Auroras

An Introduction

An aurora is a colorful glow that appears in the sky at night. Most auroras appear in the far northern and southern parts of the world. Auroras in the northern part of the world are called the northern lights. The colored lights appear as curved lines, clouds, and streaks. Some auroras move or get brighter or flicker suddenly. The most common color in an aurora is green, but sometimes auroras are red or purple. Auroras form when the solar winds reach the Earth. The solar winds are a flow of particles, or tiny bits of matter, from the sun. The particles in solar winds contain electrical energy. When these particles strike other particles that surround the Earth, energy is released. Some of this energy appears in the form of auroras. 

How the Auroras Form

The auroras form when charged protons and electrons emitted from the sun (solar wind) penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. These collisions result in countless little bursts of light, called photons, which make up the aurora. Collisions with oxygen produce red and green auroras, while nitrogen produces the pink and purple colors. This reaction encircles the polar regions of the earth and occurs at an altitude of 40-400 miles (65-650 km) in a zone called the "Auroral Oval." 

When & Where

The auroras most commonly occur between 60°-75° latitude, but during great geomagnetic storms the auroral oval expands equatorially and can reach 30° latitude or further. In the northern hemisphere they are called the aurora borealis (northern lights) and in the southern hemisphere aurora australis (southern lights). An auroral display might be observed any night from dusk until dawn as long as it is dark, which excludes Alaskan summer nights (May-July). The best time to view them is between midnight and 2 am. There is an 11-year solar cycle (on average) that controls the tempo of the aurora. The most recent peak in the cycle occurred in 2000-2001. The next peak is predicted in 2011.