St. Elmo's Fire: What is the Mystery Behind the Natural Phenomenon?

What is St. Elmo's Fire Phenomenon?
Reported by scholars and sailors alike, St. Elmo's Fire, was for many years shrouded in mystery. This Buzzle post will tell you about this arcane phenomenon, and the take that scientists have on it.
Did You Know?
St. Elmo's Fire is named after St. Erasmus, the Patron Saint of Sailors, and the phenomenon is regarded as a sign from him.
St. Elmo's Fire is a bluish glow seen near tall, pointed objects, and might be accompanied by a hissing or cracking sound. Some people have reported it as spherical, while many witnesses claim it is more like flames. Its color also varies from bluish-white to purple-tinged. It is mostly associated with the sea - sailors, specially from the Mediterranean region, often reported flames emanating from the masts, usually accompanying a thunderstorm. As the phenomenon was observed to be the most intense after a violent storm, and the flames never damaged the masts, many sailors regarded it as a sign from St. Erasmus.

Historically, the phenomenon is widely documented by luminaries like Charles Darwin, Julius Caesar, and Pliny the Elder, to sailors and soldiers. It is also not restricted to a particular area, and has been sited by people from all over the world, including the Japanese, Russian, Welsh, and Filipinos. Santelmo, a mythical creature from Philippines is also based on St. Elmo's Fire, while the Greeks associate it with fire. The Chinese though, consider it as an omen from Tianfei, the Goddess of Sailors and Seafarers.

It is not just a historical phenomenon though; St. Elmo's Fire has been reported even recently on objects, such as electrical poles, aircraft wings, church spires, pipes, propellers, and lightning rods. A few people have also claimed to see it on cattle horns and blades of glass. The sightings increase when the atmosphere is highly charged, such as in the vicinity of tornadoes.
Scientists' Take on St. Elmo's Fire
Scientifically, the phenomenon is known as a corona discharge. It is a type of electrical discharge caused by a difference in the electrical charges of the air and ground. During certain atmospheric conditions, such as in a storm, the air becomes ionized and can conduct electricity. The air, during a thunderstorm, can get charged up to 30,000 volts per centimeter of space. But a grounded object, such as the masts of a ship or church spires have a similar electric potential to that of the ground (around 0 volts). This dramatic difference in electric potential can cause electrons to be pulled away from atoms in separate clusters. This process is what causes the air to glow and emit a hissing or cracking sound.

It occurs on pointed objects because they have less surface area to discharge, and hence, will discharge at a lower voltage level. The color of the glow will depend on the gas―oxygen emitting a blue glow and nitrogen a purplish glow.

Nikola Tesla, the inventor of the Tesla coil, developed a plasma ball employing the same principle as St. Elmo's Fire. Though developed for decoding the properties of electricity, it is mostly used as a novelty device in parties.
Similar Phenomena in Nature
Many other phenomena in nature arise in similar conditions, and are similar to St. Elmo's Fire. Here are a few of them.
Lightning
Lightning strikes
Lightning has many similarities to St. Elmo's Fire. It occurs during storms due to electrical discharge, and is attracted to tall, pointed objects. But, it is different from the St. Elmo's Fire, as it is a quick, fast blast of electrical charge, whereas St. Elmo's Fire is a continuous glow, lasting for a few minutes.
Ball Lightning
Ball lightning is a term given to luminescent, circular objects, which are said to be capable of exploding and moving through walls. They are also associated with storms, but are very unpredictable and infrequent, which also means that they are not scientifically proven or investigated till date.
Aurora borealis and Aurora australis
Aurora borealis and Aurora australis
This beautiful phenomenon is observed in the auroral zone as a band of luminous, colorful light. It is caused due to the interaction between charged electrons from solar winds and the Earth's atmosphere.
Transient Luminous Event
This is a term used for bright flashes in the upper atmosphere, which occur above the storm clouds after strong lightning strokes, and soar upwards. They come in many forms, and bear whimsical names like sprites, jets, elves, etc.
To summarize, St. Elmo's Fire is a blue or purple glow which can resemble a ball or flames, seen in conjunction with storms. Requiring set atmospheric conditions to occur, it is pretty rare in nature, and was given divine interpretation in ancient times.