It’s caused by the interaction between charged particles from the sun and the Earth’s own atmosphere.
Aurora Borealis and Aurora Australis
An aurora is an incredible light show, caused by electrically charged particles released from the sun that enter the earth’s atmosphere and collide with gases such as oxygen and nitrogen. The lights are seen around the magnetic poles of the northern and southern hemispheres.
Auroras that occur in the northern hemisphere are called “Aurora Borealis” or “Northern Lights” and auroras that occur in the southern hemisphere are called “Aurora Australis” or “Southern Lights.”
Visible in the Night Sky
If there are auroras in your region, clear nights with no wind are the best conditions for the ultimate sightings.
Aurora at Night
The lights could occur at any time from just after the sun has set in the evening to just before dawn. Auroras are often bright enough that you can see them even when the moon is out.
Aurora season in the northern hemisphere lasts from August to April. This is when the night sky is the darkest. In the southern hemisphere, the reverse is true. They are seen most often during the months of March and October.
Causes of Auroras
From time to time, electrons and protons from the sun are blown towards the Earth as “solar wind.” When the charged particles arrive at Earth, they are largely deflected by the Earth’s magnetic field.
However, the Earth’s magnetic field is weaker at either pole and therefore some particles enter Earth’s atmosphere and collide with gas particles. These collisions emit light that we perceive as the dancing lights of Auroras.
The Sun is the source of the solar winds. Sunspots and solar storms cause the most magnificent displays of the northern lights.
It takes around 40 hours for solar wind to reach Earth. Compared to light, which takes only 8 minutes to travel from the Sun to Earth.
Earth's Magnetic Field
Earth's magnetic field acts as a protective shield (kind of like water flowing around a stone in a river).
The sun rotates around its own axis once every 27 days. After a period of high northern light activity, it is common that in 27 days there will be another strong display of the aurora as the sun spots face Earth once again.
Auroras on Other Planets
Voyagers 1 and 2 were the first probes to bring back pictures of auroras on Jupiter and Saturn, and later Uranus and Neptune. Since then, the Hubble Space Telescope has taken pictures of them as well.
Auroras on either Jupiter or Saturn are much larger and more powerful than on Earth, because those planets' magnetic fields are orders of magnitude more intense.
Jupiter's aurora is a very powerful source of energy. It produces much more power (about a million megawatts) than the Earth's aurora (about 1,000 megawatts). It also never stops, because of particles coming from one of its moons.
When Voyager 2 made its flyby of the tilted planet Uranus, scientists saw what an aurora looked like on the icy blue planet. Because its magnetic field is oriented roughly vertically, but the planet rotates on its side, the aurora looks nothing like Earth’s.
Streams of charged particles blasted from the sun collide with Saturn's magnetic field, creating an aurora on the planet's south pole.
Aurora’s Size and Color
The lights of the Aurora generally extend from 50 miles to as high as 400 miles above the earth’s surface.
As auroras are the result of collisions between gaseous particles in the Earth’s atmosphere with charged particles from the sun, variations in color are due to the type of gas particles that are present.
International Space Station
The International Space Station, on occasion, travels through the Northern Lights, which are in its orbit.
Visible from Space
Should life exist on other planets in the solar system, in theory they would be able to see the auroras shining on the Earth's night side. Even studying the aurora from space can provide more information about the sun.
Disruptions and Interferences
Intense northern lights activity can interfere with radio, satellite and GPS signals, and sometimes shut down power networks.
The rarer red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purple auroras.
The most common aurora color which is green, is produced by oxygen molecules located about 60 miles above the earth. While aurora can occur at any time, they are just not bright enough to be visible during the day.
The Shape of the Aurora
Auroras can appear in many forms, from small patches of light that appear out of nowhere to streamers, arcs, rippling curtains, or shooting rays that light up the sky with an incredible glow. The auroras that occur most commonly appear as a faint glow across the sky.
The phenomenon occurs in a part of the atmosphere where air density is extremely thin. Due to the thin air density, temperatures within the lights end up being several degrees Celsius below zero.
Shapes of Auroras
The lights of the aurora may manifest as a static band of light. However, when the solar flares are particularly strong, they may appear as a dancing curtain of ever-changing color.
While some cultures took the swirling light show as a bad omen, most saw it as an unusual and impressive display, and came up with many stories to interpret this natural phenomenon.
The Laplanders, a group of arctic indigenous peoples, believed auroras were calming, so they used the time when they could be seen for conflict resolution. They also believed that if you whistled under auroras, you could summon them and they would take you away.
The Norwegians believed the auroras were the merrily dancing and waving spirits of old maids.
Eskimos saw similar connections in the auroras to dancing. For example, in Eastern Greenland, the eskimos believed the lights were caused by the dancing spirits of children who had died at birth.
Greek and Roman Writings
The northern lights were so rare in some parts of the world that in ancient Rome and Greece, they saw the lights as the result of the heavenly battles of ancient heroes. They also viewed auroras as ominous signals of war and sickness to come.
The Algonquin Indians had the belief that Nanahbozho the Creator travelled north after he created the world, and continues to build great fires there. These fires reflected south to serve as a reminder of his love for his people.
Auroras on Earth
As the magnetic south pole is in Antarctica, unless you are a scientist working there, it usually leaves the northern hemisphere the most sensible option of viewing an aurora. Northern parts of Canada, particularly the Yukon, Nunavut, Northwest Territories, and Alaska are best.
In Europe, Scandinavia, particularly the Lapland areas of Norway, Sweden, and Finland are very good for aurora viewing. Iceland is also a good place for auroras as well as the southern tip of Greenland.
The bright dancing lights of the aurora are actually collisions between electrically charged particles from the sun that enter the Earth's atmosphere.
Scientists have learned that in most instances the northern and southern auroras are mirror-like images. In fact, they occur at the same time, often providing lights displays of similar shapes and colors.
Low on the Horizon
Generally speaking, the further away from the pole you are, the lower on the horizon the aurora will be.
Auroras are not visible through most types of clouds from the ground, because clouds are much lower than auroras.