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(meteorobs) NAMN Notes: August 2002
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NAMN Notes: August 2002
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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 - The Great Summer Meteor Shower...
2. The Aquarid Blitz Continues...
3. Other Meteor Showers of August...
4. Upcoming Meetings...
5. For more info...
1. Perseids - The Great Summer Meteor Shower...
In his book 'Popular Astronomy', first published in 1879, the French
astronomer Camille Flammarion writes:
"In the clear and transparent night a distant star seems to detach itself
from the heavens, glide in silence on the nocturnal vault, shoot along, and
disappear. The heart tried by terrestrial sorrows believes that the heavens
are concerned with our destinies, and that the shooting star marks the
departure of a spirit to another life; the young girl whose pensive gaze is
attracted for a moment to the meteor hastens to form a wish, with the hope
of seeing it speedily granted; the poet dreams that the stars, the flowers
of the sky, bloom in the celestial fields, and thinks he sees their luminous
petals swept away by upper winds through the infinite night; the astronomer
knows that this ephemeral body is neither a star nor a spirit, but a
molecule, a cosmical atom, a fragment more or less minute itself, but of
which the lesson may be great, if we can learn whence it comes and how it
thus encounters the earth in its course."
Meteors have fascinated people for thousands of years. Some of us take a
poetic approach to these delightful flashes of light in the sky, and others
of us are also fascinated by studying these bits of (usually) comet debris
that hit our earth's upper atmosphere, burn up due to friction, and emit the
light events we call meteors.
One of the most famous of all meteor showers occurs in August every year.
Meteor showers don't last forever though. The comets that usually spawn
the debris that we encounter will eventually run out of material to shed.
Or, the comet or its already shed filaments of debris may become perturbed
in their orbits by planetary bodies - and sometime in the future - our earth
may no longer pass through that debris. Meteors as such are transient
phenomena in more ways than one!
The Perseids (PER) have been observed for several thousand years now. This
is one of the oldest meteor showers that we have records of. The earliest
reference to them seems to have been in the year 36 AD in China. Because
the path of the Perseids is highly inclined to the ecliptic, it has not been
affected as much over the millenia 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 has
since been 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. It must have been an impressive sight!
This year, the Perseids reach maximum activity on August 12, and at that
time will seem to radiate from an area of the sky situated at 046
degrees, ie. RA 3h 4.2m, Dec +58, about a degree north of the star kappa
Perseus. Perseids can be seen from about July 17th until about August 24th
though - and the radiant actually moves quite a distance over that time
period - from below the constellation of Cassiopeia over to the upper part
of Perseus. To see a map of the movement of the radiant area, take a look
at the map on the website of the International Meteor Organization (IMO)
at http://www.imodot net/calendar/cal02.html#Perseids
August 12th is the quoted date of maximum - but this year we could see
several times of enhanced activity. According to the 'IMO Meteor Shower
Calendar 2002', the times of particular interest to watch are as follows:
August 12 20.15 UT, possible feature
August 12 22.30 UT, normal 'peak' time
August 13 08.30 UT, possible feature
This is UT, Universal Time, time at Greenwich, England. For observers on
the east coast of North America on EDT, Eastern Daylight Time, these times
become:
August 12 16.15 EDT, ie. 4.15 pm in the afternoon, possible feature
August 12 18.30 EDT, ie. 6.30 pm in the evening, normal 'peak' time
August 13 04.30 EDT, ie. 4.30 am in the morning, possible feature
For observers elsewhere, you will have to adjust your time accordingly.
The Zenithal Hourly Rate (ZHR) for the Perseids is about 110 meteors per
hour, for the normal peak time. This is the number of meteors, on
average, that an observer would expect to see if they are out under a dark
country sky, and if the radiant, the area in the sky where the meteors
seem to come from, is directly overhead. However, meteor shower rates do
change over time. Rates for the Perseids were higher when the parent comet
was in our neighborhood back in 1992. Now that the comet is heading back
to the outer solar system, outburst rates will decline. Observations on all
nights are useful so that the meteor researchers can get a good profile of
Perseid activity, so even if you get clouded out on a couple nights, your
observations on other nights are still very welcome!
Perseids are generally bright, with an average magnitude of about 2.3
according to Gary Kronk, on his authoritative website 'Comets and Meteor
Showers'. This is roughly the brightness of the stars in the Big Dipper. A
large percentage of Perseids have persistent trains - as many as 45% of all
Perseids, by some accounts. Their brightness and their trains left behind
make them beautiful meteors to witness. The average brightness of the
meteors can also be seen to change from night to night, as the comet debris
that causes the meteors has been sorted by particle size over time.
