A recent upsurge in activity on the surface of the sun gets credit for last week's display of the northern lights, one of the best in Utah in recent memory.

Patrick Wiggins, Hansen Planetarium's education specialist, said the aurora borealis - as the phenomena are officially know in the Western Hemisphere - appear as pulsating curtains, patches or streamers of light in the northern sky.The lights appear when fast-moving particles from the sun, known as a solar wind, strike the Earth's upper atmosphere. When gases in the air are struck by the solar wind they glow. The color of the glow depends on the energy level of the solar wind.

Blue and red results from nitrogen being struck by high-energy solar wind at about 110 kilometers altitude. More common green auroras result from collisions with oxygen between 110 and 250 kilometers up. A steady red glow results from oxygen collisions with relatively low-energy particles at 300 to 400 kilometers above the Earth's surface.

Wiggins said auroral displays occur almost every night near the Earth's magnetic poles, but far less frequently at locations distant from the poles. On average, northern Utah can expect to see one or two displays per year. In southern Utah, displays are seen even less often.