So is it a fireball or a bolide?

12 06 2008

If you look at my personal info it says that my interests include meteors. However, I haven’t written anything about meteors yet. I’m rectifying that now.

Do you know the difference between a fireball and a bolide? Well you’re not alone! I’m on the meteorobs listserv, which can be a pretty technical group at times and therefore shouldn’t be subscribed to if you just want to say, “I saw a pretty one.” Although, we *do* like hearing about the pretty ones. Heh. Over the last couple of days we’ve had a pretty vigorous discussion about the definition of these two terms.

First off, the only group who can define any astronomical term is the International Astronomical Union (IAU). Those are the folks who defined “planet” some time ago and put Pluto in its place. They also get to name asteroids and craters and moons and so on. They are also the only group who can name stars…and NO, they cannot be bought!

The whole reason they had to define what makes a planet and what makes a comet or whatever is because there was no formal definition for planet. Everyone just kind of agreed that Pluto was a planet and Ceres wasn’t, for whatever reason. The definition was vague. Much the same as the definition for meteors.

Meteoroid — any natural body in space smaller than an asteroid.

Meteor — extraterrestrial debris moving through our atmosphere.

Fireball — A meteor brighter than any of the planets.

Bolide — Well, we’re not really sure since the IAU has never bothered to define it.

Got that? Are you sure? Rather vague isn’t it…? So we in the meteor community have made some definitions on our own that many of us use yet seems to tick off some of the members who think we should stick to the IAU’s definitions. And by “definitions” I’m assuming their dictionary happens to include “Birds — flying things smaller than planes and bigger than insects” and “VIPs — Firemen, math teachers, and so on in that fashion.” If the IAU were to tackle the life sciences I wonder if they would file bananas under “Yellow, things that are” ? Seriously. This is what happens when 400+ people vote on a single definition.

But the IAU might be considering nomenclature that would allow “meteors” to define all four terms. We’ll see.

So here are the definitions I use. Albeit, I use these because I was led by the greater community, but these new arguments aside I just like these definitions. Nothing official or formal, so don’t quote me. :o)

1. Meteoroid. I *never* use the term meteoroid.

2. Meteor. I say meteor for all objects that could be considered fragments of asteroids or comets. If a comet leaves a trail of debris, I call that debris a meteor stream.

3. Fireball. I’m going with everyone else here and saying that a fireball must be brighter than Venus (about magnitude -4).

4. Bolide. Here’s where I’ll break off and make my own definition. To me a meteor gets raised to the bolide class by being as bright as a 1st quarter moon. This should be bright enough to leave crisp shadows and easily bright enough to read a newspaper. Many classify bolides as having to explode or even be heard. Since I’m getting the privilege of making this up as I go I would say that these events are typical, but not necessary for the classification.

YCSentinel, one of the group, suggested we also come up with two terms to define meteors that fragment slowly and those that fragment explosively. Any suggestions? Might as well have a say! Or at least pretend like you do.

So there’s your science lesson for the day. Hopefully, even some of you astronomy elitists will feel contrite for your inexplicable ability to talk for thousands of years without actually defining what you’re talking about.

As I feel I must, if you do see a fireball take a note of everything you think you can remember. Then please fill out the treasured Fireball Report ASAP. The info is used by people who really want to know.




5 responses

13 06 2008
Nick Jones

Slow fragmentation: glacial. even though it implies that there’s ice, the people who would be using it (I hope) would know better
Explosive fragmentation:Napalm/ Agent Orange or the like. It might be in poor taste, and the orange might be a misnomer as to the color of the explosions but it makes sense, to me at least.

also, Why does a moon rock taste better than an Earth rock?
Because its a little METEOR!

13 06 2008
Terry Johnson

Wow. Just wow.
Worst. Joke. Evah.

13 06 2008
Nick Jones

Address all complaints to the Monsanto Corporation.

25 09 2008
MIke Cox

On Thursday, Setember 25, 2008, at 6:25 EDT, in Cleveland, Ohio, I saw a fireball which appeared to be traveling from northeast to southeast. The color was a brilliant blue-white, and the object appeared to fracture into two parts as I watched. As it disappered behind the tree line, it was still glowing brightly. My impression of the brightness was definitely brighter than Venus, but less than a quarter moon.

25 09 2008
Terry Johnson

I hope you filled out a fireball report with the IMO. The link was listed at the bottom of the post. Thank you.

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