What are Coronal Mass Ejections?
The Sun can be a violent place. Its photosphere -- the layer of gas we perceive as its "surface" in visible light -- contains a bubbling mixture of material at roughly 5600 degrees Kelvin. Stretching out into space above the photosphere is the corona, a region of gas which is less dense than the photosphere (so that emits much less light), but extremely hot: up to a million degrees Kelvin. Every now and then, a titanic disturbance in this part of the Sun sends a blob of material flying outward at millions of kilometers per hour. We call these Coronal Mass Ejections, or CMEs for short.