Sun storm

Meet the northern lights

THIS PAST week, residents of several US states had a rare opportunity to see the northern lights bathe the sky in their eerie glow of pale green and red. The lights are normally only visible in far northern latitudes, but a surge of activity from the sun pushed them far enough south that there was even a chance we’d get a glimpse in Massachusetts. And fortunately for sky watchers, this may only be the beginning: Scientists say the sun is being roused into a period of high activity, which may bring more displays over the next few years.

The northern lights are a rare visible manifestation of space weather, the currents of matter and energy that roil above the earth’s lower atmosphere. The lights are caused by solar wind — protons and electrons streaming outwards from the sun — which can gust at speeds up to thousands of kilometers per second. When these winds push against the earth’s magnetic field, the result is a geomagnetic storm that appears to us as an aurora — arcs, sheets, or rippled filaments of light. In northern latitudes, this phenomenon is called the aurora borealis, after the Roman goddess of dawn and the Greek word for north wind. The aurora borealis only reaches the Boston area every few years; our last glimpse was in 2005.

The recent storm was created by an enormous blast from the sun called a coronal mass ejection. Although it made for some beautiful displays, it’s by no means the most impressive we’ve seen. In the summer of 1859, a huge solar flare lit up skies across Europe, the United States, and even Japan. A New York Times article from Sept. 2 that year said the northern lights in Boston were “so brilliant that at about one o’clock ordinary print could be read by the light.” That night, two operators of the telegraph line between Boston and Portland conversed for two hours powered solely by current induced by the aurora.

The sun’s cycles of activity last about 11 years on average, and after two quiet years — a longer rest than usual — the sun is stirring back into action. This means more opportunities for watching the dramatic storms it causes. In the meantime, you can see spectacular views of the sun’s activity at NASA’s Solar Dynamics Observatory website. A gallery of images of the recent aurora taken from around the world is on display at spaceweather.com, and devoted sky watchers can also sign up there for “aurora alerts” on their cellphones. Anyone who wants to track space weather conditions, including opportunities to view aurorae, can follow the National Weather Service’s Space Weather Prediction Center (swpc.noaa.gov). Should another chance come, the best way to see the northern lights is to escape city light pollution, ideally by finding a remote spot in the country with unobstructed views of the northern sky.

Courtney Humphries, author of ”Superdove: How the Pigeon Took Manhattan…And the World,” is a regular contributor to Ideas.

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Full article and photo: http://www.boston.com/bostonglobe/ideas/articles/2010/08/08/sun_storm/