1 million K, few million km above surface
Chromosphere: 10,000 K, near the surface
Photosphere: 5,800 K, visible surface
Sunspots: darker areas on the surface
Convection Zone: Energy travels to the surface by convection, gas becomes plasma at greater depth
Radiation Zone: 10 million K, Energy transmitted by photons - radiation
Solar Core: 15 million K, Nuclear fusion converts hydrogen into helium

Sun Power

What powers the Sun?
What is the difference between nuclear fission and nuclear fusion?

Fission vs. Fusion

Nuclear Fission -
What happens to the element?
235U → 90Ru + 143Cs + 2 neutrons
Nuclear Fusion - combines two smaller nuclei into a single, larger nucleus
What happens to the elements?

Hydrogen Fusion

High pressure and temperature in the solar core
Hydrogen nuclei are moving quickly, colliding with other hydrogen nuclei.
Hydrogen fuses to helium.
41H ® 4He + energy
However, the collision of four hydrogen at the same time is rare.

Proton-Proton Chain

Step 1: Two protons collide and fuse to form deuterium (1p, 1n)
1H + 1H → 2H + e+ (positron)
Step 2: Deuterium nucleus collides and fuses with a proton to form Helium-3 (2p, 1n).
2H + 1H → 3He + gamma ray
Step 3: Two He-3 collide and fuse to form Helium-4.
3He + 3He → 4He + 2 protons

Missing Mass

The 4He nucleus has a smaller mass than the 4 hydrogen nuclei that went into making it.
Every second the Sun fuses 600 million tons of hydrogen into 596 million tons of helium.
What happened to the missing 4 million ton mass?

Solar Theromostat

Self-regulating fusion: due to changes in temperature and pressure.
As the temperature goes up, fusion reactions increase.
More energy is released and the pressure goes up.
As the pressure increases the core expands.
This causes the core to cool, fusion slows.
As the core cools, fusionreactions slow.
As fusion slows, pressure decreases causing the core to collapse under the influence of gravity.
As the core collapses, the pressure increases and the temperature goes up.
Fusion reactions increase.

Solar Oscillations

These increases and decreases in the size of the core create pressure waves.
These seismic waves cause the Sun to quake and vibrate.
Just as seismic waves on Earth show us what the interior of the Earth is like, analysis of solar oscillations tell us what the interior of the Sun is like.

Solar Interior

Fusion energy is produced in the solar core.
Photons slowly move outward radiative diffusion through the Radiation Zone.
Gamma rays become visible radiation as the energy levels decrease.
Energy is then transported towards the surface by convection in the Convection Zone.

Solar Surface

The radiation finally leaves the Sun at the Photosphere - the surface of the Sun.
The Photosphere shows a number of features including granulations, sunspots, solar prominences and solar flares.


The surface has a mottled appearance


Darker areas on the surface
Created by twists or loops in the Sun's magnetic force lines that intersect the surface

Prominences and Flares

Solar Prominences loops in the magnetic force lines that break through the surface (forming sunspots)
Charged particles are trapped within the loops
Solar Flares - twisted magnetic force lines break apart releasing huge amounts of energy - x-rays and accelerated charged particles

Sunspot Cycles

Sunspots cycle from a solar maximum to a solar minimum with an average period of 11 years
Cycle begins at a solar minimum:
Cycle ends at the next solar minimum:

Magnetic Reversals

At the sunspot cycle maximum:

Sun Rotation

The Sun's rotation is not equal
The equator rotates once every 25 days
The poles rotate once every 30 days
This unequal rotation warps the magnetic field
Eventually causes the magnetic field to break down