AuroraWatcher

About aurora and this page

What aurora is

Aurora is light from oxygen and nitrogen high in the atmosphere, 100 to 300 km up, struck by particles guided in along Earth's magnetic field. It forms a ring around each magnetic pole. Most nights it stays at high latitudes; during a geomagnetic storm the ring widens and moves toward the equator.

What makes a storm

Most strong storms follow a coronal mass ejection, a cloud of solar plasma that takes one to four days to reach Earth. Its arrival shows first as a jump in solar wind speed at the L1 monitors. Whether it drives a storm depends mostly on Bz: a long southward stretch gives a strong display, a northward one can give little.

How the cams are chosen

The page checks every cam on the SnowGrabber network every 10 minutes. A cam is shown when the sun is more than 12 degrees below its horizon and its latest frame looks like a night sky: a dark upper half with points of light that read as stars, and no floodlights or daylight. Cams with more stars, wide panoramic views and a record of clear nights rank higher, and cloud cover from the forecast is shown beside each one. During a storm, cams under NOAA's aurora forecast move to the top.

Each cam is marked Live when its latest image is as recent as its usual interval allows, or Late when it has fallen behind. Cams with no new image for three hours are left out. Panoramas whose compass direction is known are cropped to the 150 degrees facing the nearer pole, where aurora shows from mid-latitudes, and the star count is for that part; the full panorama opens on click.

"Dark left" on each cam is the time until dawn there, when the sun comes back to 12 degrees below the horizon and the sky starts to brighten; hover it for dawn and sunrise in local time.

Cams take a single frame every 10 to 60 minutes, so they show a steady glow well and short bursts or meteors only by chance. Faint aurora often shows more clearly on a camera than to the eye, as a green or red band low on the poleward horizon.