Astronomy Jargon 101: Bolide

In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll be struck by today’s topic: bolide!

It’s a bird! It’s a plane! It’s a…bolide?

The word “bolide” has two main definitions, and even then it’s never used in a consistent way. The International Astronomical Union, for example, hasn’t established a definition for the term. So if you encounter the word out in the wild, you’re just going to have to use context to figure out what the author meant.

Generally, in astronomy a bolide refers to any exceptionally bright meteor. But different people have different definitions of what “exceptionally” means. In some uses, it refers to any meteor that reaches a brightness of at least two full Moons. In other uses, it refers to any fireball, which is a meteor large enough to visibly emit flames (really super-heated bits of rock) as it crashes through our atmosphere. Further still, sometimes the word only refers to a meteor that completely explodes in our atmosphere without ever hitting the ground.

Geologists, on the other hand, have a completely different sense of the word. They use it to describe any impactor, which is any rock large enough to leave a crater on the ground. Still then there is disagreement. Some geologists, like the Woods Hole Coastal and Marine Science Center, use the word to refer to any impactor of unknown origin. It could be a comet, a stony asteroid, or a metallic asteroid, but until that distinction is made, it’s simply a bolide.

All that said, whatever the definition, bolides generally refer to some version of large rocks hitting the Earth.