How Science Predicts the Aurora
From September until April, when the days are at their shortest and often their darkest, the Northern Lights are at their brightest. There’s no doubt that the stunning light shows, known scientifically as the Aurora Borealis (Aurora Australis in the Southern Hemisphere), are not only an item on many people’s bucket lists, but also a boon to the local economies lucky enough to have a front-row seat for the show.
For those of us who aren’t lucky enough to view the Northern Lights from our living rooms—like residents of Iceland or the Canadian Yukon—how do we know when it’s a good time to book our plane tickets and bundle up for a trip to see this spectacle? Thankfully, science can help you!
Monitoring Space Weather to Predict Auroras
Auroras exist in both the Northern and Southern Hemispheres, but the northern counterpart is far more popular for tourists hoping to catch a glimpse of the display. The Northern Lights evolve from the sun’s activity that affects the conditions in space around our star and near Earth, commonly referred to as “space weather”. NOAA scientists and forecasters at the National Centers for Environmental Information (NCEI) and the Space Weather Prediction Center (SWPC) study, monitor, and track the phenomena related to space weather and have developed methods to predict the likelihood of aurora occurrence. Click here to learn more about the space science behind the beautiful Auroras.
Being able to see the aurora depends mainly on two factors: geomagnetic activity (the degree of disturbance of the Earth’s magnetic field at the time) and your geographic location. Of course, local weather, light pollution from city lights, a full moon, and other factors can affect your viewing possibilities as well.
To know whether you have a chance of seeing an aurora, you need to know the level of geomagnetic activity occurring at the time you are viewing. The higher the geomagnetic activity, the brighter and further away from the polar regions the aurora will be able to be viewed. Space Weather forecasters at NOAA SWPC constantly monitor and forecast the geomagnetic activity, communicating its current and future levels through the G-scale. The G-scale is based on the values of the planetary K index, or Kp, that ranges from zero to nine and is derived from the maximum fluctuations of horizontal components of the Earth’s magnetic field measured by ground-based magnetometers during a three-hour interval. The current and near-future G-scale can be seen at the top of SWPC’s main webpage.
Below are maps showing the most southern extent of where aurora borealis might be observable for different levels of the geomagnetic Kp index (and G-scale). These limits are approximate, considering the averaged relationship between Kp and the auroral latitude, and indicate regions from which aurora may be visible (not necessarily overhead, but sometimes only at the northern horizon).
To access the current SWPC’s prediction of the aurora’s visibility tonight and tomorrow night, you can access the SWPC Aurora Dashboard.
After you confirm that your location is within the aurora visible region, you’ll also want to make sure you’re far enough away from a city to prevent light pollution. Check out the World Atlas of Artificial Sky Brightness: The brighter the area in this zoomable map, the harder it is to see stars and aurora in the night sky. Also, check the NOAA Weather Forecast for your area to make sure that it is not too cloudy outside. Finally, don’t forget to check out the moon phases before you go. A full moon makes it much more difficult to see an aurora because the background night sky will be brighter.
Since it is hard to forecast the Earth’s weather and space weather many weeks in advance, people that need to travel from afar to the auroral regions should consider the following information before planning their aurora hunt adventure: 1) The most favorable months to see stronger auroras are March and September, due to the best coupling between solar wind structures and the Earth’s magnetosphere around the equinoxes; 2) the best time to see auroras is around midnight (10 pm to 2 am local time); it is thus important that the aurora-hunter consider the number of hours of darkness per night at the location of interest in a particular month before traveling to the auroral region.
