October 6, 2011 Fireball over Southeastern USA
The American Meteor Society has so far received approximately 50 reports of a dazzling fireball over the southeastern USA including Florida, Georgia, Alabama and Mississippi. This event occurred near 8:40pm EDT (7:40pm CDT) Thursday evening October 6th. Of the reports received so far, green is the by far the most mentioned color. Vivid green fireballs are not unusual and in the case of slow meteors, such as this one, are usually caused by a particular element such as nickel or copper present in the meteor. The green color observed in swift fireballs are more likely caused by ionized oxygen caused by the passage of the meteor through the atmosphere. The average brightness reported by witnesses was near the light produced by a full moon.
A fireball is a meteor that is larger than normal. Most meteors are only the size of small pebbles. A meteor the size of a softball can produce light equivalent to the full moon for a short instant. The reason for this is the extreme velocity at which these objects strike the atmosphere. Even the slowest meteors are still traveling at 10 miles per SECOND, which is much faster than a speeding bullet. Fireballs occur every day over some parts of the Earth. It is rare though for an individual to see more than one or two per lifetime as they can also occur during the day or on a cloudy night. Observing during one of the major annual meteor showers can increase your chance of seeing another bright meteor.
Fireballs often appear much closer than they really are. The AMS receives countless reports that an object landed just over the hill when in fact it was several hundred miles away and was witnessed over several states. It is your perspective that makes meteors appear to strike the horizon when in fact they are still high in the atmosphere. This is much like a jetliner seen low in your sky. It appears low to you but for someone located many miles away in that direction, the jetliner is passing high overhead. Meteors become visible at approximately 50 miles above the Earth’s surface. Friction slows these objects down until they fall below the velocity necessary to produce light. At this point they still lie at least 5 miles high in the sky. They are invisible below this altitude and cannot be seen as they basically freefalling to the ground at 200mph. Very few meteors actually reach the ground as 99.99% completely disintegrate while still 10-20 miles up in the atmosphere.
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