Witnesses across much of Western Australia reported seeing a bright fireball meteor at about 1.00 am local time on Monday 15 June 2020. The meteor was described as being greenish in colour, which probably indicates a high magnesium content, and slow moving, which suggests a meteor moving at a shallow angle (i.e. close to horizontal) high in the atmosphere. 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 may be the result of
man-made space-junk burning up
on re-entry.
Fireball meteor over Western Australia on 15 June 2020. Perth Observatory.
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).
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 Australia you can report it to the Desert Fireball Network here.
See also...
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