What Causes the Blue or Violet Glow of St. Elmo Fire?

💡 The Answer

• The glow comes from excited nitrogen and oxygen molecules in the air.
• When electrons collide with air molecules, they emit photons at specific wavelengths.
• The violet-blue color is due to the strong emission lines of molecular nitrogen.
• Different gas mixtures can shift the color slightly, but blue dominates near sea level.