Alternate Definitions for Coronal Mass Ejection

An outflow of plasma from or through the solar corona. CMEs are often, but not always, associated with erupting prominences, disappearing solar filaments, and/or flares. CMEs vary widely in structure, density, and velocity. Large and fast CMEs can approach masses of 1.6 × 10^12 kg and approach velocities over 2000 km/s. Earth impacting CMEs can result in significant geomagnetic storms. Types of coronal mass ejections launched toward Earth are called "halo CMEs" because as they approach Earth, they appear larger than the Sun, making a halo of bright coronal emission completely around it.

Not to be confused with the intense burst of light that is a solar flare, a CME is a cloud of magnetized solar material that erupts from the sun's atmosphere, the corona, into interplanetary space. CMEs do often occur at the same time as a flare, and scientists currently study how the two phenomena connect. At their largest, CMEs can contain 10 billion tons of matter, and they can move at speeds of a million miles an hour. Just after blowing into space, a CME cloud can grow as wide as 30 million miles across, 35 times the diameter of the sun. When a coronal mass ejection points toward Earth, it can take anywhere from one to three days to reach our atmosphere, where it can create a type of space weather known as a geomagnetic storm.