Astronomy Magazine
Glossary · The Sun & Space Weather
Coronal mass ejection
Also written CME
A billion tonnes of solar atmosphere thrown into space, and the cause of most serious aurorae.
A coronal mass ejection is a great bubble of magnetised plasma launched off the Sun when its magnetic field reconfigures. If one is aimed at Earth it arrives one to three days later and slams into our magnetic field, compressing it and dumping energy into the upper atmosphere: aurorae far from the poles, disturbed radio, extra drag on satellites, and induced currents in long conductors like power grids and pipelines. The Carrington event of 1859 set telegraph offices on fire. A repeat would be considerably more expensive now, which is why several spacecraft do nothing but watch the Sun for these.
Where it has come up lately
Phys.org
Phys.org
NASA Science
AAS Nova
Related terms
Solar flare classes
A, B, C, M, X — a logarithmic scale for how hard the Sun just flashed in X-rays.
Kp index
A 0–9 scale of how disturbed Earth's magnetic field is right now.
The solar cycle
An eleven-year rhythm in sunspots, flares and the Sun's entire magnetic field.
Sunspot
A patch of the Sun where the magnetic field is strong enough to hold the heat back.
Questions
What is Coronal mass ejection?
A billion tonnes of solar atmosphere thrown into space, and the cause of most serious aurorae.
Why does it matter?
The Carrington event of 1859 set telegraph offices on fire. A repeat would be considerably more expensive now, which is why several spacecraft do nothing but watch the Sun for these.