Loud boom and bright fireball over California and Nevada on April 22

Image: Wikimedia Commons image of a bollide or fireball - a piece of space debris entering Earth's atmosphere and causing a particularly bright streak across the sky.

We’re getting reports and question from EarthSky’s Facebook and Twitter pages of a loud boom apparently heard in Nevada and California on Sunday morning (April 22, 2012). Some people in the two states reported seeing a fireball – a very bright “shooting star” – streak across the blue daylight sky at that same time. Many are saying that it was likely caused by a meteor, or piece of space debris entering our atmosphere, and there is no reason to think this is not the case.

Dan Ruby of the Fleischmann Planetarium at the University of Nevada, Reno, is reported widely as having said that the reports indicate the boom and fireball were caused by a meteor. If it was a meteor, it apparently broke up above Earth somewhere over the Sierra Nevadas. Astronomers in that area commonly would mount a search for a possible object on the ground – which would be called a meteorite – but I’ve heard nothing specific about such a search in this case.

Astronomers use the word bolide to describe an exceptionally bright fireball such as this one. The term bolide – which comes the Greek word bolis, meaning a missile or to flash – is particularly applicable when the object is so bright it can be seen in broad daylight, when the object explodes in the atmosphere and when it creates audible sounds. In other words, all of these phenomena are known to occur, and astronomers even have a word for it.

Among astronomers, it’s sometimes said you might witness one bolide, or very bright fireball, in your lifetime. So if you saw this one, this was yours! You might want to tell someone what you saw. Here’s a place to report your meteor sighting.

It so happens there is a meteor shower going on now, which peaked last night and might produce a sprinkling of meteors tonight. But it’s likely this bright fireball had nothing to do with the Lyrid meteor shower. Meteors in annual showers are known to come from icy comets, which, as they move through space, litter their orbits with debris. None of this debris ever reaches the ground because it starts out so small – like sand grains – and fragile (ice).

Sometimes in a meteor shower you will see a bright meteor! But I’ve never heard anyone speak of seeing a meteor in an annual meteor shower so bright that it might have been seen in daylight – or one that made a sound – or one that shook houses. If the object sighted today over California and Nevada was space debris, it was likely made of sturdier stuff than the icy grains that cause the Lyrid meteor shower.

Bottom line: Many in Nevada and California on the morning of April 22, 2012 saw a bright flash across the sky, and heard an audible boom, or explosion. Astronomers in the area say it was a meteor, or piece of space debris entering Earth’s atmosphere. Another word for this is bolide or fireball.

- EarthSky