by neufer » Sat Aug 18, 2018 6:00 pm
Chris Peterson wrote: ↑Fri Aug 17, 2018 6:17 pm
clr wrote: ↑Fri Aug 17, 2018 4:52 pm
What did the fireball crash into? Did it do any damage?
It was reduced to dust and a cloud of atoms while still 100 km above the ground.
- 100 km above the ground would be reasonable for most shooting stars;
but fireballs should make it a little further down:
https://www.amsmeteors.org/fireballs/faqf/ wrote:
1. What is a fireball? What is the difference between a fireball and a bolide?
- A fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation.
6. Can a fireball create a sound? Will the sound occur right away, as you watch the fireball, or is their some delay?
- If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km, and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon. Because sound travels quite slowly, at only about 20 km per minute, it will generally be 1.5 to 4 minutes after the visual explosion before any sonic boom can be heard.
7. How bright does a meteor have to be before there is a chance of it reaching the ground as a meteorite?
- Generally speaking, a fireball must be greater than about magnitude -8 to -10 in order to potentially produce a meteorite fall. Two important additional requirements are that (1) the parent meteoroid must be of asteroidal origin, composed of sufficiently sturdy material for the trip through the atmosphere, and (2) the meteoroid must enter the atmosphere as a relatively slow meteor.
Meteoroids of asteroid origin make up only a small percentage (about 5%) of the overall meteoroid population, which is primarily cometary in nature.
Photographic fireball studies have indicated that a fireball must usually still be generating visible light below the 20 km altitude level in order to have a good probability of producing a meteorite fall. Very bright meteors of magnitude -15 or better have been studied which produced no potential meteorites, especially those having a cometary origin.
8. Can a meteorite dropping fireball be observed all the way to impact with the ground?
- No. At some point, usually between 15 to 20 km altitude, the meteoroid remnants will decelerate to the point that the ablation process stops, and visible light is no longer generated. This occurs at a speed of about 2-4 km/sec.
From that point onward, the stones will rapidly decelerate further until they are falling at their terminal velocity, which will generally be somewhere between 0.1 and 0.2 km/sec (200 mph to 400 mph). Moving at these rapid speeds, the meteorite will be essentially invisible during this final “dark flight” portion of their fall.>>
[quote="Chris Peterson" post_id=285081 time=1534529826 user_id=117706]
[quote=clr post_id=285075 time=1534524767 user_id=144433]
What did the fireball crash into? Did it do any damage?[/quote]
It was reduced to dust and a cloud of atoms while still 100 km above the ground.[/quote]
[list]100 km above the ground would be reasonable for most [i][color=#0000FF]shooting stars[/color][/i];
but [b][color=#FF0000]fireballs[/color][/b] should make it a little further down:[/list]
[quote=" https://www.amsmeteors.org/fireballs/faqf/"]
1. What is a fireball? What is the difference between a fireball and a bolide?
[list]A fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation.[/list]
6. Can a fireball create a sound? Will the sound occur right away, as you watch the fireball, or is their some delay?
[list]If a very bright fireball, usually greater than magnitude -8, penetrates to the stratosphere, below an altitude of about 50 km, and explodes as a bolide, there is a chance that sonic booms may be heard on the ground below. This is more likely if the bolide occurs at an altitude angle of about 45 degrees or so for the observer, and is less likely if the bolide occurs overhead (although still possible) or near the horizon. Because sound travels quite slowly, at only about 20 km per minute, it will generally be 1.5 to 4 minutes after the visual explosion before any sonic boom can be heard.[/list]
7. How bright does a meteor have to be before there is a chance of it reaching the ground as a meteorite?
[list]Generally speaking, a fireball must be greater than about magnitude -8 to -10 in order to potentially produce a meteorite fall. Two important additional requirements are that (1) the parent meteoroid must be of asteroidal origin, composed of sufficiently sturdy material for the trip through the atmosphere, and (2) the meteoroid must enter the atmosphere as a relatively slow meteor.
Meteoroids of asteroid origin make up only a small percentage (about 5%) of the overall meteoroid population, which is primarily cometary in nature.
Photographic fireball studies have indicated that a fireball must usually still be generating visible light below the 20 km altitude level in order to have a good probability of producing a meteorite fall. Very bright meteors of magnitude -15 or better have been studied which produced no potential meteorites, especially those having a cometary origin.[/list]
8. Can a meteorite dropping fireball be observed all the way to impact with the ground?
[list]No. At some point, usually between 15 to 20 km altitude, the meteoroid remnants will decelerate to the point that the ablation process stops, and visible light is no longer generated. This occurs at a speed of about 2-4 km/sec.
From that point onward, the stones will rapidly decelerate further until they are falling at their terminal velocity, which will generally be somewhere between 0.1 and 0.2 km/sec (200 mph to 400 mph). Moving at these rapid speeds, the meteorite will be essentially invisible during this final “dark flight” portion of their fall.>>[/list][/quote]