Electronic Telegram No. 4293
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
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Prepared using the Tamkin Foundation Computer Network


2016 PERSEID METEORS
     P. Jenniskens, SETI Institute and NASA Ames Research Center, reports that
the 2016 Perseid meteor shower is expected to be more active than in other
years.  Jupiter's gravity will move the core of the Perseids towards the
earth's orbit in 2016, as it did before in 1980, 1992, and 2004.  Rates in
2004 increased to a zenith hourly rate (ZHR) of 110 Perseids/hour, instead of
the normal ZHR = 80-90 meteors/hr (cf. information at the following website
URL:  http://www.imo.net/news/perseids2004-4).  The broad annual shower
maximum is centered on Aug. 12 at 12h-18h UTC (solar longitude 140.00-140.19
degrees, equinox J2000.0).  Even before midnight, the moon will not disturb,
because it will be low in the sky for northern-hemisphere observers.
     More significantly, encounters are possible with the one-, four- and
seven-revolution-old dust trails of comet 109P/Swift-Tuttle and with the
accumulated Perseid Filament of older dust in mean-motion resonance.  In
calculations by J. Vaubaillon (Institut de Mecanique Celeste et de Calcul des
Ephemerides, Paris Observatory), the one-revolution dust trail is encountered
on Aug. 11 at 22h36m UTC, but the dust density is expected to be low.
High-ejection speeds would be required to delay the dust this far behind the
comet position after only one orbit.  Instead, Vaubaillon predicts a small,
0.00023-AU miss distance and significant activity from crossing the older
seven-revolution (1079) trail on Aug. 12 at 4h43m UTC, or solar longitude
139.683 deg (c.f., Jenniskens 2006, *Meteor Showers and their Parent Comets*,
Cambridge Univ. Press, p. 657).
     Calculations by M. Maslov (Novosibirsk State Technical University)
confirm that the earth will pass the one-revolution (1862) ejecta at only
0.00134 AU distance on Aug. 11 at 22h34m UTC, but expects a measurable
increase in rates.  In addition, lower ejection speeds are sufficient to
bring dust from the four-revolution (1479) trail into the earth's path, on
Aug. 11 at 23h23m UTC.  Both profiles may be merged into one outburst
component with peak ZHR of about 40 Perseids/hr over normal activity. For
additional information, see the following website URL:
http://feraj.narod.ru/Radiants/Predictions/Perseids2016eng.html.
     Higher rates are predicted in calculations by D. Moser and B. Cooke
(Marshall Space Flight Center, NASA).  They estimate a peak ZHR of 135
Perseids/hr, centered on Aug. 12 at 0h UTC for the main outburst, supporting
the hypothesis that the event is caused by meteoroids of the one- and
four-revolution-old trails.  The seven-revolution trail would peak at about
4h UTC, when rates could increase briefly to ZHR = 40 Perseids/hr over normal
annual activity.  More info can be found at the following website URL:
http://www.asu.cas.cz/~borovic/Meteoroids2016/Invited/02_INVITED_Cooke.pdf
     According to Jenniskens, the time of passing the Perseid Filament
remains uncertain.  Based on a 3-hr-wide peak seen in 2004 at solar longitude
139.64 deg, the Filament may return with a ZHR of about 30 Perseids/hr on
Aug. 12 at 4h-5h UTC.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2016 CBAT
2016 August 9                    (CBET 4293)              Daniel W. E. Green