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(meteorobs) 73P/SW3 meteors: 1930 event



The term of a rich meteor display connected with Comet
73P/Schwassmann-Wachmann 3 in 1930 needs caution.

When we look into the original Kyoto Bulletins of 1930,
we find an interesting note in Bulletin 172 about enhanced 
meteor acitivity.  T. Miyasawa observed faint meteors on 
May 21, 1930, from a radiant at alpha=219.75, delta=+29.67.
The estimated orbit seemed close to SW3's.

In Bulletin 173, we find details: Miyasawa observed 
14 meteors/1.13 hours (particular period: 11/0.42 hours),
and his colleague K. Nakamura, 100+/0.42 hours. They
claim it was 'impossible to record all of them'. They
noted 'rapidly declining activity on later days' drawing
the conclusion that the meteors are of 'other origin that 
the above mentioned cometary orbit' (SW3, whose orbit
was passed on June 9). 

The predicted radiant according to Kyoto Bull. 171 is
alpha=234.5 delta=+44 (typo corr. in Kyoto Bull. 173); if
we use their parabolic orbit (Bull. 171) for a modern
radiant prediction by the programme of
  NESLUSAN L., SVOREN J., PORUBCAN V.: 1998, "A COMPUTER PROGRAM
  FOR CALCULATION OF A THEORETICAL METEOR-STREAM RADIANT", ASTRON.
  ASTROPHYS. 331, 411-413.
we get alpha=219, delta=+45. If we use the orbit given 
by Kronk (http://comets.amsmeteors.org/meteors/showers/tau_herculids.html)
we get alpha=220, delta=+44.5, minimum distance between the
orbits of Comet and Earth 0.005 AU. As the peak time was
predicted for about June 9, a report by K. Nakamura emerges:

On 1930 June 9 he reports 59/1.00 hours; on 1930 June 10 he
reports 36/0.50 hours. These rates of 60-70 meteors per hour
are generally cited. However, the observations by K.Nakamura
should be carefully scrutinized. A similar report for the June
Bootids (Pons-Winneckids) in 1921 came from him which turns out
to be most questionable. He always claims all meteors were
very faint. Consider the comments about the SW3-meteors:
'all of those meteors were very faint, and only few of them
were as bright as 4th magnitude'. There was Full Moon on June
9/10. He writes about 'June 9 and June 10 when bright lunar haloes
were high abobve the southern horizon.' Even observers with
very high perception will hardly be able to spot a considerable
number of +5 and +6 meteors under such poor conditions (Moon
and cirrus).

Another item makes me extremely cautios. I checked the original
plots of Nakamura for the June Bootids and found that what he
calls high activity consists of many many meteors which start
WITHIN the radiant and move out of it for about 10 degrees.
Every today's meteor observer knows that this is nonsense. His
companion observer, I. Yamamoto, provides much more consistent
plots, though an activity around 10 at best for the 1921 June 
Bootids.

Apart from the activity enhancement in May 1930, we should
conclude there was NO ACTIVITY from Schwassmann-Wachmann 3 
on June 9/10. This is supported by Yamamoto's comment that
Nakamura 'was practically the sole observer of this rich display.'

Nevertheless, the investigation of Schwassmann-Wachmann 3
activity will be most interesting for the current and forth-
coming years. If we use the current orbit of the Comet
(IAUC http://cfa-www.harvarddot edu/iau/Ephemerides/Comets/0073P.html)
with the above mentioned programme, we obtain raadiants at
alpha = 209  -- 211, delta = +21 -- +29, minimum distance
0.042 AU (ten times larger than in 1930), Vinf = 17 km/s
(which is entry velocity into the atmosphere, whence relevant
to the observer).

Finally, I wish to express my recommendation to be critical
with one's own observations at any time. In charge of collecting
meteor observations from around the world, I occasionally encounter 
similar questionable contributors, unfortunately, from the
very place of the world as in 1921 and 1930. 


Rainer Arlt

-- 
Rainer Arlt  --  Astrophysikalisches Institut Potsdam -- www.aipdot de
Visual Commission - International Meteor Organization -- www.imodot net
rarlt@aipdot de --  phone: +49-331-7499-533  --  fax: +49-331-7499-526
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