Bolide

As a bolide (s) or fireball a particularly bright meteor is called. Meteors are caused by the penetration of meteoroids in the Earth's atmosphere.

Distinction between

The term is usually used for meteors whose apparent brightness is greater than that of the brightest planets, Venus, ie greater than -4 mag. Light Weaker events are referred to as shooting stars. Occasionally, for a particularly bright event that is brighter than about -17 likes, or about 100 times brighter than the full moon, the name Super Bolide used. However, both boundaries are not sharp.

Event

While the luminous trail ( ionization of the air ) of most meteors ends already above 60 kilometers altitude, larger meteoroids can achieve lower final heights ( about 20 miles) at a slower entry ( below about 25 km / s) and stronger material. Then, increasing the likelihood that material falls as a meteorite on the surface. A meteorite fall is also in very bright fireballs not the rule.

Brightness evolution

The brightness of a meteor is determined by its mass, but even more from his entry speed into the Earth's atmosphere. The ionization of the atmosphere and the ablation of the intruding material per unit time to determine the brightness of the meteor. If suddenly a lot of material per second removed from the meteoroid, the meteor is indeed much brighter, but the intruder loses now much faster mass. For this reason, it often happens that meteoroids made ​​of soft, rather loose material ( about 2 s) rise (eg cometary objects ) in a very short time in a spectacular fireball and other, more solid materials (eg, stony objects ) in a much longer flight phase ( about 6 s ) consumed in the form of a less spectacular fireball, although both meteoroids otherwise had the same initial conditions ( inlet velocity and mass ). The less ablation shows the penetrating projectile, the greater the chance for a rest mass that can reach the ground.

Fragmentation

Objects with large initial mass will penetrate deep into the Earth's atmosphere (eg, 20 km). As the air density increases strongly towards the surface, and the action on the object is always intense. The meteoroid is at the same time getting smaller and weaker. There is a situation in which the strength of the atmosphere for the penetrating material to be too large. A fraction of inhomogeneities in the material is likely and the body fragmented. It comes as a rule to a outburst. Even a regular meteor can be a fireball or bolide for at this moment.

With the fragmentation and the suddenly increased surface it also comes at a much higher ablation rate, which determines the light production and thus those light eruption can arise. In this flow, the highly compressed gas (or plasma) now also between the newly formed fragments and learn from doing a lot less resistance than just before, as the object still existed as a whole. The compressed gas can abruptly expand further and drives the resulting meteorite pieces apart. If these fragments survive the further fall, there will be a meteor shower.

Meteorite fall ( perception)

The perception of a meteorite fall begins with suitable weather conditions with a spectacular light phenomenon. During the day or in cloudy weather we see nothing in the rule. After such a fireball or bolide event can a short time later to the perception of a sound phenomenon ( sonic boom ) will come when the meteorite with multiple speed of sound crashes through the increasingly dense atmosphere. Depending on the position of the observer to the flight path and, depending on the course, there may be a short bang, but it can also come to an on and off again decongestant sound intensity. Depending on the distance of the observer to the flight path, size and speed of the meteorite, the thunder quickly follow and be very loud or arrive until several minutes later, a dull rumble of thunder at the observation site. In too great a distance to the trajectory or inappropriate acoustic conditions ( noise, noise control ) the perception of the sound event can also fail.

Noted events

Pictures of Bolide

136916
de