What is a fireball?
A fireball is an exceptionally bright meteor, usually defined as brighter than the planet Venus. It is caused by a larger-than-usual piece of space rock entering the atmosphere.
Most shooting stars are made by specks no bigger than a grain of sand, which burn up as brief streaks. A fireball is the same phenomenon on a grander scale: a meteor so bright it can light up the landscape, cast shadows, or be seen in daylight. Astronomers usually define it as any meteor brighter than magnitude −4, roughly the brilliance of Venus, the brightest planet. The word bolide is often used for a particularly bright fireball, especially one that explodes or fragments.
A fireball means a larger object, perhaps the size of a pebble, a football or bigger. It typically glows for several seconds, longer than an ordinary meteor, and may change colour as different elements are heated: greens and blues are common, with orange or red near the end. Many break into fragments that trail behind like sparks, and some leave a glowing or smoky train hanging in the sky for seconds or minutes.
Most fireballs are not dangerous and drop nothing. Small or fragile bodies, especially those from comets, are destroyed completely. A fireball that ends low in the atmosphere, roughly below 30 km, and is still bright when it fades is the kind that may have left meteorites on the ground. Dense, slow-moving rocky or metallic bodies are the best candidates. The Winchcombe fireball over England in February 2021 was one such event and was caught on many cameras.
Fireballs can appear on any night, but they are a little more common during some meteor showers, such as the Taurids in autumn and the Perseids in August. If you see one, note the time, direction and how long it lasted, and report it to a national meteor or fireball network so scientists can work out its path.