Written by Kelly Herbst, Astronomy Curator for the Virginia Living Museum. Updated every two weeks, more or less.

Wednesday, March 27, 2013

Fast Times Over East Coast Skies

Did you see it?

Last Friday, I got a phone call around 9pm from one of our local television stations.  They were getting lots of calls about some kind of meteor or something being seen in sky from all over the area.  Did I know anything about it?

Sadly, I'd been in my house all evening and missed the show.  But a quick internet search (oh whatever did we do before the internet!?) told me all I needed to know...people from Canada to Florida had seen a fireball...a dramatic meteor that lit up the skies all over the East Coast of the United States.

Two images of the East Coast Fireball from an astronomy camera in New York.  Images by Carl Fuller.

Since big sky rocks have been much in the news lately, I thought I'd use this week's post to define a few terms that have been tossed around of late.  I've got five of them for you, and once you've learned the differences between them, you too might get a phone call from a tv station, asking you for your expert opinion!  Okay, maybe not...but at least you'll know what these folks are talking about...and when they slip up and use the wrong word.

Let's start with the most common word: meteor.  A meteor is the streak of light created when a piece of material (usually rock and/or metal, but sometimes ice as well) comes in contact with the Earth's atmosphere.  The rock rubs against air molecules as it moves, generating lots of heat via friction.  This heat makes the air the rock passed through glow - and that's the streak of light we call a meteor.  The rock itself is not the meteor - in fact, we call it a meteoroid.

A meteorite is a piece of rock or metal that has traveled through the Earth's atmosphere from space and survived creating a meteor.  It crashes into the ground (sometimes creating a crater - a hole in the ground where it hit), and once the rock is on the ground, we call it a meteorite.  Finding a meteorite after seeing the meteor is very rare.  The vast distances involved often make it very difficult to judge where such an object may have landed.  There were early reports of the meteor on Friday having hit somewhere on the border between Maryland and Virginia, but this is extremely unlikely.  NASA has since analyzed the reported sightings of the meteor and they believe that any material that survived the passage likely fell into the Atlantic Ocean.

A meteorite nicknamed "Black Beauty."  The rock is believed to be from Mars, and landed in North Africa here on Earth.  The rock has been cut open and polished to reveal the inner structure.  Image courtesy NASA.

Okay, that's the big three.  But there are two more terms we need to come to grips with, and they've been tossed around a lot in recent days.  Some meteors are very bright - like the one that lit up the skies last Friday.  When a meteor is brighter than any of the planets (that is, brighter than Venus, the brightest object in the sky after the Sun and Moon), we call it a fireball.  Fireballs can be quite spectacular - often they show colors, since a chunk of material big enough to generate that much heat is going to be cooking lots of different materials - both on itself and in the air.  Such superheating can cause different molecules to glow with different colors of light.  Many people saw different colors in the trail of the meteor on Friday - and indeed, it was bright enough to qualify as a fireball.

Finally, the word bolide often comes into play when we talk about really bright meteors.  A bolide is a fireball that ends with an explosion - the rock becomes so superheated it detonates and explodes.  Such explosions are often accompanied by noises.  While several people reported seeing the Friday meteor fragmenting (bits and pieces may have been coming off), and some did report hearing noises accompanying the meteor's passage, the rock did not explode.  So it was not a bolide.  The recent fireball over the Siberian region of Chelyabinsk - that was indeed a bolide.  And a big one too.

So there you have it - you are now ready to speak with confidence about any shooting stars you might happen to see in the evening sky.  Did you see the one last Friday?  Leave a comment and tell me about it!

One more thing - I hope you got to see Comet PanSTARRS.  One of our wonderful volunteers did - and here's the photo to provide it!  Thanks to Mark Jablow for letting me use his beautiful picture.

A beautiful image of Comet PanSTARRS just after sunset.  Image by Mark Jablow.

Spring Break is coming for our area - so enjoy!  The museum will be open every day and we've got a full schedule of planetarium shows to keep the kids busy - hope to see you here next week!
Until then,
Carpe noctem!

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