More booming fireballs

The entire universe in blog form
March 30 2009 8:54 AM

More booming fireballs

Artist drawing of an asteroid entering Earth’s atmosphere
So it sounds like (haha) another interplanetary interloper took it upon itself to explode in our atmosphere, this time over the East coast of the US. There has been a streak (haha) of these lately, and I'm getting emails asking if that's unusual.

I do think it's a bit unusual, but not crazy or apocalyptic, or even mildly worrisome. There's a lot of junk out there in space, and it doesn't take a big piece of detritus to make a brilliant fireball. Something the size of a grapefruit will light up the night sky, and anything bigger than a beach ball will make a tremendous display even during the day. The thing to remember here is that these objects enter our atmosphere moving at least 11km/sec (7 miles/sec), and that translates into a huge amount of energy. They can have speeds up to ten times that much, too, meaning they have 100 times the energy (energy goes as velocity squared), and that energy is converted into heat and light.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Advertisement

As a rock slams into the air at those speeds, it compresses the air in front of it tremendously, which is why it gets hot (it's not friction per se; compressing a gas heats it up, and we're talking major compression here). This pressure also flattens the meteoroid, and it can break up into little pieces, each of which heat up, which then break up, heat up, and then BANG! They release all their energy in an explosion. If that happens low enough in the atmosphere (though still many miles high), you can actually hear the non-Earth-shattering (sorry Marvin) but still quite loud kaboom.

That's almost certainly what happened over Virginia yesterday. People say they saw a streak in the sky, indicating this was a meteor... though I have to tell you that specifics in eyewitness reports of meteors can be misleading. One person quoted in that article said it was definitely heading down, but in reality they can't know that. As a meteor streaks across the sky, it looks like it's heading down, toward the ground, but that's just perspective. If one were to skip off our air like a rock skipping on water (and that does happen), from the ground it might still look like it was heading down even though it might be moving up, away from the ground.

Another person said it was low, but again that is probably not correct. Most likely it was low in the sky, because the person was far away and the curving Earth made it look low, like the rising Moon at first is low to the Horizon. The object coming in was probably 20 km off the ground or higher. The only way you could know for sure it was low is if it passed in front of clouds (which would be hard to tell if the fireball were really bright) or in front of trees... which would mean you're in some small amount of trouble!

But what about the frequency of these things? There have been so many lately! Are we under attack?

No, I don't think so. I think it's a mix of coincidence -- there may be a few more than usual, but it's not like these things have published schedules; sometimes there are more and sometimes fewer -- together with people being more aware of them because they've been in the news lately. It's like buying a car and suddenly seeing it everywhere when you drive. We notice what we're primed to notice.

So I'm not worried about these. Instead, I think it's great! People are getting a first-hand taste of astronomy, and in a very exciting and memorable way! I hope people don't get scared by this, and instead enjoy it. The Universe is talking to us, and people are starting to listen.

TODAY IN SLATE

Frame Game

Hard Knocks

I was hit by a teacher in an East Texas public school. It taught me nothing.

Republicans Like Scott Walker Are Building Campaigns Around Problems That Don’t Exist

Why Greenland’s “Dark Snow” Should Worry You

If You’re Outraged by the NFL, Follow This Satirical Blowhard on Twitter

The Best Way to Organize Your Fridge

The World

Iran and the U.S. Are Allies

They just aren’t ready to admit it yet.

Sports Nut

Giving Up on Goodell

How the NFL lost the trust of its most loyal reporters.

Chief Justice John Roberts Says $1,000 Can’t Buy Influence in Congress. Looks Like He’s Wrong.

A No-Brainer Approach to Fighting Poverty: Better Birth Control

  News & Politics
The World
Sept. 16 2014 11:56 AM Iran and the U.S. Are Allies Against ISIS but Aren’t Ready to Admit It Yet
  Business
Business Insider
Sept. 16 2014 1:23 PM Germany Has Asked Google to Reveal Its Search Algorithm, but That's Not Going to Happen
  Life
The Eye
Sept. 16 2014 12:20 PM These Outdoor Cat Shelters Have More Style Than the Average Home
  Double X
The XX Factor
Sept. 15 2014 3:31 PM My Year As an Abortion Doula
  Slate Plus
Tv Club
Sept. 15 2014 11:38 AM The Slate Doctor Who Podcast: Episode 4  A spoiler-filled discussion of "Listen."
  Arts
Behold
Sept. 16 2014 12:59 PM Ethereal Views of Earth From Way Up High 
  Technology
Future Tense
Sept. 16 2014 12:33 PM Slate Exclusive: Why Greenland’s “Dark Snow” Should Worry You
  Health & Science
Bad Astronomy
Sept. 16 2014 7:30 AM A Galaxy of Tatooines
  Sports
Sports Nut
Sept. 15 2014 9:05 PM Giving Up on Goodell How the NFL lost the trust of its most loyal reporters.