Fw: [meteorite-list] meteor velocity
From: GeoZay_at_aol.com <GeoZay_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:44 2004 Message-ID: <b0.409aef7a.2cd9a682_at_aol.com> -------------------------------1067994242 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Hello Jose, I=E2=80=99m not sure of the source...perhaps from IMO=E2=80=99s Meteor Obser= ving Guidebook?=20 I don=E2=80=99t have a copy handy anymore, So I=E2=80=99m gonna try to wing=20= it with the=20 interpretation that I got from it all.=20 Basically, meteoroids coming from parent objects in the asteroid belt, have=20= a=20 relatively slow orbital speed when compared to particles that come from=20 in-coming comets that are in long range orbits around the sun. I believe thi= s is=20 shown in one of Keplers Laws? Most of the asteroids in the asteroid belt and= =20 near earth, orbit the sun in the same direction as the planets. For any of t= hese=20 asteroidal objects to enter the earth=E2=80=99s orbit, they would have to pl= ay =E2=80=9CCatch=20 up=E2=80=9D with the earth. Thus they would tend to enter the earths atmosph= ere=20 during a period from afternoon to before midnight. Subtracting their orbita= l=20 speed, which is in the vicinity of earths orbital speed, would mean they wou= ld be=20 entering at velocities that would appear very slow. If they are entering=20 directly behind the earth, then the speed would be no faster than about 11 k= m/s. The=20 exact velocities can vary a little since the exact entry angle from behind=20 could be a little off. For the most part, for an asteroidal meteoroid to=20 survive the rigors of passing thru our atmosphere, they should have velociti= es less=20 than 29 km/s. Any faster they would have the tendency to burn up or explode.= A=20 meteoroid entering the earths atmosphere at velocities near 11 km/s would=20 appear to move quite slowly to the eye. Those that have entry velocities of=20 around 29 km/s would appear to be moving at best from medium slow to medium.= That=E2=80=99 s what you can expect from an asteroid that produces meteorites. To the best= =20 of my knowledge, these are the only kind of meteorites, with a few exception= s=20 such as those from the moon and mars. As for the meteors that come from=20 comets. The parent comets and their particles that are in the similar highly= =20 elliptical orbits come from way out...most beyond Neptune with a few excepti= ons. By=20 the time comets and their particles get in the vicinity of the earth, they h= ave=20 a much higher velocity than an object with asteroidal origins. Again one of=20 the Kepler laws. Comet particles tend to meet up with the earth coming from= =20 all directions....behind, straight on and obliquely. These different directi= ons=20 basically dictate the entry velocites in the long run. They can enter from=20 behind and have the same velocity as an asteroidal object. They can enter fr= om=20 the front with a velocity up to 72 km/s....way faster than what an asteroida= l=20 object can. In order for an asteroidal object to have this kind of velocity=20= from=20 behind, it would mean it is no longer in orbit around our sun. It=E2=80=99s=20= basic=20 orbital velocity in the vicinity of earth and the asteroid belt is locked in= at a=20 slower velocity than something coming in from beyond Neptunes orbit. Now=20 with this all said, If Mike said he saw a meteor appear to be traveling Very= =20 Fast....then its not likely to be of asteroidal origin, nor drop any meteori= tes.=20 Most likely of cometary origin. It is possible to have a cometary particle=20 entering the earth with Slow to Very Fast Velocities, but highly unlikely fo= r an=20 asteroidal particle to have anything other than Slow to maybe Slow to Medium= =20 velocities. I don=E2=80=99t know how fast Mike=E2=80=99s fireball was travel= ing, but do know if=20 one has seen a few meteor showers, you can quickly gain a =E2=80=9Csense=E2= =80=9D of whether=20 it=E2=80=99s traveling Very Slow(typical meteorite dropping velocity) to one= that is=20 Very Fast(cometary velocity with no meteorite survival expected). I hope my=20 wording makes some sense?I don't have the math expertise, but I believe I=20 understand the concepts quite well? :o) George Zay -------------------------------1067994242 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en <HTML><HEAD> <META charset=3DUTF-8 http-equiv=3DContent-Type content=3D"text/html; charse= t=3Dutf-8"> <META content=3D"MSHTML 6.00.2800.1106" name=3DGENERATOR></HEAD> <BODY style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial; BACKGROUND-COLOR: #fffff= f"> <DIV> </DIV> <DIV> </DIV> <DIV>Hello Jose,<BR>I=E2=80=99m not sure of the source...perhaps from IMO= =E2=80=99s Meteor Observing Guidebook? I don=E2=80=99t have a copy handy any= more, So I=E2=80=99m gonna try to wing it with the interpretation that I got= from it all. <BR>Basically, meteoroids coming from parent objects in the as= teroid belt, have a relatively slow orbital speed when compared to particles= that come from in-coming comets that are in long range orbits around the su= n. I believe this is shown in one of Keplers Laws? Most of the asteroids in=20= the asteroid belt and near earth, orbit the sun in the same direction as the= planets. For any of these asteroidal objects to enter the earth=E2=80=99s o= rbit, they would have to play =E2=80=9CCatch up=E2=80=9D with the earth. Thu= s they would tend to enter the earths atmosphere during a period from aftern= oon to before midnight. Subtracting their orbital speed, which is in t= he vicinity of earths orbital speed, would mean they would be entering at ve= locities that would appear very slow. If they are entering directly behind t= he earth, then the speed would be no faster than about 11 km/s. The exact ve= locities can vary a little since the exact entry angle from behind could be=20= a little off. For the most part, for an asteroidal meteoroid to surviv= e the rigors of passing thru our atmosphere, they should have velocities les= s than 29 km/s. Any faster they would have the tendency to burn up or explod= e. A meteoroid entering the earths atmosphere at velocities near 11 km/s wou= ld appear to move quite slowly to the eye. Those that have entry velocities=20= of around 29 km/s would appear to be moving at best from medium slow to medi= um. That=E2=80=99s what you can expect from an asteroid that produces=20= meteorites. To the best of my knowledge, these are the only kind of meteorit= es, with a few exceptions such as those from the moon and mars. As for= the meteors that come from comets. The parent comets and their particles th= at are in the similar highly elliptical orbits come from way out...most beyo= nd Neptune with a few exceptions. By the time comets and their particles get= in the vicinity of the earth, they have a much higher velocity than an obje= ct with asteroidal origins. Again one of the Kepler laws. Comet partic= les tend to meet up with the earth coming from all directions....behind, str= aight on and obliquely. These different directions basically dictate the ent= ry velocites in the long run. They can enter from behind and have the same v= elocity as an asteroidal object. They can enter from the front with a veloci= ty up to 72 km/s....way faster than what an asteroidal object can. In order=20= for an asteroidal object to have this kind of velocity from behind, it would= mean it is no longer in orbit around our sun. It=E2=80=99s basic orbital ve= locity in the vicinity of earth and the asteroid belt is locked in at a slow= er velocity than something coming in from beyond Neptunes orbit. Now w= ith this all said, If Mike said he saw a meteor appear to be traveling Very=20= Fast....then its not likely to be of asteroidal origin, nor drop any meteori= tes. Most likely of cometary origin. It is possible to have a cometary parti= cle entering the earth with Slow to Very Fast Velocities, but highly unlikel= y for an asteroidal particle to have anything other than Slow to maybe Slow=20= to Medium velocities. I don=E2=80=99t know how fast Mike=E2=80=99s fireball=20= was traveling, but do know if one has seen a few meteor showers, you can qui= ckly gain a =E2=80=9Csense=E2=80=9D of whether it=E2=80=99s traveling Very S= low(typical meteorite dropping velocity) to one that is Very Fast(cometary v= elocity with no meteorite survival expected). I hope my wording makes some s= ense?I don't have the math expertise, but I believe I understand the concept= s quite well? :o)</DIV> <DIV>George Zay<BR></DIV></BODY></HTML> -------------------------------1067994242-- Received on Tue 04 Nov 2003 08:04:02 PM PST |
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