(meteorobs) Meteor report from near Nanton, Alberta, 2008-08-11/12

[pmartsching at mchsi.com]

    Heavy clouds in north-central Alberta this week forced those of us keen
to observe the putative Perseids peak on the night of August 11/12 into
travel mode. Fortunately there was a critical mass of three observers --
Alister Ling, Ross Sinclair, and myself -- who just nicely fit into
Alister's Subaru with room for our equipment. (Sometimes it's nice to not
require a telescope!) We left just after supper on Monday evening for a
five-hour drive, a five-hour observing session, and a five-hour return trip.

    The ever-prepared Alister had overlaid satellite imagery with a road map
and a light pollution map to pick out an excellent spot about 15 km  WSW of
Nanton, Alberta, where clear skies did indeed prevail. The area is in the
foothills of the Rocky Mountains, where the altitude is about double the
~700 metres it is locally. The fact that we were over 3° south of our normal
sites meant we had to wait a little longer for the Moon to set, but once it
did we got a solid three hours of magnitude 6.7 skies before the start of
morning twilight. It was quite marvellous.

    Alister and Ross set up their cameras for a little meteor photography
while I settled in immediately to begin the count. Over the next 4.5 hours I
observed 256 meteors including 229 Perseids; not quite the spike of activity
that was reported from Europe the following morning, but an impressive show
nonetheless (over the past two decades of observing on peak night, only
those of 1994 and 2004 yielded higher personal gross counts). My initial
impression was that it was a bright show, but due to significant numbers of
faint meteors (I even saw a handful that I adjudged at mag +6), the average
Perseid was a surprisingly pedestrian magnitude +2.3.

   Averages notwithstanding, there were plenty of bright ones in the mix,
including 20 of negative magnitude and another 20 of magnitude 0. The best
was a gorgeous emerald green fireball of mag -6 with a persistent train that
lasted some 25 seconds to the naked eye. Fortunately this occurred within
the field of view of all three of us (in Andromeda) so we all saw it in
direct vision. Alister may also have captured an image of this beauty. While
the train was dissipating another -1 Perseid with a 1.5 second train blazed
a short distance away.

    I and at least one other observer witnessed three more fireball-class
Perseids; one white -5 with a 15-second train, an orange -5 with a 6-second
train, and a coppery -4 with a briefer 2-second train. In all I noted
persistent trains on over one-quarter (~60) of observed Perseids.

    I'm sure this percentage is on the low end, as there were times that my
taped notes were insufficiently descriptive due to clumping of meteors; at
one point in my tape I was trying to record details of five different
meteors that I had seen within 6 or 8 seconds, and there were several other
bursts of 3 or 4 in a similarly short interval. My observing partners also
experienced such clumps, and there were at least two occasions when Ross or
Alister saw 4 or 5 in succession where I saw just one or none. The best
burst came around 10:00 UT when we probably saw 10 different meteors among
the three of us in no more than 10 or 12 seconds. They were going off all
over the place, and so were we.

    Summarizing the Perseids by 15-minute bins:

Interval                PER       Mean        Comments
---------------------------------------------------
0630-0645              8        +2.50
0646-0700              3        +3..33
0701-0715              9        +1.89
0716-0730            17        +2.24
0731-0750*          20        +3.05        * inc. 5-minute break
0751-0805              8        +1.62        -6 fireball
0806-0820            11        +2.45
0821-0835            19        +2.05        -5 fireball
0836-0850            16        +3.06
0851-0905            16        +2.69
0906-0920            23        +2.52
0921-0935            11        +2.09
0936-0950            15        +2.40
0951-1005            20        +1.40        -4 fireball
1006-1020            10        +2.10        -5 fireball
1021-1035            10        +2.50
1036-1050              7        +1.43
1051-1105              6        +1.33
-------------------------------------------------

    Re-sorting the numbers into half-hour bins removes much of the "jitter"
in the data and yields surprisingly smooth and consistent results of ~one 
meteor
per minute as the radiant rose during the dark hours:

30-minute bin    PER    LM    Comments
-----------------------------------------------
0630-0700        11      6.0
0701-0730        26      6.3   Moonset during interval
0731-0805*      28      6.6
0806-0835        30      6.6
0836-0905        32      6.7
0906-0935        34      6.7
0936-1005        35      6.7
1006-1020        20      6.4    LM reducing in twilight
1021-1035        13      5.4    "        "         "       "
---------------------------------------------------

    As the morning light came up Alister spotted a layer of volcanic dust
that was the product of a recent eruption in the Aleutians. Soon thereafter
three tired but content astronomers packed up, and safely split the driving
chores during the long ride home.

    Bruce
    *****

Observer: Bruce McCurdy, MCCBR
Dates: 2008 August 12, 06:30 - 11:05 UT; Teff = 4.5 hours
Location: SW of Nanton, Alberta, Canada, IMO Location Code 53005
   113°57'56" W, 50°16'51" N, Elevation 1349 metres
Limiting magnitude: = ~6.7 SQM = 21.6
Conditions: Clear and v. dark, some moonlight early, twilight late
Method: Visual; microcassette recorder and talking watch