(meteorobs) NAMN Notes: August 2004

[Mark Davis]

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NAMN Notes:  August 2004
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Introduction:
NAMN Notes is a monthly newsletter produced by the North American Meteor
Network, and is available both via email, and on the NAMN website at:
http://www.namnmeteors.org


Contents:

1.  Perseids - A Year for Surprises?...
2.  Aquarids and More Aquarids Again...
3.  Other August Meteor Activity...
4.  Upcoming Meetings...
5.  For more info...


1.  Perseids - A Year for Surprises?...

Perseids... the mention of this shower conjures up great memories, summer
plans, and this year... maybe some unusual expectations.  In fact, this
year, the Perseid meteor shower may have something for everyone... activity
for Europe and Asia, activity for North America... and observing
opportunities for both the meteor neophyte and the hard core technical
observer!

The IMO, the International Meteor Organization, in their 2004 Meteor Shower
Calendar, talks about the history of outbursts observed:

"The Perseids were one of the most exciting and dynamic meteor showers
during the 1990s, with outbursts at a new primary maximum producing EZHRs
of 400+ in 1991 and 1992.  Rates from this peak decreased to 100-120 by the
late 1990s, and since 2000, it has failed to appear.  This was not
unexpected, as the outbursts and the primary maximum (which was not noticed
before 1988), were associated with particles accompanying the parent comet
109P/Swift-Tuttle passing perihelion in 1992.  The comet's orbital period is
about 130 years, so it is now receding back into the outer Solar System, and
theory predicts that such outburst rates should dwindle as the comet to
Earth distance increases."

Basically, when the comet is closer to the sun (and us), the earth
encounters more material shed by the comet, and we see more meteors.
However, this is a great oversimplification.  Why?  Because each time the
comet passes around the sun in its orbit, it sheds debris - and each of
these dust trails assumes its own orbit, slightly different from that of
the comet.  In time, we end up with a whole series of dust trails, each
trail in a slightly different orbit.  To an amateur meteor observer, this
means that different years can produce quite different numbers of
meteors seen.  To a professional meteor researcher, it means a computational
challenge!

So... what are the meteor researchers telling us about this year's Perseid
prospects?  We still have the regular annual Perseid activity...

In the IMO Calendar, the International Meteor Organization suggests that we
could get "a possible primary peak time around 11h UT on August 12...
coinciding with the most probable maximum time of the traditional peak...
Another feature, seen only in IMO data from 1997-1999, was a tertiary
peak... the repeat time for which would be shortly before 21h UT on August
12."  Note the times here.  UT, Universal Time, is the time at Greenwich,
England.  In other words, North America isn't dark at those times - so
Europe and Asia are favored.

The Perseids (PER) can be seen from about July 17th to August 24th.  The
radiant, the area in the sky where the meteors seem to come from, moves
quite a bit over this period of time though, so it is best to check a map to
see where the radiant is on a given night, before you go out observing.  A
map showing the radiant movement can be found on the IMO website at
http://www.imo.net/calendar/cal04.html#Perseids  Many beginning observers
think that the radiant is always just below the constellation Cassiopeia,
near the double star cluster h & chi - but such is not the case!

These are fast meteors, with a velocity of about 59 km per second, and can
be quite spectacular!  Quoted ZHR rates for the Perseids are about 100
meteors per hour.  ZHR refers to Zenithal Hourly Rate, and is the number of
meteors, on the average, that an observer would expect to see if they were
out under a dark country sky, and if the radiant of the shower is directly
overhead.

How about the other meteor researchers?  What do they say?  What is this
talk of a special outburst this year besides the regular 'annual' activity?
What is all this news about the 'one revolution dust trail', the debris shed
by Comet Swift-Tuttle in its pass by the inner solar system in 1862?

Researchers Esko Lyytinen and Tom Van Flandern discuss their predictions for
this year's Perseids in the April 2004 issue of WGN, the Journal of the
International Meteor Organization, in their paper 'Perseid one-revolution
outburst in 2004'.  Several selected excerpts are as follow:

"In 2004 August 11 at about 21h UT, the one-revolution dust trail of the
Perseids' parent comet 109P/Swift-Tuttle is calculated to pass within
0.0013 AU of the Earth's orbit... a possible meteor outburst of mostly
fainter-than-average meteors may be seen... with the optimum time occurring
at 20h 50m UT... with a maximum ZHR of a few hundred.  At best, activity
might approach meteor storm levels (1000/hour) for a short time...  we get
the predicted half-maximum full-width... about 40 minutes..."

