Bow shocks form as particles pile up in front of an object moving through them, the video explains. These could be water molecules in front of a boat, dust in front of a star, or ions in front of a magnetic field. The particles heat up as they compress, forming teardrop-shaped shock waves with the tail pointing downstream.
"Studying stellar bow shocks can reveal the secret motions of the underlying stars, telling us how fast they're moving, which way, and what they're moving through," the video explains. Likewise, investigating the Earth’s magnetic bow shock can help scientists better understand the solar wind.
Along with explaining this physical phenomenon, the NASA video includes gorgeous images of the cosmic shock waves.