What visible electric discharge on the mast of a ship or the wing of an airplane during an electrical storm is named after the fourth-century patron saint of sailors, and is also the title of a 1985 movie starring Robe Lowe and Demi Moore?

The phenomenon you're thinking of, a luminous electrical discharge sometimes seen on pointed objects like ship masts or airplane wings during a thunderstorm, is known as Saint Elmo's Fire. This intriguing natural occurrence is a form of plasma, created when the electric field surrounding the object becomes strong enough to ionize the air molecules, causing them to glow. It's often accompanied by a crackling sound and can appear as a blue or violet glow, or even a brush-like discharge.

Sailors throughout history regarded Saint Elmo's Fire with a mix of awe and superstition. While it indicated high electrical activity, it was often seen as a good omen, suggesting that their patron saint, Saint Elmo, was watching over them. Saint Elmo, also known as Erasmus of Formia, was an early Christian martyr and bishop who became revered as the patron saint of sailors. Legends say that he continued preaching even after his intestines were wound out on a windlass, making him a symbol of perseverance and protection during dangerous voyages.

Beyond its scientific and historical significance, Saint Elmo's Fire also captured popular imagination in the 20th century. It famously lent its name to a 1985 American coming-of-age drama film, "St. Elmo's Fire," which starred a group of young, successful actors often referred to as the "Brat Pack," including Rob Lowe and Demi Moore. The movie explored the lives and relationships of recent college graduates navigating post-collegiate life, further cementing the evocative name in popular culture.