"The trail has been calculated using similar principles as in the
Lyytinen-Van Flandern Leonids model...  We have the ejection at perihelion
and the ejection speed zero, as approximates the effect of solar tidal
forces removing debris orbiting a comet nucleus.  Radiation pressure is then
applied to model particles, starting from zero for the largest particles and
increasing in small steps for smaller particles.  With this approach we can
calculate where the center of the trail is situated... "

"We also discuss the possibility of enhanced annual rates because
perturbations by Jupiter will now direct all incoming Perseid meteoroids
about 0.01 AU closer to the Sun, which allows the possibility of the
Earth passing through the densest core of the annual stream...  If this
enhancement happens, it does not mean increased rates for the whole four
week time span when Perseids can be observed.  Only the main maximum may be
more prominent.  The maximum may also be shifted in time from the annual
peak or possibly appear as a peak distinct from the annual and the one
revolution peak... "

"Another factor is that the situation can be different in different
locations along the orbit.  There may be a denser younger core (filament
composed of several trails) that follows the parent comet for a number of
years but then gets more weak and indistinguishable before the next return.
This kind of encounter may be displaced from the annual maximum, more
probably being earlier in time.  This is also expected to be briefer than
the traditional maximum but wider than possible encounters of single
trails... "

Lyytinen comments, in his June 1st posting to the MeteorObs email list:

"The timing of the 1-rev. encounter is expected to be good within about 15
minutes or better.  The prediction of strength is more uncertain than the
timing... "

"... increased rates... during the annual peak... may be of more interest in
parts of the USA.  There may not be existing conclusive historic evidence on
the existence of ... this phenomenon that should repeat every 12 years (and
every 30 years because the effect of Saturn, next time in 2009)."

Lyytinen gives some very interesting ideas in his July 6th posting:

"If you do see visually quite a lot of dim meteors (during the outburst
time), testing telescopic observations (near the radiant) might give
something interesting...  Because the one revolution trail will pass a
little inside the Earth orbit, we can get a view tangentially to this trail.
There may be some possibility to observe the one revolution trail in
space... and this MAY be more dense that Leonids one revolution trail...
the most dense core may appear only some arc-minutes wide (or possibly even
smaller)...  CCD-equipment would best suit for this, but other photography
and visual sightings could be tried.  Because of the relatively small
apparent size of the densest part, no very wide field instrument is
recommended.  I expect equipment that are good for cometary observations to
be good for this purpose."

"I tried to derive the apparent location (of the tangential point of the
trail center) from orbital elements of the trail particles around there and
I got RA and dec (J 2000.0):  3h 39.0m, +84.86 deg.  This is valid at the
time of maximum of the outburst, that is expected to be the best time to get
the trail visible.  The movement is about half a degree in one hour.  An
hour before the maximum time, the location is 3h 36.2m 84.33 deg and an hour
after the maximum it is 3h 42.5m 85.40 deg.  I hope that I got this
correctly... "

Jeremie Vaubaillon of France has done some simulations on the 2004 Perseid
activity as well.  His simulations can be found on the web at
http://www.imcce.fr/s2p/PER.  Vaubaillon comments:

"Our first results gave indeed an intersection with the Earth... but without
that many particles.  So we decided to include tinier meteoroids...  We
still do not find a "Perseid storm"...  So maybe the 2004 Perseids <1862
trail> will be more detectable by radio devices (if their sensitivity is
better than optical devices).  The lack of model for the annual stream
prevents us from giving a clear idea of the expected enhancement...
However, we call for observers to be particularly vigilant between 11th and
12th August, and even before and after! "

Huan Meng of China has also given some predictions on the MeteorObs email
list, on July 16th:

