Earth is about to enter a solar wind stream that could spark polar auroras from Dec. 20th through 25th. Geomagnetic storming is most likely on Dec. 21st and 22nd with peak storm levels near G2. Sky watchers around the Arctic Circle should be alert for Northern Lights.
The source of the solar wind is a gigantic hole in the sun's atmosphere, now directly facing Earth. Earlier today NASA's Solar Dynamics Observatory photographed the structure, which covers nearly 1/3rd of the solar disk:
This is a "coronal hole"--a region in the sun's atmosphere where the magnetic field opens up and allows solar wind to escape. We've actually seen this coronal hole before--at least twice. It is rotating around with the sun, strobing Earth like a lighthouse every ~27 days. The last two times we experienced its solar wind (Oct. 25-28 and Nov. 23-26), G1- and G2-class magnetic storms sparked bright polar auroras. A repeat performance is likely in the week ahead.