Fireballs & Meteors

Meteor Streaking Through Night Sky

What is a meteor?

We’ve all seen them. They’re beautiful bright lights streaking across the heavens and disappearing as quickly as they appear. Sometimes if you’re lucky you get to witness and even rarer event like a fireball. Fireballs, bolides and meteors are the same thing, it’s all relative anyway.

Read my article titled What Is A Meteorite here for more info on the differences.

How big are meteors?
Most meteors you see are only as large as a grain of sand and burn up long before they get near the ground, usually at a fairly high altitude of around 50km-95km, the smaller ones burn up at much higher altitudes. Sometimes pieces that are as large as a basketball can enter our atmosphere and create a very bright fireball that lasts for a few seconds or more. Whether something this size could become a meteorite is arguable in the science community.  Most scientists believe that for a meteor to turn into a meteorite (survive impact with the Earth’s surface) a meteor has to be larger than a basketball. Even then they’re not entirely sure it would not burn up completely.

There are many factors to consider when trying to calculate whether a meteor could strike the ground. Size and mass, are the most obvious, but angle of entry, speed and even the material a meteor is made of all are determining factors on whether a meteor will reach the ground.

Leonid Meteor Shower

Leonid Meteor Shower

Meteor Showers
These beautiful displays of light are natures fireworks shows. They are caused when the Earth travels through comet debris during it orbit around the Sun.  Comets leave behind trails of debris that the Earth passes through. When this happens a meteor shower is born.

Meteor Videos: Check out the Cloudbait Observatory’s meteor videos from the Colorado Allsky Camera Network http://www.cloudbait.com/meteor/videos.php

Meteors & Fireballs Are Measured By Their Brightness
How bright a meteor fireball is is sometimes a good indicator of how large (not always) a meteor is. Meteor brightness is determined by a large number of factors and it is measured by a brightness magnitude scale. A meteors brightness can be affected by light pollution if you are in the city, or by fog, smog, or clouds. Distance from the observer doesn’t effect brightness so much as it does the perception of the brightness.

The farther you are away from an object the less detail you can see, therefore a basketball sized meteor that is 50 miles away on a clear night, will not be as bright to you if it were 75 miles away. If a meteor leaves a visible smoke trail that stay in the air for many seconds or even minutes, there’s a pretty good chance it hit the ground. Usually any smoke produced by meteors is not visible from the ground with your naked-eye.

Meteors are fast: Check out the American Meteor Societies Meteor Faqs page http://www.amsmeteors.org/faqm.html

Daylight Fireballs
If you see a meteor fireball during daylight hours consider yourself that much more lucky than someone viewing meteors at night. It’s easy to see a bright object flying across  the sky at night, but during daylight hours it takes a lot larger meteoroid to make a meteor large enough to be seen in daylight. There’s also more chance there will be a smoke trail and a greater possibility of impact.

Read about Fireballs: http://www.cloudbait.com/science/fireballs.html

Nasa: http://science.nasa.gov/headlines/y2005/03nov_taurids.htm

Fireballs Are Not Rare
As rare as they are to see it’s really not that uncommon at all for meteor fireballs to happen. I know this sounds counterintuitive but it’s not. Think about the fact that most people are asleep during nighttime hours. I would venture to say that 70% to 90% of all the fireballs that happen are never witnessed. Keep in mind seeing a meteor or fireball isn’t just about being awake and staring intently at the night sky. You most likely live in a relatively highly populated area and only have a view of a limited area of sky. If it’s night time where you are right now, I would be willing to bet that if you walked outside and stared at the sky for a few minutes without moving you would most likely see a meteor.

Light pollution plays a big factor in being able to spot meteors. If you live in the suburbs you have less light pollution than say if you live in downtown New York city. The glare from the lights around you effect your ability to even see the sky much less see a brief streak of light shooting across the sky for a split second. If you live in the country your more likely to see a shooting star. Pick any night, pick any location on the planet and if you scan at the skies long enough you’re guaranteed to see a meteor. How big it will be is anyone’s guess, but you will not be disappointed.

Another factor that play a large part in human beings actually witnessing fireballs is that we spend most of our time indoors. Factor in the time spent sleeping (when meteors are most visible), working, and in your car. There’s not much time left in the day when you might see a meteor. Logic would have it that if you spent more of your time outdoors that you would see more meteors and it’s absolutely true. It’s easy to see why meteors really aren’t that rare at all.

Impact Events
For a meteor to reach the ground many things have to happen and conditions have to be perfect or the meteor will not survive entry or impact with the ground. If a meteoroid is large enough it will reach the ground. How large that is depends on the mass, angle of entry into the atmosphere, material the meteoroid is made of and the meteoroid speed as it hits the outer reaches of our atmospheric shield. The faster a meteor is moving the more resistance, this friction heats the outer surface of the stone (or iron in the case of an iron meteoroid) and causes it to start to burn up. The greater the angle of decent the faster it will be slowed by the resistance on the air, producing more friction and heat. A small meteor won’t last long during these conditions and usually burns up quickly.

Larger iron meteoroids or even large stone type meteoroids have a better chance of making it to the ground if they come in at a relatively low angle and they are of large enough size. If they come in too steep they’ll either burn up fast and fragment into thousands of tiny pieces, or explode. Large fireballs can even explode on impact with enough force to devastate the land forming huge craters more than 500 feet deep such as Meteor Crater in Arizona.

Meteor Crater: The worlds most famous meteorite crater

This is perhaps the best preserved meteorite crater on the face of the planet and a perfect example of everything going right. The meteor was able to punch through the atmosphere, survive entry, and impact the ground. This is perhaps the best example of a meteorite impact. Obviously something of this size is extremely rare, and even this one happened some 50,000 year ago.

But If you think about this, meteors are happening right now somewhere on our planet. We are bombarded with millions of meteoroids every single day, and millions of tons of galactic space debris per year. Estimates say there are between 1-10 meteorites per square mile all over the planet.

"On any dark night, an observer can expect to see half a dozen
meteors, but the total number that might be seen in any 24 hour period
from all points on the earth reaches an unbelievable figure of
approximately 90 million. " SOURCE: http://answers.google.com/answers/threadview?id=192044

There’s more meteorites out there than we can possibly imagine.

Have you seen a fireball? Report A Fireball