(meteorobs) Interesting facts about meteor shower

[LarryFarma at aol.com]

In a message dated 9/1/04 6:45:32 PM Pacific Daylight Time,
     pbias at flsouthern.edu writes:

> Hi Larry,
>  We really don't need another explanation since we already have the correct 
> one.  
>   
>  You are right that meteors will appear all over the sky--they do during 
> meteor showers.  BUT they appear to be coming from the direction of the 
> radiant, not directly starting out of the radiant itself.    That is, only 
if 
> you trace the meteor trails back will you find that they more or less 
> intersect in a small section of the sky, the radiant.

Pete,

             Thanks for the explanation.     I think that many 
references about meteor showers do not point out that the 
meteors start all over the sky,   and I think that many people 
who have not viewed a meteor shower have the false impression 
that the meteors start in or near the constellation that the
shower is named for.                  
            I presume that meteor showers were discovered by 
visual observation and not by photography,   where the great 
frequency of meteors becomes obvious and the meteor directions 
are recorded.     I wonder how the showers were discovered and 
named in the first place.     Well,   maybe some 
astronomers and/or hobbyists  counted meteors in the 
wee hours of every night  to see if some nights of the year 
had a greater frequency of meteors than others.        
   
   
>  You are also right that the earth will pull the meteoroids toward its 
center 
> as they approach, BUT that won't be very obvious to a single observer that 
is 
> able to see only a very small section of the earth's atmosphere.  All the 
> meteors visible from a particular location will be pulled about the same 
> amount and thus still remain parallel to one another in space.  If you 
could 
> view the meteors from all sides of earth at once you probably would be able 
> to see differences in how they approach.  We simply don't have this 
> opportunity.

             Maybe there is such an opportunity --- any change 
in direction of the meteoroids at a given place and time 
could be determined by a shift in the point of the sky that they 
appear to diverge from.     Such determination would probably 
require photography,   which provides a precise record of the 
meteors' directions.      The directions of the trails at different 
times of night could be compared to see if there is a 
direction change resulting from a shift of the observation point relative 
to the meteoroid stream.      Such shifts of direction might provide 
a means of estimating the meteoroids' speed relative to the earth 
prior to the influence of gravity.     For example,   if this speed 
were very high,   the influence of gravity on the meteoroids' 
directions would be small    Also,  the duration of a meteor could 
be used to estimate the speed of the meteoroid when   
under the influence of gravity and aerodynamic resistance.      For 
example,   if a meteor lasts one second and is estimated to have a path 
length of about 7 miles,   then the average speed of the meteor 
would be of course be 7 miles/sec.,  about the same as the 
minimum speed required for escape from the earth's gravitational 
field.   

            On an unrelated topic,   I am trying to figure out how 
astronomical 
measurements could be made with sufficient accuracy to predict 
the transits of Venus across the sun,   particularly using the 
technology of the 1600's and 1700's,   when these transits were 
first predicted ( they occur at alternating intervals of about 
122 years and 6 years ).     The world is a weird place and 
keeps getting weirder.     

              Thanks.

Larry Fafarman

>   
>  Pretty sure we've at least figured this part out about meteors.
>   
>      Pete Bias
>      Lakeland, FL