Chapter 9: Space Weather and the Sun

Sun

A ball of glowing gases consisting almost entirely of two types of gases, hydrogen and helium.

Sun's Atmosphere

The three outer layers that form the atmosphere of the Sun: the photosphere, chromosphere, and corona.

Internal Structure of the Sun

The interior regions of the Sun situated below the atmosphere, comprising the core, radiation zone, and convection zone.

Granules

Grainy structures that make up the photosphere, representing the upper part of the plasma convection zone with temperatures as high as $5\,800^\circ\text{C}$ and an average diameter of about $1\,000\text{ kilometres}$.

Sunspots

Dark regions seen on the surface of the Sun that appear dark because their temperatures are lower than surrounding granules; they are locations of very large eruptions in the photosphere, may last more than a week, and always exist in pairs or groups.

Solar Cycle

An $11\text{-year}$ recurring cycle according to which the activity of sunspots appears and disappears.

Solar Scientist

A professional who invents solar energy equipment and studies and forecasts space weather which affects daily life on Earth.

Prominence

A huge loop or arched column of glowing gases over a sunspot that can reach heights of hundreds of thousands of kilometres, lasts for days or months, and can throw out matter at speeds from $600\text{ km s}^{-1}$ to more than $1\,000\text{ km s}^{-1}$.

Solar Flare

A strong, spectacular explosion and column of charged gases erupting near sunspots; it reaches maximum brightness within seconds or minutes, dims after minutes or hours, and spouts charged gas particles into space whose light takes $8\text{ minutes}$ to reach Earth while particles take tens of minutes.

Coronal Mass Ejection

A huge expanding cloud of plasma and magnetic gas particles that erupts from the Sun, often occurring together with strong solar flares, and takes $3\text{ days}$ to reach Earth.

Aurora

A stunning light display uniquely occurring in the airspace around Earth's poles, produced when charged gas particles from solar flares or magnetic gas particles from coronal mass ejections collide and react with atoms and molecules in Earth's atmosphere.

Solar Wind

A stream of plasma particles, such as electrons, protons, and alpha particles, erupting from the Sun into outer space at supersonic speeds ranging from $250\text{ km s}^{-1}$ to $750\text{ km s}^{-1}$, carrying the interplanetary magnetic field.

Earth's Magnetosphere

A region in outer space surrounding Earth where the magnetic field is a combination of Earth's magnetic field (as the prime magnetic field) and the magnetic field in outer space brought by the solar wind.