[Prev][Next][Index][Thread]

Re: (meteorobs) Re: Request for comments: "Hot Falling Stars of Summer"

Norman wrote:
> I really hesitate to accept it at face value with the less-than-thrilling
> rates that I usually see in excellent skies.  The Perseids are a reasonably
> good shower with occasional better displays.  Definitely not a  "reliable"
> shower, in the sense of  "best of the year",  which I so often read about in
> popular literature.

Reliable in my dictionary means trusty, dependable.  It was the shower
that beginners or casual observers would select (not least because of
holidays and warmer nights).  You knew that you'd always see a good
display and occasionally a stunning one.  50 m/h including sporadics
and minor showers is a good display compared with a typical night.
Given dark skies at Perseid maximum, I can't recall a mediocre
display.  This was before 1989 and the second peak observing from
latitude 51.5 to 52.5N under +6.5-7.0 skies.  The 1972 maximum was
memorable with over 600 meteors in about 5.5 hours.  In some ways
the second peak made the Perseids unreliable in the sense we didn't know
what to expect in the way of a peak ZHR.  If you want to extend the
definition of "reliable" I'd prefer "consistent" rather than "best".

Norman how does your perception coefficient change with shower speed?
Are you relatively poorer at seeing fast-moving meteors compared with
the average?

> I would have seen about 86% of those meteors in sky LM6.5, borrowing my own
> correction factor determined from observed sporadic meteors empirically,

Does this allow for the brighter/smaller mean magnitudes/population indices
of the Perseids compared with sporadics?

> My long-term baseline for an average Perseid shower,  back to 1964,  is
> 40/hr observed at the max.  The popular quoted peak rate before 1977 was
> usually 50.   The years 1969, 1977,1978, 1981, 1989,and 1997 were the good

Unfortunately, most of my meteor papers are in storage.  The following
is from memory.  Ignoring books which merely copied earlier books
without checking modern results, the ZHRs quoted during the early
1970's were between 60-70.  This is in line with the 40/h observed.
There appeared to be a trend of improving Perseid ZHRs of about 80 in
the late '70s and early '80s, and then a fall back, until the second
peak came along.

In the early 1970s, the nominal Geminid ZHR was around 55.  That's
changed, which is part of the fun of observing.  The skies are never
the same. I wouldn't disagree that the Geminids are currently the best
year in year out, and that many books still use long out-of-date
hourly rates.

Paul Roggemans was doing an analysis of pre-IMO data using current
standard reductions to investigate the longer-term activity variations
in the Perseids.  (Has anyone taken this over since Paul's
retirement?)  It'll be interesting to get the global picture over a
longer timescale.  You can't draw many conclusions about peak rates
from one or two observers at one location.

> years.  The 1990's have all been below my average until 1997.  None of the
> recent outbursts have occurred when I was watching.

Must be a conspiracy. (-:

Malcolm
References: