[meteorite-list] Meteor showers and meteorite falls

[Rob McCafferty]

The range of speeds for incoming meteoroids is
12-72km/s. 12 being the escape velocity at the earth.
Any object moving with the earths speed and in the
same direction, if it were to collide with the earth
would fall at this speed. Any object travelling slower
than the earth will only hit the leading side at
12km/s plus the difference in orbital speed.
Particles travelling faster than the earth can hit
either side with 12+earths orbital speed + initial
orbital velocity. This initial orbital velocity can be
anything up to the escape velocity fr the suns
gravity.
I forget the earths orbital speed but the max speed
available is 72km/s and I undertand the leonids have
about this.
This is consistent with a high velocity trail coming
at us head on which explains the sharp peak on the
leading side of the earth.
The upshot of all this is that (like the car window
collecting randomly moving bugs), the earth collects
more detritus on it's leading side, so any random 
meteor is more likely to be seen after Midnight local
time and I suppose, you ought to see big fireballs
more frequently in the early morning too (by which I
mean daylight)
Whether this leads to more recovered falls I couldn't
guess at. The requirements for recovery being quite a
narrow window of parameters, the high speed of those
hitting head on is likely to render them vapour well
before they become -ites. But I cannot be definitive
on this.

It is worth pointing out that while planets and
(generally) asteroids, all follow the same orbital
direction around the sun, comets can perform their
orbits from any direction. High above or below the
ecliptic and with or against the normal planetary
direction. This is why it is possible to have such a
large range of incoming speeds but it'll be comet
fragments which occupy the higher ranges only.

Rob McC

--- MexicoDoug <MexicoDoug at aim.com> wrote:

> Doctor Death wrote:
> 
> "Somewhere I recall that the best time to watch
> meteors is around 4:00 am 
> where the Earth is facing foward in orbit."
> 
> "And the most likely time for a  retrivable fall is
> 4:00 pm when a meteorite 
> is approaching earth is catching up to it in orbit. 
> Kind of like retriving 
> bugs off the front and  back windshields. Anybody
> care to back me up on 
> this?"
> 
> Statistically I'm sure you're right, so I'll back
> you up.  If you run into a 
> uniform wind in your face when it is raining you get
> wetter and pelted 
> harder than if you run away...
> 
> If we say everything solar is traveling around with
> similar orders of 
> velocity as earth in its orbit (66,000 miles per
> hour - over 100,000 
> km/hour) this is true.  Of course if Earth's
> velocity were negligable it 
> wouldn't matter.  That's the difference with bugs
> which can't catch up to me 
> and still have enough flight enery to squash
> themselves on my rear 
> windshield when I drive , but meteoroids do catch up
> to the earth with 
> probability of some trigonometric function,
> calculated with relative speeds 
> and radiants...depending on the time of day.  I have
> consistently whipped 
> meteoroids and they are too afraid to respond to my
> dares, as well as bugs, 
> catching up, driving during the day - but it remains
> to be seen if 
> meteoroids can catch up.  Maybe I'll give them a
> handicap, drive east at 
> about 10PM at low latitude, and then check my
> radiator grill for chondrules 
> and inclusions...
> 
> Which brings up the other factor when observing
> meteors and which also comes 
> into play for bolide production and meteorites.  At
> the Vernal Equinox (the 
> first day of Spring), an observer north of the
> tropics see the least because 
> the "windshield" tilt adds to the angle, but on the
> first day of Autumn 
> (Autumnal Equinox) in the north, (s)he see the most
> meteors because the 
> "windshield"is tilted the least as we plow through
> our orbit.  A true, 
> efficient meteor hunter could always get a front
> seat if needed.  This 
> happens because earth is tilted.  So if you want to
> increase odds, consider 
> the benefits and drawbacks to work around Sept. 22,
> after midnight:-)
> 
> Actually the windshield of our great blue spaceship
> is the atmosphere, and 
> the the interstate highway out here follows a feeder
> ring outside of 
> downtown business end of the Solar System where
> people would be fried to a 
> crisp.  The route the spaceship follows could be
> called "Apex route" since 
> it follows the apex vector - the point connecting
> the center of the Earth 
> with the most forward point in the orbit which
> changes every instant during 
> rotation and revolution!
> 
> Best wishes, Doug
> (hope I got this straight, and of course the
> non-random amount of meteoroid 
> seasonal congestion in earth's annual orbit will
> also have effect on rates)
> 
> 
> ----- Original Message ----- 
> From: "doctor death" <neocondeatheaters at hotmail.com>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Friday, November 17, 2006 2:22 PM
> Subject: [meteorite-list] Meteor showers and
> meteorite falls
> 
> 
> > Meteorite showers from Comet trails might be CM2 
> or CI1 types if this
> > happens. Not big rocky ones like observed bolides.
> Perhaps more dust in 
> > the
> > raingutters. Somewhere I recall that the best time
> to watch meteors is
> > around 4:00 am where the Earth is facing foward in
> orbit. And the most
> > likely time for a  retrivable fall is 4:00 pm when
> a meteorite is
> > approaching earth is catching up to it in orbit. 
> Kind of like retriving
> > bugs off the front and  back windshields. Anybody
> care to back me up on
> > this?
> >
> >
>
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