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RE: (meteorobs) query on sporadic meteors



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From: 	Michael Mattiazzo[SMTP:mmatti@yp-connectdot net]
Sent: 	Friday, May 14, 1999 11:07 AM
To: 	meteorobs@jovian.com
Subject: 	(meteorobs) query on sporadic meteors

Hello all,

This is my first query post.

What is the definition of a sporadic meteor?

Does it mean that the meteor observer cannot associate it with any known
meteor streams?

Technically, any known or detectable meteor stream

But aren't all sporadic meteors associated with meteor streams (whether
known or unknown to the observer)?

Hmmm, well yes and no. Is one meteor in an orbit that no other particles 
share a meteor stream? That seems like a clear no. Are 10? Well 
maybe...what if the 10 are spaced in a 200 year orbit so one meteor 
approaches the earth on average every 20 years? What if they are packed 
together and all 20 occur in one night..but are observed at 20 different 
locations?

Meteor Stream> "A stream of solid particles released froma parent body. 
Various ejection directions and velocities cause the width of the stream 
and (along with other factors) the gradual distribution of meteors over the 
entire avaerage orbit"



If I observe 2 sporadics radiating from the same point in the sky during a 
1
hour interval, can I assume that they are related to an as yet unrecognised
stream?

That would not be a good assumption. If however, you observe 2 and 20 other 
people on earth also observe 2 the same night, AND THEY ALL HAVE THE SAME 
VELOCITY, then yes they may well be a shower or outburst. That is exactly 
why we plot meteors, so that worldwide observations can be combined to see 
if any particular activity rises above the background of pseudorandom 
"sporadic" meteors.

If I observe 6 sporadics in an hour, is this count too high?

Not at all...in Autumn, hourly sporadic rates can be much higher than that.

The key really is detectability. A shower with a rate much below 1 an hour 
is undetectable by most means. The rate is so low, photographic records are 
unlikely, and other methods lack sufficient accuracy at such a low rate. So 
they become the sporadics. And there are many particles in their own orbit. 
When streams spread out so much they can't be detected, they become part of 
the soup. When streams get too close to a planet they can be disrupted with 
the particles scatted across the solar system.

A related point, sporadic meteors are not truly random. A large percentage 
fall on or near the ecliptic, since that's where most of the "stuff" of the 
solar system is. And they tend to approach the earth on orbits that cause 
concentrations to appear. In addition, particles that are inserted into 
orbits well out of the plane of the solar system tend to remain in stable 
orbits (since they don't interact with the planets as often), hence there 
is a concentration of particles in what are called "toroidal" orbits.

Not a very organized or satisfying reply, but I'll bet it gives you more to 
think about (and probably will spark a few more question!!)

Cheers and clear skies with plenty of meteors,

I'll take that! Same to you.

Michael Mattiazzo,
Wallaroo, South Australia
mmatti@yp-connectdot net


Wayne T Hally
High Bridge NJ USA
meteors@eclipsedot net


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