"I have just completed my computation, and would like to let you know my
results.  Only 1-rev. trail was considered in my work.  Finally, I found
the whole dust trail has not been too much perturbed by giant planets.
In 2004, there will be only one cross section of the trail encountering the
earth in August...  the Perseid comet 109P is an order larger than the
Leonid comet 55P (diameter 15.6 km vs. 1.8 km), so the cometary nucleus may
eject dust grains farther...  However, I still expected this Perseid
outburst as a very faint one for visual observers.  More powerful observers
such as telescopic, video, radio and radar may better catch the outburst...
And the maximum time will be 20h 57m UT, August 11... "

Several other researchers in the U.S. and around the globe have made some
comments as well... but the above are the main sources of comment for this
year's Perseids, and are the sources we are quoting...  If you want to
follow some of the discussions on the Perseids, and hear about the results
around the globe - consider subscribing to the MeteorObs email list,
administered by Lew Gramer, our Coordinator of Public Outreach.  Check out
the details for MeteorObs at http://www.meteorobs.org

This is shaping up to be an interesting year for the Perseid meteor
shower!  Beginning observers can sit back and enjoy the best shower of the
summer.  Experienced visual observers have some interesting data to record.
The technical gurus have some even more challenging results to capture by
CCD, video and other means.  It will be interesting to see what results are
obtained - and great to further our knowledge of this shower!

As a reminder to visual observers, our NAMN Observing Guide provides
information on what to record while observing.  Check it out at
http://www.namnmeteors.org/guide.html
The information to record includes such items as the time the meteor
occurred, its magnitude (brightness), the shower it belongs to, its speed,
and other comments such as train left behind, or color.  General information
to record includes such things as how dark your perceived sky is (limiting
magnitude), and comments on weather and cloud cover.

Forms to record your observations can be found at
http://www.namnmeteors.org/namn_form.html and
http://www.namnmeteors.org/appendixC.html.  Questions on what to record, or
how, can be sent to our NAMN Coordinator at meteors at comcast.net


2.  Aquarids and More Aquarids Again...

Our August skies continue to be full of Aquarid meteors.  We have 4
different Aquarid showers active this month - the north and south delta
Aquarids, and the north and south iota Aquarids.  It is a challenge keeping
track of them all!

The southern delta Aquarids (SDA) reached a peak on July 27th, but can be
seen until about August 19th.  These are average velocity meteors, at about
41 km per second.  ZHR rates at the peak were about 20 meteors per hour.
Rates in August will be lower.

The southern iota Aquarids (SIA) reach a maximum on August 4th, and run
until about August 15th.  These are slower than the delta Aquarids, with a
velocity of about 34 km per second, but still classed as 'average' velocity.
At maximum on the 4th, the ZHR rate will be about 2 meteors per hour.

The northern delta Aquarids (NDA) reach a peak on August 8th, and can be
seen until about August 25th.  These are average velocity meteors at about
42 km per second, very similar to the southern delta's.  On August 8th, they
will reach a ZHR of about 4 meteors per hour.

The northern iota Aquarids (NIA) peak on August 19th, but can be seen from
about August 11th to 31st.  These are average velocity meteors at about 31
km per second, very similar to the southern iota's.  On August 19th, they
will reach a ZHR of about 3 meteors per hour.  According to the IMO, the
International Meteor Organization, the peak could happen several days after
the suspected peak time.

These all seem like low rates - but add them all together, and they make up
a fair number of the meteors you will see on a summer night!

Where do they seem to come from, and how do you keep track of them?  On the
IMO website, there is a map showing the movement of all 4 of these radiants
over the month.  Not only are there 4 showers with radiants fairly close in
the sky, but all 4 radiants move a bit from night to night.  Check out the
map at http://www.imo.net/calendar/cal04.html#Aquarids

There is a fairly easy way to keep track of these 4 showers.  Print yourself
off a copy of our NAMN star charts (set printer to 'landscape' mode):
http://www.namnmeteors.org/charts.html.  Before you go out observing, mark
the Aquarid radiants for that night on your map.  You will see that the 4
radiants roughly form a sort of parallelogram shape in the sky.  And - face
that general area of the sky when you are observing if you hope to be able
to tell the showers apart.  If Aquarius is behind you, and you are not
plotting, you will not be able to differentiate between these showers.  If
you are a new observer, and not experienced, it is suggested that you just
treat these meteors as 'Aquarids'.


3.  Other August Meteor Activity...

The August summer sky is really a very busy place.  Not only do we have
Perseids and 4 different Aquarid showers active, but there is more!

The Pisces Austrinids (PAU) reached a maximum on July 27th, but can be seen
until about August 10th.  These are average velocity meteors at about 35 km
per second.  The radiant at maximum was at 341 degrees, ie. RA 22h 43.8m,
Dec -30, which was about 3 degrees to the right of alpha Pisces Austrinus,
the star known as Fomalhaut.  For a map showing the radiant positions in
August, check out the IMO Meteor Shower Calendar at:
http://www.imo.net/calendar/cal04.html#Aquarids.  ZHR rates at maximum were
about 5 meteors per hour.  Rates in August will be lower.

The alpha Capricornids (CAP) reached a maximum on July 29th, but last until
about August 15th.  These are wonderful, slow meteors, with a velocity of
about 23 km per second.  The radiant at maximum was at 307 degrees, ie. RA
20h 28.2m, Dec -10, which was about 4 degrees up to the left of the star
alpha Capricornus, the top right star of the triangle of Capricornus.  For a
map showing the radiant positions in August, check out the IMO website at
http://www.imo.net/calendar/cal04.html#Aquarids.  ZHR rates at maximum were
about 4 meteors per hour, with lower rates in August.

The kappa Cygnids (KCG) peak on August 17th, and can be seen from about
August 3rd to 25th.  These are slow meteors, at about 25 km per second, so
will be a bit easier to pick out from all the other August meteor activity.
The radiant at the peak will be at 286 degrees, ie. RA 19h 4.2m, Dec +59,
which is about 2 degrees up to the right of the star 54 Draco.  For a map
showing the movement of the radiant throughout August, check out
http://www.imo.net/calendar/cal04.html#kappa-Cygnids.  ZHR rates at maximum
will be about 3 meteors per hour.  The IMO mentions that occasional slow
fireballs have been reported from this shower - so stay alert!  Observations
are requested!

Lastly, the alpha Aurigids (AUR) reach a maximum on August 31st at about 18h
UT, although run from about August 25th to September 8th.  These are fast
meteors, at about 66 km per second.  The radiant at maximum will be at 084
degrees, ie. RA 5h 36m, Dec +42, which is about 5 degrees to the left of the
star eta Auriga, the star known as Hoedus II, 'the Charioteer's 2nd kid
goat'.  A map of the radiant can be found at
http://www.imo.net/calendar/cal04.html#delta-Aurigids.  ZHR rates at the
peak will be about 7 meteors per hour.  Outbursts of this shower have
occurred in the past - so please monitor this shower!

And - besides all these main showers, and other minor activity, there is
also sporadic meteor activity in August - about 7 meteors per hour, visible
to the unaided eye.  Some of these are random, and some belong to old
untraceable meteor showers.  Add all this activity together, and you will
appreciate just how active the summer sky can be!

More information on minor showers can be found on Gary Kronk's 'Comets and
Meteor Showers' website at http://comets.amsmeteors.org

For observers interested in radio meteor showers, more details can be found
on the website of the IMO, the International Meteor Organization, at
http://www.imo.net.  The gamma Leonids are active from about August 14th to
September 12th, with a peak on August 25th at 3h UT.

Planets at midmonth, and their magnitudes, for northern observers, are:

Venus      -4.3   very low in east-northeast in morning sky
Jupiter    -1.7   in Leo, very low in west in evening sky
Saturn      0.2   in Gemini, low in east-northeast in morning sky

Actually, around the time of the Perseid peak, the morning sky will be quite
pretty.  On August 11th, Venus will be about 8 degrees south of the moon.
On August 13th, Saturn will be about 5 degrees south of the moon.  To see
where the planets are in your sky in the month of August, check out the
website 'Heavens Above' at http://www.heavens-above.com

