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GEOMAGNETIC STORM WATCH: Earth's magnetic field remains unsettled following the impact of a CME on Sept. 17th (described below). NOAA forecasters say there is a chance of G2-class geomagnetic storms on Sept. 18th as Earth passes through the CME's wake. Aurora alerts: SMS Text.

THE AFTERGLOW OF A 'WEAK' CME: Yesterday, Sept. 17th (0200 UT), a long-awaited CME hit Earth's magnetic field. The impact was weak, lifting the solar wind speed by a measly 40 km/s. Despite such a feeble blow, the CME managed to stir geomagnetic activity hours later when Earth encountered magnetic fields in the CME's wake. Evan Zucker filmed the display from High Level, Alberta:

"At first we saw little more than a dim green glow in the northern sky," says Zucker, who watched the show with his wife. "At around 4:00 AM MDT, however, the aurora became increasingly active, culminating in by far the brightest display we have ever seen. Auroras stretched from horizon to horizon. It was exhilarating! "

Zucker's story shows why even weak CMEs are eagerly anticipated by aurora photographers. CMEs of all sizes drag solar magnetic fields behind them. These fields can link up with Earth's own magnetic field, opening cracks for incoming solar wind. The resulting afterglow can be very beautiful, indeed. Now imagine what a strong CME could do. Aurora alerts: SMS Text.