LUNAR IMPACTS TODAY: NASA's twin lunar gravity probes, nickhamed Ebb and Flow, will collide with a mountain near the Moon's north pole today, Dec. 17, at 5:28 pm EST. Get the full story from Science@NASA.
SOLAR WIND: Earth is entering a stream of high-speed solar wind. The source of the wind, a coronal hole on the sun, is shown in this image taken by NASA's Solar Dynamics Observatory during the early hours of Dec. 17th:

A coronal hole is a place in the sun's atmosphere where the solar magnetic field opens up and allows solar wind to escape. This particular coronal hole is located far down in the sun's southern's hemisphere, so the stream it is emitting is not heading directly for our planet. To some degree, this will mitigate its impact on Earth. At the moment, NOAA forecasters are estimating a relatively slight 20% chance of geomagnetic storms. Nevertheless, high-latitude sky watchers should be alert for auroras. Aurora alerts: text, voice.
Realtime Space Weather Photo Gallery