An aurora (plural: aurorae or auroras; from the Latin word aurora, "sunrise") is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere. Aurora is classified as diffuse or discrete aurora. Most aurorae occur in a band known as the auroral zone, which is typically 3° to 6° in latitudinal extent and at all local times or longitudes. The auroral zone is typically 10° to 20° from the magnetic pole defined by the axis of the Earth's magnetic dipole. During a geomagnetic storm, the auroral zone expands to lower latitudes.
The diffuse aurora is a featureless glow in the sky that may not be visible to the naked eye, even on a dark night. It defines the extent of the auroral zone. The discrete aurorae are sharply defined features within the diffuse aurora that vary in brightness from just barely visible to the naked eye, to bright enough to read a newspaper by at night. Discrete aurorae are usually seen only in the night sky, because they are not as bright as the sunlit sky. Aurorae occasionally occur poleward of the auroral zone as diffuse patches or arcs (polar cap arcs), which are generally invisible to the naked eye.
In northern latitudes, the effect is known as the aurora borealis (or the northern lights), named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, by Pierre Gassendi in 1621. Auroras seen near the magnetic pole may be high overhead, but from farther away, they illuminate the northern horizon as a greenish glow or sometimes a faint red, as if the Sun were rising from an unusual direction. Discrete aurorae often display magnetic field lines or curtain-like structures, and can change within seconds or glow unchanging for hours, most often in fluorescent green. The aurora borealis most often occurs near the equinoctes. The northern lights have had a number of names throughout history. The Cree call this phenomenon the "Dance of the Spirits". In Europe, in the Middle Ages, the auroras were commonly believed a sign from God.
Alaska (i/əˈlæskə/) is a state in the United States, situated in the northwest extremity of the North American continent, with the international boundary with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait. Alaska is the largest state in the United States by area, the 4th least populous and the least densely populated of the 50 United States. Approximately half of Alaska's 731,449 residents live within the Anchorage metropolitan area. Alaska's economy is dominated by the oil, natural gas, and fishing industries; it has these resources in abundance.