(meteorobs) NAMN Notes: August 2007

Wed Jul 25 17:54:09 EDT 2007

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NAMN Notes:  August 2007
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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 - Highlight of the Summer...
2.  Other Summer Meteor Activity...
3.  Upcoming Meetings...
4.  For more info...

1.  Perseids - Highlight of the Summer...

The Perseid meteor shower (PER) is the highlight of the summer meteor
season.  This year's shower is also very favorable - as it occurs very close
to both new moon and a weekend.

The Perseids are one of the oldest meteor showers that mankind has records
for.  The earliest reference to the shower seems to have been in the year 36
A.D. in China.  Because the path of the Perseids is highly inclined to the
ecliptic, it has not been affected as much over the millennia by the
disturbing influences of our major planets that travel basically along the
ecliptic path.  As a result, the Perseids are a reliable meteor shower, seen
in strength each year.

The Perseids were also the first meteor shower to be proven to be associated
with a comet.  This was found by Giovanni Virginio Schiaparelli (1835-1910),
more often remembered for giving the name canals or channels to the markings
on the planet Mars.  The parent body of the Perseid shower is called Comet
109P/Swift-Tuttle after its discovery in 1862 by several Americans - Lewis
Swift of Marathon, New York and Horace Tuttle of Harvard Observatory,
Massachusetts.  In late August and early September of that year, the comet
reached a magnitude of about 2, about as bright as the stars in the Big
Dipper, and it had a tail length of between 25 and 30 degrees, about 5-6
times the distance between the pointer stars of the Big Dipper.

In early Europe, the Perseids came to be known as the "tears of St.
Lawrence".  In an article called 'The Discovery of the Perseid Meteors' on
the Sky and Telescope website at http://www.skyandtelescope.com, Mark
Littmann wrote:

"Saint Lawrence was tortured and killed in Rome on August 10, 258 during the
reign of the anti-Christian emperor Valerian... Citing Quetelet, 'a
superstition has 'for ages' existed among the Catholics of some parts of
England and Germany that the burning tears of St. Lawrence are seen in the
sky on the night of the 10th of August; this day being the anniversary of
his martyrdom.' "

When can the meteors be seen?  The Perseids started to become active back
about July 17th, and reach a peak around August 13th.  After that, they can
still be seen, although in lesser numbers, up to about August 24th.

Where should an observer look in the sky?  Perseids can be seen anywhere in
the sky, but if you trace their path backwards, they will appear to come
from an area near the constellation of Perseus.  A map of the radiant can be
found at http://www.imo.net/calendar/2007.  The radiant moves over time -
the Perseids seen back in July came from a slightly different area in the
sky compared to the Perseids that we will see in August.

How many meteors do we expect to see?  At the peak, around August 13th, the
ZHR rate will be about 100 meteors per hour.  What is ZHR?  This refers to
Zenithal Hourly Rate, and is the number of meteors that an observer would
expect to see in an hour, on average, if they are out observing under
dark skies and if the radiant, the area in the sky where the meteors seem
to come from, is directly overhead.  This year, we have new moon - which
means darker skies, and more meteors easily visible.  Beginners should note
that these meteor rates are for the unaided eye - all you need is a
comfortable reclining chair and your eyes!

Is there a preferred time to observe the meteors?  According to the
International Meteor Organization (IMO), the main activity should occur on
Monday August 13th, between 5h UT and 7h30m UT, Universal Time in Greenwich,
England.  For eastern North American observers on EDT (subtracting 4 hours),
this means August 13th between 1 a.m. and 3.30 a.m..  However, the IMO says
that we may also see possible activity from the 'old' primary peak around
9h UT on the 13th, ie. about 5 a.m..  And - there may be another time
of lesser enhanced activity at 15h UT on the 13th, ie. about 11 a.m.
(daylight in North America).  It should be noted though, that meteor
activity will be high for several days before and after the 13th.  The
weekend of the 11th and 12th will be prime time for many observers.

What do Perseids look like?  Perseids are fast meteors with a velocity of
about 59 km per second.

The magnitude or brightness of the meteors themselves is interesting as
well.  Studies by Hruska and Ceplecha in the 1950's indicated that the
Perseids generally seem to be brighter before the date of maximum activity
than afterwards, but that some periods of brighter or fainter meteors do
occur.  This tends to indicate some filamentary structure in the Perseid
meteoroid stream.  In other words, we encounter clumps of brighter or
fainter meteors as the earth passes through different layers of long-ago
debris shed by Comet Swift-Tuttle.

