When Wisconsin sky-watcher Brian Larmay was out for a stroll on the night of April 2, he noticed a faint glow near the North Star. Racing for his camera, Larmay captured the ethereal colors of auroras over Pembine (map)—farther south than the northern lights usually appear.
Aside from dipping into northern U.S. states such as Wisconsin and Minnesota, this early April sky show was unusual because it featured several so-called deep-sky auroras. These light shows are often faint to invisible to the naked eye but come alive in long-exposure pictures, just as astrophotographers need long exposure times to capture details in very distant "deep sky" objects such as galaxies and nebulas. (Find out how to "see" beyond the Milky Way from your backyard this month.)
To create this auroral "sunset," Larmay used a digital camera set for a 30-second exposure time.
Photograph by Brian Larmay
Ghostly green curtains of light hang over the frozen Koyokuk River in Alaska in a picture taken April 2.
Photographer Wayne Barsky drove more than 300 miles (483 kilometers) north of Fairbanks to witness auroras for the first time. Although Barsky saw just a pale green glow with the naked eye, his long-exposure shot brought out fainter blue tones higher in the atmosphere.
Two days before the sky show, a gust of solar wind had blasted off from the sun. The cloud of charged particles collided with Earth's magnetic field, and particles flowing along the field lines toward the Poles interacted with Earth's atmosphere.
Excited atoms in the atmosphere released the added energy as light, creating the streamers of faint auroras seen April 2 and 3 throughout Canada and parts of the northern United States. (Related pictures: "Solar Storms Light Up Arctic Night.")
Photograph by Wayne Barsky
Aurora's Magenta Majesty
The aurora borealis—or northern lights—appears as ribbons of purple and pink in a picture taken just north of Edmonton, Canada, on the night of April 2.
When the sun's charged particles reach the atmosphere below about 60 miles (96.5 kilometers) from Earth's surface, they mainly hit nitrogen molecules, which glow in rosy shades. More common green auroras are created by oxygen atoms between 60 and 120 miles (96.5 and 123 kilometers) above the ground.
No matter the colors, "everyone should see the Aurora Borealis at least once with their own eyes to really appreciate its splendor," photographer Zoltan Kenwell said in an email to National Geographic News.
Faint pillars of auroral light spread across the sky above northern Alberta, Canada, in a 15-second-exposure picture taken in the predawn hours of April 2.
Auroras are more common in the Northern Hemisphere during spring and autumn. One theory for why this happens has to do with the fact that the magnetic fields of Earth and the sun are constantly pushing against each other.