Explanation: Dramatic prominences can sometimes be seen looming just beyond the edge of the sun. Such was the case last week as a large prominence, visible above , highlighted a highly active recent Sun. A waving sea of hot gas is visible in the foreground chromosphere in great detail as it was imaged in one specific color of light emitted by hydrogen. A solar prominence is a cloud of solar gas held just above the surface by the Sun's magnetic field . The Earth , illustrated in the inset, is smaller than the prominence . Although very hot, prominences typically appear dark when viewed against the Sun , since they are slightly cooler than the photosphere below them. A quiescent prominence typically lasts about a month, and may erupt in a Coronal Mass Ejection (CME) expelling hot gas into the Solar System , some of which may strike the Earth and trigger auroras .