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Re: (meteorobs) Re: What? A Leonid storm in *1886*?!?


Letter to Meteorobs:

        Concerning the possibility that the display observed in 1886
were the Leonids, I would like to suggest that the Leonids are
ruled out on three grounds:

1)  Solar radiation pressure segregates the particles according to
their radius, r.  Smaller particles move faster, larger particles move
slower.  The reason is that force is proportional to surface area,
which depends on r**2, while mass depends on volume, or r**3.
Now, acceleration is a powerfull effect because the distance covered
is proportional to time squared.  The 1886 shower took place 20 years
after the comet was at perihelion.  You can imagine the velocity and
displacement distance, after 20 years of acceleration!
Thus the scatter must have been greatest near 1886.  We would then
expect a minor shower, not the storm observed that year.

2) Independent of the above effect, segregation of
particles is an intrinsic phenomena of the comet.  Particles are
propelled by gas, and thus once again smaller particles move faster than
larger particles.   This effect adds to the above one, and makes
the identification with the Leonids even more improbable.

3) In my A&A paper (Vol. 348, p. 295, 1999) Figure 1 shows the particle
distribution around the comet.  It is entirely possible to find were
the 1886 shower would be located on this plot.  If the plot were 10cmx10cm
the 1886 point would be 29 cms above the x-axis, and 4 cms to the right
of the y-axis.  That is entirely off the plot.  Moreover it is so far
from the "ridge" or region of maximum
concentration of particles [identified with the "dust trails" studied
by Sykes et al.(1990) and Sykes and Walker(1992)], that the identification
with the Leonids is ruled out as entirely improbable.

        At this moment the most probable explanation is that these were
the Andromedids\Bielids, misplaced in time as suggested by Rao and Kronk.  
This seems to me the leading hypothesis at present.

        This identification is strengthened by a comment from Majden, who
quoted a book saying that strong Andromedids\Bielids were seen in 1872,
1885 and 1892.  Since the period of Comet Biela was around 6 years,
1872-6=~1886 in agreement with what was observed.

        Question: At what altitude was the radiant of the Bielids at
3 am on that date and location?  Is this altitute in agreement with
the report?

        I would like to add that it was a pity that Mr. Kingsmill
did not know the sky better, because he mentions the radiant but 
not were it was located.  It could have saved us some trouble !

Ignacio


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Ignacio Ferrin,                        + ferrin@ciens.ula.ve
Center for Theoretical Astrophysics,   + FAX: 58 - 74 - 401286
Faculty of Sciences,                   + Phone: 58 - 74 - 401331
University of the Andes,               + Mailing address: Apartado 700
Merida, VENEZUELA.                     +                  Merida 5101-A
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Quote of the Day: "Those who do not like science fiction, have trouble
                   understanding the future".
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++




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