The American Meteor Society has
received reports of a bright fireball meteor being seen over northern Alabama slightly after 0.15 am local time on
Wednesday 7 March 2018 (slightly after 5.15 am on Friday 17 August GMT). The
event was witnessed from Kentucky, North Carolina, South Carolina and Georgia, though most of the reports came from Alabama. A fireball
is defined
as a meteor
(shooting star) brighter than the
planet Venus. These are typically caused by pieces of rock burning up in
the atmosphere, but can be the result of man-made space-junk burning up
on re-entry. The Object has been calculated to have been moving from
southeast to northwest
over the northern part of the state, and appears to have broken up about 30 km above the community of Grove Oak.
The 17 August 2018 fireball imaged from a meteor observing camera in the region. NASA Meteor Watch.
Objects
of this size probably enter the Earth's atmosphere several times a
year, though unless they do so over populated areas they are unlikely to
be noticed. They are officially described as fireballs if they produce a
light brighter than the planet Venus. The brightness of a meteor is caused by friction with
the Earth's atmosphere, which is typically far greater than that caused
by simple falling, due to the initial trajectory of the object. Such
objects typically eventually explode in an airburst called by the
friction, causing them to vanish as an luminous object. However this is
not the end of the story as such explosions result in the production of a
number of smaller objects, which fall to the ground under the influence
of gravity (which does not cause the luminescence associated with
friction-induced heating).
Map
showing areas where sightings of the meteor were reported, and the
route of the object (blue arrow). American Meteor Society.
These 'dark objects' do not continue along the path
of the original bolide, but neither do they fall directly to the ground,
but rather follow a course determined by the atmospheric currents
(winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark
objects derived from meteors using data from weather monitoring services.
Witness reports can help astronomers to understand these events. If you
witness a fireball-type meteor over the UK you can report it to the American Meteor Society here.
See Also...
