Interpreting the Aurora

The auroral activity forecast predicts the expected location of the most active auroral forms that can be expected for the given period. Aurora viewing is also affected by a variety of other factors, such as cloud cover, moonlight, and urban light pollution, so what you see will be strongly affected by your particular location and meteorological luck. The best time to observe aurora is near local midnight, when the most active forms often occur. More precisely, the time to shoot for is an hour or two prior to local geomagnetic midnight, and the forecast maps found here are calculated for that time. If you are a serious aurora watcher, plan to spend the night from about 9 P.M. to 3 A.M. watching for auroral action. Auroral activity tends to come in waves during an evening, which are called auroral substorms. Even during an active period, there will be lulls in which the auroral activity is subdued; however, the patient observer will often see a new burst of activity within an hour or two. The auroral forecasts categorize auroral activity as follows:

(Select a view:  )

Kp=0: Minimum Auroral Activity

Kp=1: Quiet Auroral Activity

Kp=2: Low Auroral Activity

Kp=3: Moderate Auroral Activity

Kp=4: Active Auroral Activity

Kp=5: High Auroral Activity

Kp=6: High+ Auroral Activity

Kp=7: High++ Auroral Activity

Kp=8: High+++ Auroral Activity

Kp=9: Maximum Auroral Activity

Note that the shaded areas refer to the locations where the aurora will be overhead. Because the auroral forms are more than 80 km (55 miles) above the earth, you may see them from as far as 400 km (250 miles) away. The green line equatorward of the main auroral zone identifies the region where aurora can be seen on the horizon. The forecasts deal with the average level of activity expected within the prediction period. The sun occasionally produces bursts of unforeseen intensity, so the most spectacular auroral displays can come with little warning. Note that there are three different forecasts on the home page. The long term forecast (Active, Medium, and Quiet) is our guess as to the general level of activity during the next 28 days (one solar rotation). Use this forecast to plan a trip to the auroral zone. The main forecast (0 to 9 levels corresponding to the planetary magnetic index, Kp) is our best estimate for the next 3 to 7 days. Use this in combination with the weather forecast to plan your aurora watching schedule. The short term forecast (0 to 9 levels) is a calculation based on measurements of the solar wind made at a satellite that is approximately one hour upstream toward the sun. Watch this forecast from the comfort of your chair to find out when you should wake up the kids and go outside to see the display from a place away from city lights with a good view of the horizon toward the pole. For more information on the aurora, consult The Aurora Watcher's Handbook by Neil Davis (ISBN 0-912006-60-9). The extent of auroral activity as it is right now and in the recent past may be accessed at The extent of auroral activity as it is expected within the next hour can be viewed here.

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