This month, the phases of the moon are as follows:
Sat. Aug.  7    last quarter
Mon. Aug. 16    new moon
Mon. Aug. 23    first quarter
Mon. Aug. 30    full moon
For a great printout of moon phases for the month, check out
http://stardate.org/nightsky/moon


4. Upcoming Meetings...

August 2-6, 2004, Rio de Janeiro, Brazil...
Note:  All of the abstracts for this conference can now be read online at:
http://www.lpi.usra.edu/meetings/metsoc2004/pdf/program.pdf

The 67th Annual Meeting of the Meteoritical Society will be held in Rio de
Janeiro, Brazil, and hosted by the Brazilian Center for Physics Research.
Topics covered will include various meteorite studies, carbonaceous and
other types of chondrites, martian meteorites, micrometeorites and IDP's,
impact processes and structures, asteroids and comets, and early solar
system chronology. Special sessions will cover current missions and future
sample returns, presolar grains, and South American impact structures.
Post-conference tours will include the Araguainha Crater and other sites of
interest.  Student travel grants are available.  For more information,
contact the Conference Chair, Rosa B. Scorzelli at metsoc2004 at cbpf.br, and
check out the conference website at
http://www.lpi.usra.edu/meetings/metsoc2004/home.html

August 16-21, 2004, London, Ontario, Canada...
Note:  The program for this conference has now been posted online at
http://aquarid.physics.uwo.ca/meteoroids2004/program.html

Meteoroids 2004 will be held in eastern Canada, at the University of Western
Ontario in London. Experimental and observational methods discussed will
include optical observations of meteors including ground-based visual,
photographic, video, and telescopic techniques, satellite observations of
meteors in various passbands, measurements of meteoric atoms in the
atmosphere by lidars and other techniques, acoustic measurements using
infrasound and seismic detection techniques, radio detection of meteors
including VLF and ELF, meteor and large aperture radar observations, and
observations, in-situ satellite and laboratory measurements of dust and
meteorite material. Scientific areas discussed will include such topics as
dynamics of sporadic, shower and interstellar meteoroids, physics and
chemistry of meteoroids and their interaction processes in the atmosphere,
fireball and bolide phenomenology, mineralogy of extraterrestrial materials,
hypervelocity impacts on spacecraft, meteoroid models and flux, and
interrelation of meteoroids, meteorites, IDP's, asteroids and comets.
The website for the conference is at http://www.uwo.ca/meteoroids2004

September 23-26, 2004, Varna, Bulgaria...
The IMC, the International Meteor Conference of the International Meteor
Organization, is being held this year in Varna, Bulgaria.  Varna is often
called the 'sea capital' of Bulgaria due to its location on the Black Sea.
The conference will be held at the Chayka resort, about 10 km outside the
city, and participants housed at the Varna Free University.  The IMC is the
worldwide meeting for meteor observers - both amateurs and professionals
alike.  It is a great opportunity to meet observers from around the globe
and learn about research and projects being carried out.  Details on
registration can be found on the IMO website at http://www.imo.net.  For
email queries, contact Eva Bojurova or Valentin Velkov at
planetarium at triada.bg

For more information on upcoming astronomy meetings, see: "International
Astronomy Meetings List" at http://cadcwww.hia.nrc.ca/meetings


5. For more info...

NAMN email:  namn at namnmeteors.org
NAMN website: http://www.namnmeteors.org

Mark Davis, meteors at comcast.net
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network

Cathy Hall, chall at cyberus.ca
Metcalfe, Ontario, Canada
Writer, NAMN Notes

Lew Gramer, dedalus at alum.mit.edu
Medford, Massachusetts, USA
Coordinator, Public Outreach
Owner/Moderator, 'MeteorObs'

Kevin Kilkenny, namnfireball at earthlink.net
Staten Island, New York, USA
Coordinator, Fireballs and Meteorites

Back issues of NAMN Notes can be found online at the NAMN website and in
the MeteorObs archives at:
http://www.meteorobs.org by selecting 'Browse Archive by Month'

To subscribe to the meteor email list:
Contact Lew Gramer at: dedalus at alum.mit.edu

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Here's to 'Clear Skies' for August...

August 2004 NAMN Notes
written by Cathy Hall & edited by Mark Davis
==============================================