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Re: (meteorobs) Sporadic V Leonids.
"A&K Wall" <astroman@chariotdot net.au> asked:
>how can you tell that the meteor observed was actually a
>Leonid meteor?
From the NAMN Guide at http://www.namnmeteors.org
<---Begin--->
2) OBSERVED SHOWERS - During your planned observing session, one or more
meteor showers may be active. If you plan on trying to keep track of
multiple showers, attention must be paid to the proper assigning of each
meteor you see. For those just starting out, it is usually easier to
watch for one shower only, recording all other meteors as sporadics.
Somewhat difficult at first, classification of a meteor becomes easier
with practice. When a meteor shower occurs, all shower members radiate
from a central location known as the radiant. By knowing where a
shower's radiant lies, a meteor can be projected backward along the path
it traveled to see if it crosses the radiant. Radiant diameters vary
depending on the shower. Most are in the neighborhood of 5 degrees in
size, although some are as large as 15x10 degrees. If a suspected meteor
is traced back toward this radiant, count it as a shower member.
Otherwise it should be considered a sporadic meteor. Care should be
taken on nights when more than one meteor shower is active. On these
nights, all radiants in the area of sky that is being covered should be
accurately identified prior to the watch.
There are three criteria used in determining if a sighted meteor belongs
to a particular meteor shower or not. The three things to consider are:
a) RADIANT - First of all, the meteor must line up with a radiant. As
mentioned previously, most meteor shower radiants are about 5 degrees in
diameter. As a guide, keep in mind that 10 degrees is approximately that
of a fist held out at arms length.
b) VELOCITY - Each meteor shower produces meteors that are all close to
the same velocity. The velocity of a meteor is dependent not only on its
own velocity, but also that of our planet as it moves through space. You
can use a scale of 1 - 5 to assign velocity to a meteor. Very slow
(visible for several seconds) would be assigned a 1, slow a 2, 3 for
medium velocity meteors, 4 for a rather fast one with a meteor head
visible and 5 for those moving very fast, just leaving streaks with no
visible head.
c) METEOR LENGTH TO RADIANT RELATIONSHIP - The closer a meteor emerges
from its radiant, the shorter in length the meteor will appear. If it
appears right in the radiant, it will appear as a star suddenly
brightening and then disappearing (known as point meteors). The further
a meteor appears from the radiant the longer the path of the meteor
normally appears. Associating meteors with a shower using meteor length
is difficult at first, but with practice becomes second-nature. A useful
rule to remember is one developed by the International Meteor
Organization which states:
"For radiant elevations higher than 30° the apparent path length l of a
shower meteor amounts at most to half the distance from the radiant to
the start point. Consequently, the distance between radiant and start
point of a plotted meteor on the chart has to be at least twice as long
as the meteor path itself if the meteor is a suspected shower member."
<---End--->
Hope this helps!
Mark Davis
sc.meteors@home.com
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