Causes of Aurora

The energy source for the aurora is 149 million kilometers (km) (93 million miles) from Earth at the sun. The sun continuously emits charged particles (mostly protons and electrons), which are the by products of thermonuclear reactions occurring inside the sun. These charged particles make up the solar wind, which travels away from the sun through space at speeds ranging from 300 to 1,000 km/sec.—about a million miles per hour. Traveling at this high speed, the solar particles can reach the Earth in two to three days.

At Earth, the steady solar wind is deflected by Earth's magnetic field, or magnetosphere. The solar wind flows around the magnetosphere much like a river flows around a stone. It also pushes on the magnetosphere and distorts it so that instead of a symmetric set of magnetic field lines—like one might have around a bar magnet—the magnetosphere is stretched and elongated into a comet shape with a long tail trailing away from Earth on the side away from the sun.

When there is a disturbance on the sun, such as a solar flare or coronal mass ejection, it can produce a disturbance in the solar wind. This in turn will cause a disturbance in the balance between the solar wind and Earth's magnetic field. As a result, electrons and protons are accelerated within the magnetosphere.

These charged particles are constrained to the magnetic field lines much like beads on a wire. The accelerated particles will travel down the magnetic field lines of Earth and collide with the atoms and molecules of the upper atmosphere where the magnetic field lines reach down to surface of the Earth near the north and south magnetic poles.

When the particles from the magnetosphere collide with the atoms and molecules of the atmosphere, the particle's energy can be transferred to the atoms and molecules (typically O, N, and N2) of the atmosphere forming excited states of O, N and N2. When these finally release their energy and return to their normal ground state, they give up energy in the form of light. This is the light that we see from the ground as an aurora.


CME’s are usually associated with solar flares and prominence eruptions. The corona is a gaseous region above the sun’s surface that extends millions of miles into space. Amazingly, temperatures in the corona may be up to 200 times hotter than the actual surface of the sun. Large bubbles of hot plasma within the hot corona are usually threaded with magnetic field lines that rise up out of one sunspot and -arch back to reconnect at another nearby spot. Sometimes, these magnetic field lines merge and cancel each other out, causing a hole in this magnetic net. The result may be as much as 10 billion tons of hot plasma ejected for several hours at speeds approaching 1 to 5 million miles per hour.

            A coronal hole based aurora

Due to the sheer speed and mass, the energy released can approach that of nearly 10 million volcanic explosions or 100 hurricanes. When an earth directed CME cloud collides with the magnetosphere, the electrons, protons, and oxygen ions of earth radiation belts become denser, hotter, and faster. The motion of these particles can produce nearly one million amperes of electrical current and disrupt the strength of earth’s magnetic field enough to allow some of the excited particles to crash into our upper atmosphere, about 40 to 200 miles above the earth. Oxygen and Nitrogen atoms react to the bombardment by becoming electrically excited and emit light. That is Aurora.


A large region in the corona that is cooler and less dense than its surroundings, as a result of open and large, weak magnetic fields are produced. A coronal hole inability to magnetically confine hot gases allows high-speed solar wind particles to be released. When a high-speed coronal stream is directed towards earth, it may result in moderate Aurora.


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