Legends abound about Perseus.  In ancient Greek mythology, he was a hero -
the son of Zeus.  On one quest, he took off to slay the famed Medusa, a
beautiful mortal lady who had been unceremoniously turned into a fearsome
Gorgon by the jealous goddess Athena.  Medusa's beautiful hair became a
squirming mass of snakes - and her gaze deadly.  Perseus traveled with the
help of winged sandals from Hermes, the messenger god; a sword of diamond
from Hephaestus, the god of fire and the forge; and a magical helmet to make
him invisible, from Hades, god of the underworld.  He slew Medusa without
looking at her by using her reflection in his shield.  The blood of Medusa
fell to earth and created the great winged horse Pegasus.

On his way home, he rescued the princess Andromeda, daughter of King
Cepheus, who was chained to a rock as a sacrifice to the sea monster Cetus
because of the vainful boasting of her mother, Queen Cassiopeia.  Perseus
rescued the fair maiden and married her.  And now, in our constellations, we
have all the players in the legend.  Take a look at your sky.  We have
Perseus, Pegasus, Andromeda, Cepheus, Cassiopeia, and Cetus - and even the
infamous Medusa, immortalized as the 'Demon Star' in the constellation of
Perseus.

For some great sky maps showing not only the stars, but the ancient
mythical drawings superimposed, check out Jan Wisniewski's website at
http://www.astrosurf.com/jwisn/constellations.htm

If you want to help record visual data for the meteor researchers,
check out our NAMN Observing Guide for information on what to record.  Our
Guide can be found at http://www.namnmeteors.org/guide.html.  We record such
info as the time a 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.  If you have any questions, drop a note to the NAMN Coordinator at
meteors at comcast.net

For visual observers, NAMN has a set of 4 star charts to help you judge the
brightness (magnitude) of the meteors you see.  They are also a great tool
for new observers to help you learn your constellations better.  The charts
can be printed off from http://www.namnmeteors.org/charts.html.  Set your
printer to landscape mode.

Forms to record your observations can be found at
http://www.namnmeteors.org/namn_form.html and
http://www.namnmeteors.org/appendixC.html

2.  Other Summer Meteor Activity...

There are a number of other meteor showers active in August.  These are not
as spectacular as the Perseids, but can be very rewarding to observe, and
can hold some surprises.

The Pisces Austrinids (PAU) peaked back on July 28th, but can be seen until
about August 10th.  These are average velocity meteors at about 35 km per
second.  ZHR rates at the peak were about 5 meteors per hour, but rates in
August will be less.  For a map of the radiant, check out
http://www.imo.net/calendar/2006/summer

The southern delta Aquarids (SDA) also peaked on July 28th, but can be seen
until about August 19th.  These are average velocity, at about 41 km per
second.  This shower is rich in faint meteors, but also has brighter meteors
as well.  ZHR rates at the peak were about 20 meteors per hour, but rates in
August will be much lower.  The radiant can be seen at
http://www.imo.net/calendar/2007

The alpha Capricornids (CAP) peaked about July 30th, and run until about
August 15th.  These are wonderful, slow meteors, with a velocity of about 23
km per second - and are quite distinctive when you see them.  ZHR rates at
the end of July were about 4 meteors per hour.  Rates in August will be low,
but observers will be delighted when they see one of these meteors.  A map
of the radiant can be found at http://www.imo.net/calendar/2007.  According
to the IMO in their annual Meteor Shower Calendar, the alpha Capricornids
"are noted for their bright - at times fireball-class - events, which,
combined with their low apparent velocity, can make some of these objects
among the most impressive and attractive an observer could wish for."

The kappa Cygnids (KCG) reach a maximum on August 18th and can be seen from
about August 3rd to 25th.  These are almost slow meteors at about 25 km per
second.  ZHR rates at the peak will be about 3 meteors per hour.  A map of
the radiant can be found at http://www.imo.net/calendar/2007.  The IMO
mentions that "occasional slow fireballs from this source have been
reported... more data are needed on a shower that is often ignored in favour
of the major Perseids during August."

Lastly, the alpha Aurigids (AUR) start to become active about August 25th,
although will not peak until September 1st.  These are fast meteors at 66 km
per second.  ZHR rates at the peak will reach about 7 meteors per hour, but
rates in August will be lower.  Where is the radiant?  Check out
http://www.imo.net/calendar/2007.  This shower had short unexpected
outbursts of about 30-40 meteors per hour in 1935, 1986 and 1994.

