Originally posted by fiftyfifty
Never before as I'm aware have they produced so many large objects and so far in advance. Really don't think that they are related
Yep, they are not
11. Is there a chance of a meteor from a meteor shower or storm reaching the ground as a meteorite, and is it dangerous to observe meteor
The meteoroids which make up a meteor shower or storm are very fragile in nature, and are composed of a somewhat “fluffy” composite of
material from which all volatile material has escaped, due to many trips near the sun. This material readily vaporizes in the upper atmosphere,
and is given the descriptive name of “friable” material. While quite spectacular to watch, a meteor storm presents no real danger to the viewer,
who is protected by miles of atmosphere.
Source: The American Meteor Society Meteor Shower FAQs
I can also prove
that an Orionid could not have caused this event:
The radiant must be above the observer's local horizon in order for meteors from that particular shower to be visible.
In the case of the Orionid radiant
, at the time of the event in question, the
radiant would have been over 15 degrees below the horizon
, as you can see in the screen shot below of my planetarium software that was set to
16:15 BST on the 18th. The thicker white horizontal line represents the horizon, and I've indicated the approximate position of the radiant with a
Here's an illustration of the position of the Orionid radiant
In fact, the quote from wikipedia is slightly misleading as meteors from a meteor shower who's radiant is below the horizon can be seen
not when it is below about15 degrees. Meteors seen belonging to a meteor shower who's radiant is below the horizon are known as "earth grazers", and
they can be very impressive to see. However, due to the angle involved, an earth grazer from a radiant below the horizon, would always be traveling
upwards in relation to a person observing it
. So it would be physically impossible for a meteoroid to penetrate deep into the atmosphere, which it
would have to in order to cause a sonic boom that could be heard on the ground.
I've tried to represent this situation with a diagram (sorry for the poor quality - I don't know how to draw straight lines with my software that are
not horizontal/vertical), where "A" (in red) represents a location where the radiant will be well below the horizon for an observer at that location,
and the green arrows represent the direction/trajectory of meteors.
As you can see, at the location in question, a meteoroid would be traveling upwards and out of the atmosphere, although it may have been low enough to
produce sonic booms well before reaching this location, but too far to be heard at location "A".
Earth Grazing Meteors
One of the more fascinating aspects of our gently curved meteor meniscus is the fact that it will permit the viewing of meteors whose radiant is
actually below the horizon of the observer. From Figure 1, it can be seen that a shower radiant which is exactly at the horizon, to either left or
right, will still generate meteors which strike our meniscus horizontally, but "illuminating" only 1/2 of our observable sky. Meteors which are seen
near the horizon will have some small entry angle into the atmosphere, but those meteors which occur nearly overhead will be travelling almost
perfectly horizontal. These grazers can traverse unusually long paths through the atmosphere because they are skimming horizontally through less dense
portions of air , rather than penetrating downward to denser layers. These meteors are quite spectacular to observe and can occasionally cover more
than 100 degrees of arc for an observer below.
As the shower radiant dips below the horizon, it will, for a time, still be able to illuminate some portion of our meteor meniscus -- as long as the
entry angle of the meteors into the atmosphere remains at 0 degrees or higher. This permissible region of sky shrinks as the meteor radiant drops, and
the resulting meteors will occur at greater and greater distances from the observer. Finally, the shower radiant will reach a critical angle below
which it can no further illuminate our observable sky, and the show will be over until the radiant once again begins to rise -- with the first
possible meteors from the shower occurring when this critical angle is again reached.
Source: The American Meteor Society
Of course, this does not rule out meteoroids from other meteor showers (there are a handful of meteor showers active right now), but for the reasons I
pointed out at the top of this post, they are not
a likely source either.
A much more likely source is a small asteroid or asteroid fragment since asteroidal material is generally less fragile than cometary material (which
is the source of most annual meteor showers), and so can penetrate deeply enough into our atmosphere to cause sonic booms that may be heard/felt on
However, there is still no evidence to suggest that the booms in question were caused by an extraterrestrial body entering the atmosphere, although it
remains a distinct possibility as far as I can see.
A satellite/junk reentering the atmosphere may be a possibility, but not a very likely one since there were no reentries forecast for the time period
as far as I'm aware.
I'd like to know how widely spread the sonic-boom reports were - if they were only over a small area, perhaps it was a military aircraft breaking the
sound barrier. If they were spread out over a large area, then that would suggest that an object entering the atmosphere cause the booms.
edit on 20-10-2012 by FireballStorm because: ran out of room