A bolide is a meteor that is brighter than the planet Venus (i.e. a fireball), and which explodes or breaks up (usually accompanied by a sonic boom) before reaching the ground. There are of order 5,000 bolides per year fall to Earth but very few of these are actually observed. This is because:

• they fall over the sparcely populated areas that make up the majority of the Earth (including oceans)
• they fall during the day and are masked by the brightness of the Sun
• they fall during the night when few people are awake to observe them.