Northern Lights

Executive summary by darmansjah

The aurora borealis forms a 2,000 mile wide (3,219 km) oval over the North Pole.

ARTIC CIRCLE The northern lights, or aurora borealis, forms in the rolling interior of the sun. the atoms that make up solar gases are transformed into a thin stream of electrically charged particles-protons and electrons. This stream, the solar wind, is both matter ad energy. It continuously erupts from the sun. most of the solar wind sideswipes the Earth’s magnetic shield, but some spirals down toward the planet’s north and south magnetic poles, where it churns the oxygen and nitrogen in the atmosphere. Shades of green, red, bright pink, blue, or violet appear depending on how far from Earth the electrons and nitrogen molecules interact.

An Audience of One

Residents of Alaska, such as this woman in Anchorage, know that the best time to view the northern lights is during long midwinter nights, when the sun is at “solar maximum”-the period of greatest activity in the solar cycle.

Dancing Lights

Auroral displays swirl in the skies above Alaska’s Portage Lake and Bleik, Norway. Greenish-white is the most typical auroral color.

Celestial Fireworks

Colliding with atmospheric gases, charged solar particles create an infinite variety of auroral displays. Variations in altitude, type of gas, intensity of solar wind, and position of the observer affect the appearance of an aurora.

Explained by science

The Earth’s magnetic field forms a protective envelope called the magnetosphere. Arriving with great force, the solar wind compresses the front end of the magnetosphere and elongates the back end into a tail. At the point of impact, if properly aligned, the solar wind’s magnetic field links up from Earth. This connection produces the auroras seen on dark winter days in the extreme north and south latitudes. As it blows by the Earth, the solar wind peels back the planet’s field lines now linked to it. When those lines reach the tail of the magnetosphere, they break away from the solar wind and reconnect. Scientists still do not fully understand how, but this process of reconnection transforms magnetic energy into kinetic energy, which then propels electrons and positive ions into Earth’s atmosphere along the newly reconnected field line. These speeding particles, especially the electrons, create the nighttime auroras. Crashing into the atmosphere, electrons hit the atoms and molecules of gases such as oxygen and nitrogen. In each collision, the atom or molecule absorbs energy from the electron, then releases the light. Color depends on which gas is hit and at what altitude.