For the third time in two weeks, there’s a good chance you’ll be able to see the northern lights. In fact, this chance could be the best of the three.
Two coronal mass ejections erupted from the sun on Dec. 16 and are expected to reach Earth on Dec. 18 and 19.
READ MORE: WATCH: 5 of the best northern lights videos you will ever see
The U.S. Space Weather Prediction Center (SWPC) has issued a minor geomagnetic storm watch for Dec. 18 and a moderate one for Dec. 19.
Coronal mass ejections occur when the sun belches particles into space. These fast-moving particles are carried along on the solar wind and when they reach Earth, they interact with our magnetic field; we see that reaction as the northern lights.
Geomagnetic storms can also cause power disruptions and affect satellites. However, typically – unless it’s an extremely powerful storm such as the one that knocked out power across Quebec in 1989 – we won’t notice them.
Now, if you want to keep an eye on it yourself, you can visit SWPC’s Planetary K Index page, which measures the strength of geomagnetic storms. In higher latitudes with dark skies, you can usually see the northern lights when the Kp is at three. For those further south, usually you would need a Kp of four (in a dark-sky location) or higher to see them. With a minor storm the Kp will be five; with a moderate one, six.
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