Ball lightning and other rare atmospheric lights

Not every unexplained light in the sky is a craft, a satellite or a planet. Some come from the atmosphere itself, and a few of them are rare enough that scientists are still arguing about how they work. This file sorts them into three groups: understood, partly understood and still puzzling.

Ball lightning: the open question

What people report

Ball lightning reports go back centuries. Witnesses describe a glowing sphere, often during or just after a thunderstorm, that floats or drifts near the ground, sometimes enters buildings, and lasts from a moment to several seconds before fading or vanishing with a pop. Reported colors range from white and yellow to red and blue.

One of the most cited historical accounts is the Great Thunderstorm of 1638 at Widecombe-in-the-Moor in Devon, England, when a storm struck a church during a service and witnesses described a ball of fire. Accounts like this are hard to interpret centuries later, but they show the phenomenon is not new.

The first scientific recording

For a long time, ball lightning existed only in eyewitness accounts. That changed in July 2012, when a team of Chinese researchers studying ordinary lightning on the Qinghai plateau happened to record a ball of light with their instruments, including a spectrograph. Their findings, published in Physical Review Letters in 2014, showed the ball's light contained signatures of silicon, iron and calcium, elements found in soil.

That result fits one of the leading hypotheses: that lightning striking the ground vaporizes soil, and the resulting material glows as it oxidizes in the air.

Why it's still unexplained

The soil-vapor idea is one of several:

Hypothesis	The idea	The difficulty
Vaporized soil	Lightning turns silicon in soil into glowing vapor	Doesn't easily explain reports of ball lightning indoors or inside aircraft
Microwave or plasma models	Energy trapped in a bubble of plasma	Hard to test outside the lab
Magnetic effects on the brain	Strong magnetic fields from lightning trigger visual sensations	Would explain some reports, not recorded instrument data

One observation on instruments is a breakthrough, but it is not enough to say which idea is right, or whether different "ball lightning" reports describe different things. We mark this file Unexplained for that reason.

Understood: lights we can explain

St. Elmo's fire

A blue or violet glow on pointed objects such as ship masts, aircraft wingtips or church spires during stormy weather. It is a corona discharge: a strong electric field ionizes the air around a sharp point. Sailors have reported it for centuries, and pilots still see it.

Sprites, jets and elves

Above large thunderstorms, brief flashes can extend high into the upper atmosphere.

• Sprites are red, often jellyfish-shaped, and last a fraction of a second. They were first captured on camera in 1989 by researchers at the University of Minnesota, after decades of pilots' reports that had often been doubted.
• Blue jets shoot upward from the tops of storm clouds.
• Elves are expanding rings of faint light at the edge of space.

Sprites are a good reminder that "unexplained" and "imaginary" are different. Pilots reported them long before cameras confirmed them.

Noctilucent clouds

Thin, electric-blue clouds that glow after sunset on summer nights at high latitudes. They are very high and catch sunlight long after the ground is dark.

Partly understood: local light phenomena

Some places have reports of recurring lights.

The Hessdalen lights, Norway. Residents of the Hessdalen valley have reported unusual lights since at least the early 1980s. A research effort, Project Hessdalen, began in 1983 and later set up automated monitoring. Researchers have proposed several mechanisms, but no single explanation is settled.

The Marfa lights, Texas. Lights reported near Marfa, in West Texas, have attracted visitors for generations. A 2004 study by students at the University of Texas at Dallas concluded that the lights they recorded were most likely vehicle headlights on a nearby highway. Others argue some historical reports predate heavy traffic.

Earthquake lights. Glows and flashes have been reported before or during some earthquakes. Scientists have proposed electrical effects in stressed rock, but the phenomenon is rare and difficult to study.

How to tell a rare light from a craft

• Weather context. Ball lightning, St. Elmo's fire and sprites are tied to thunderstorms. If a storm was nearby, note how close.
• Duration. Sprites last a fraction of a second. Ball lightning lasts seconds. Anything that persists for many minutes is less likely to be either.
• Place. Some valleys and plains have long histories of lights. Look them up.

Safety first

If you see something unusual during a thunderstorm, stay indoors. Lightning is the hazard; observing can be done from a window. Make notes afterward.

What remains unexplained

Ball lightning remains one of the most frequently reported natural phenomena that physics has not fully explained. Some UFO reports may well be ball lightning; some ball lightning reports may be something else. Careful notes on weather, timing and appearance are what will eventually sort them.