NASA website reports: “…coronal mass ejection [CME] that erupted from the sun on Oct. 4, 2012 at
11:24 p.m. EDT arrived at Earth on Oct. 8 at 12:30 a.m. EDT, as observed
by instruments aboard NASA’s Advanced Composition Explorer (ACE)
spacecraft.”  CME caused geomagnetic storms when it reached Earth’s magnetosphere, resulting in Auroras. A description of Auroral mechanism at Wikipedia provides interesting details on different colors.  Ray McKenzie captured image (picture) of awe-inspiring Aurora in early hours of Oct 8, 2012 in the skies over Saskatoon, Saskatchewan.  More stunning Auroras captured for your viewing pleasure at Universe Today!