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(meteorobs) Re: 2003 Perseids not much in [Insert your home town here]

Norman wrote:

> Prior full-moon Perseid maxes (moon phases and dates repeat in a 19-year
> cycle) : 1984 peak Perseid rate 9/hr for 3 hours ; 1965 - came home to
Miami
> in the evening after summer school but did not observe; 1946 - only 2
months
> after I burst upon the world scene (June 3 birth).  Had not realized the
> latter until yesterday.  The nearly full moon 2 months later dulled the
1946
> Draconid storm as well.  Go back 2 more cycles to 1908, and my father had
> just been born before the washed-out 1908 Perseids.  Three years later, in
> 1911 with a waning gibbous moon, Denning in England complained that the
> Perseids had disappeared; all references to that year that I have seen
> neglect to mention the moon so readers will think something drastic had
> happened to the Perseids.

    Thanks, Norman, interesting stories. I know Moon phases very well, my
favourite hobby is detecting orbital patterns. In the case of the Moon most
of you will recognize that 19 years is the Metonic cycle, which is reflected
in a number of lunar calendars in various parts of the world. Those
calendars follow a cycle not unlike a "tala" (a sub-divided rhythm in Indian
classical music), inserting leap months at intervals of 3, 3, 2, 3, 3, 3, 2
years. The Moon itself does more or less the same thing, approximately,
something quite significant to meteor observers who really tend to be
watchers of the solar calendar. A quick Google search brought the following
headline from 2000: "The Perseids Contend With A Bright Moon This Weekend."
The periods of 8 and 11 years are particularly close, with phases within a
day or two.

    The other cycle which can be superposed on this is the (local) time of
the maximum, which advances at 6h per year, resulting in a repetition every
four years, in step with the leap year.After this year's peak at 5h UT, I
know next year's peak will be around 5:00 Mountain Daylight Time,
traditionally closing time for us with the radiant nearing the zenith but
the daylight coming up behind it. This would last have happened in 2000 when
the Moon was bright, but next year the Moon should be just a late-rising
crescent. Because the Moon's tala is out of phase with the leap year's
steady 4/4 backbeat, one's local experience of observing during the peak
hours will eventually take the floor with the entire ensemble of lunar
phases.  But it should be noted that the interval of eight years will give
reasonably similar conditions for moon phase and peak time.

    Presumably the experts -- of which I am not one -- discount the annual
difference of 5h49m, with any residual difference representing actual
evolution of the meteoroid stream.  Come to think of it, this should show up
directly in the radiant's ecliptic coordinates.

    Back to the 19-year cycle for a moment, this approximates the 18.6-year
lunar cycle known as the regression of the nodes, during which period the
Moon fluctutaes +/- 5° of the ecliptic in a given spot. Thus the Full Moon
of the 1984 Perseids and of the 2022 Perseids should be the same *altitude*
as tonight, rise at the same local time, etc.

    The last cycle which I daresay everybody has noticed is the
nine-lunation cycle: shouldest it be fated that the Leonids are wash-ed out
by Full Moon, then be it in like wise that the Perseids shall so be
afflicted.

    More on my own wash-ed out observations tomorrow, once I transcribe my
notes. (Obviously, it's getting late!) Suffice to say for now, not a good
showing.

    regards, Bruce


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