Saint Elmo’s Fire

Cloud of the Day – Saint Elmo’s Fire

Image credit – Wikimedia

Saint Elmo’s fire is sometimes confused with ball lightning, but the two phenomena are quite different. While Saint Elmo’s fire is a well-understood and predictable electrical event, ball lightning is unpredictable and not yet fully understood. Saint Elmo’s fire is always associated with solid objects, such as ship masts and airplane wings, while ball lightning’s main identifying feature is its independence.

Image credit – John Kain

Saint Elmo’s fire forms when there is a strong electrical field around the object (mast or wing, eg) which causes air molecules to become ionized, creating a visible plasma. It’s a relatively mild cousin of lightning. In a mechanism similar to aurora, the ionized nitrogen and oxygen molecules fluoresce with blue or violet light.

Image credit – Wesley Wong

Since Saint Elmo’s fire is a remarkable phenomenon it naturally has its attendant superstitions, most notably among sailors, who were most at risk during strong electrical storms. Some of them thought it was a bad omen, while others thought it was a sign that their saint (Elmo) was watching over them. We humans tend to think that these things are about us.

Saint Elmo’s fire is not dangerous. It won’t set things on fire and it won’t kill you if it touches you. If you’re lucky enough to see it, just enjoy it, although you should take the normal precautions for the associated thunderstorm.

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