The Antihelion Source (ANT), the ecliptical activity, produces a ZHR of
about 3 meteors per hour, with an average velocity of about 30 km per
second.  A map showing the movement of the radiant throughout the month can
be found at http://www.imo.net/calendar/2007

For other August minor showers not on the International Meteor
Organization's 'Working List of Visual Meteor Showers', and for a wealth of
historical information on all showers, check out Gary Kronk's 'Meteor
Showers Online' website at http://meteorshowersonline.com

Besides August's main activity, and other minor showers, there is also
sporadic meteor activity.  This sporadic meteor activity is about 7 meteors
per hour visible to the unaided eye.  Some of these are random and some
belong to old untraceable meteor showers.

For those of you interested in plotting your meteors (recommended for
serious observations), special IMO plotting maps can be ordered through
Robert Lunsford of the International Meteor Organization. For details,
contact him directly at lunro.imo.usa at cox.net

The magnitudes of the planets just before mid-month are as follows:
Jupiter     -2.3
Mars         0.5

For a sky chart showing the positions of these planets in August,
go to http://www.heavens-above.com, 'Select' your country, type in the name
of your nearest city, and then go to 'Whole Sky Chart'.  Pick 'black on
white' before printing.  The 'Heavens Above' website will also tell you when
to look to see the ISS, the International Space Station, go over your
observing site.

The phases of the moon for August are as follows:
Sun.  Aug.  5   last quarter
Sun.  Aug. 12   new moon
Mon.  Aug. 20   first quarter
Tues. Aug. 28   full moon (total lunar eclipse)

For phases of the moon, a great monthly moon calendar can be printed off
from http://stardate.org/nightsky/moon.  For the NASA kids' calendar for
August, go to http://spaceplace.nasa.gov/en/kids/calendar.shtml

For up to date info on what's happening in the sky right now, check out
'SpaceWeather' at http://www.spaceweather.com

3.  Upcoming Meetings...

August 9-13, 2007, Mount Forest, Ontario, Canada...

Starfest 2007, Canada's largest amateur astronomical observing convention,
will be held at the River Place Campground, near Mount Forest, Ontario.
This year's theme is 'The Universe in Motion' - and covers many different
fields of astronomy.  There will be a panel discussion on 'McNaught:  The
'Tail' of a Great Comet', chaired by well-known astronomy writer Terence
Dickinson.  On meteors, there will be a talk by Dr. Peter Brown of the
University of Western Ontario Meteor Physics Group on the 'Southern Ontario
Meteor Network'.  Details on all the many speakers, and convention info, can
be found online at http://www.nyaa-starfest.com

August 13-17, 2007, Tucson, Arizona, U.S.A...

The 70th Annual Meeting of the Meteoritical Society will be held in Tucson,
Arizona.  Special sessions will be held on meteor craters and impacts,
chondrules and chondrule formation, protoplanetary dust, and the study of
cosmogenic radionuclides, with other sessions on meteorites, asteroids and
comets, and high and low temperature parent body processes.  A 3-day
post-conference field trip will be held to the Barringer Meteorite Crater,
Sunset Crater Volcanic National Monument, and the Grand Canyon.  For
information, contact Elizabeth Wagganer of the Lunar and Planetary Institute
at wagganer at lpi.usra.edu and check out the conference website at
http://www.lpi.usra.edu/meetings/metsoc2007

Note:  check out the online abstracts for the conference at
http://www.lpi.usra.edu/meetings/metsoc2007/metsoc2007.authorindex.shtml.
Click on the 4-digit code to read the ones that interest you...

September 6-9, 2007, Ivy, Ontario, Canada...

HSP 2007, the Huronia Star Party, a small but growing amateur astronomical
gathering, will be held about an hour's drive north of Toronto, Ontario, at
Camp Saulaine.  Dr. Peter Brown of the University of Western Ontario Meteor
Physics Group will give several talks - 'Impacts of Large Bolides as
Observed by Earth Orbiting Satellite and Infrasound Networks' and 'The Fall
and Recovery of the Tagish Lake Meteorite'.  Details on the other speakers,
and on this casual but informative astronomical gathering, can be found at
http://www.cois.on.ca/~ssaa

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

If you know of other astronomical meetings where talks on meteors will be
given, please drop a note to our NAMN Coordinator and let us know!

4.  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
Ottawa, Ontario, Canada
Writer, NAMN Notes

Lew Gramer, dedalus at alum.mit.edu
Homestead, Florida, 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 2007 NAMN Notes
written by Cathy Hall & edited by Mark Davis
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