Perseids are fast meteors, with a velocity of about 59 km per second.
Kronk's comments can be found at http://comets.amsmeteors.org
For those of you interested in doing some serious observations of the
Perseids, using a notepad or tape recorder and an accurately set watch, our
NAMN Observing Guide gives details on what you should record - such as time
of meteor, its brightness, shower identification, estimation of velocity,
and length of train. The Guide can be found at
http://www.namnmeteors.org/guide.html and forms to use in recording (or
decoding from a tape) can be found at
http://www.namnmeteors.org/reports.html
For some good constellation maps - with standard stars marked on to judge
the brightness of the meteors you see - set your printer to 'landscape' mode
and print off a set of our 4 NAMN maps at
http://www.namnmeteors.org/charts.html
If you want to try photographing meteors with a camera, the Perseids are the
best shower of the year to do this for! (And, with the Leonids predicted to
reach storm levels in November, the Perseids are excellent practice.)
What equipment do you need? Use a tripod, a camera with a bulb (time
exposure) setting, fast film (ASA 400 or higher), a lens wide open (or close
to it), and exposures of about 10-15 minutes each depending on how bright
your sky background is. Most serious meteor photographers use black and
white film - but color film is very popular too, especially for those who
are mainly interested in photography as opposed to just meteors. If you
have a telescope with a drive system, try piggybacking your camera on the
telescope to keep the stars from trailing in your photos. A regular lens,
or wide angle lens, is the best to use to capture a good expanse of sky.
Lastly, always put a normal looking photo of some kind at each end of the
roll, so the processing lab knows where to (and where not to) cut.
We are fortunate to have dark skies for the Perseid meteor display this
year - so take some time to relax, and enjoy a great show! Whether you are
into scientific recording of meteor data, or into a poetic appreciation of
the night sky - the Perseids are a wonder and a delight.
As Flammarion wrote in his 'Astronomy for Women' about 1903:
"What greater delight can be conceived... at the hour when the crescent moon
is shining in the west amid the last glimmer of twilight, than the
contemplation of that grand and silent spectacle of the stars stepping forth
in sequence in the vast heavens? All sounds of life die out upon the earth,
the last notes of the sleepy birds have sunk away, the Angelus of the church
hard by has run the close of day. But if life sleeps around us, we may seek
it in the heavens... The darkness is profound, the abyss immense... See!
Yonder a shooting star glides silently across the sky, and disappears!..."
2. The Aquarid Blitz Continues....
August is prime Aquarid observing - and we have 4 different Aquarid meteor
showers that serious observers record data on! For casual observers, you
have a wonderful display of meteors from the constellation of Aquarius, the
Water Bearer. Check out information on this interesting constellation at
http://www.hawastsoc.org/deepsky/index.html
For experienced observers, the 4 Aquarid radiants are not really that hard
to keep track of in the sky. They usually form a parallelogram pattern once
you plot them on your star map, so you just have to remember which corner is
which shower radiant. Our NAMN star maps are ideal for this, and are
available at http://www.namnmeteors.org/charts.html
The northern delta Aquarids (NDA) reach a maximum on August 8th, but can be
seen until about August 25th. These are average velocity, at about 42 km
per second. At maximum, ZHR rates will be about 4 meteors per hour, and the
radiant will be at 335 degrees, ie. RA 22h 19.8m, Dec -05, which is about 4
degrees south of the star gamma Aquarius.
The southern delta Aquarids (SDA) reached a maximum back on July 28th, but
can be seen until about August 19th. These are average velocity at about
41 km per second. On Saturday August 10th, near new moon, the radiant will
be at 349 degrees, ie. RA 23h 16.2m, Dec -13, which is about 3 degrees north
of the star phi Aquarius. ZHR rates at maximum in July were about 20
meteors per hour, but in August will be low.
The northern iota Aquarids (NIA) reach a maximum on August 20th, but can be
seen until the end of the month. These are almost slow meteors, at about 31
km per second. At maximum, ZHR rates will be about 3 meteors per hour and
the radiant will be at 327 degrees, ie. RA 21h 48m, Dec -06, which is about
4 degrees to the left of the star beta Aquarius, the star called Sadalsuud,
translated as 'luckiest of the lucky'.
The southern iota Aquarids (SIA) reach a maximum on August 4th, but can be
seen until about August 15th. These are almost slow meteors, at about 34 km
per second. At maximum, ZHR rates will be about 2 meteors per hour, and the
radiant will be at 334 degrees, ie. RA 22h 16.2m, Dec -15, which is about 6
degrees off to the left of the star delta Capricornus, the top left star of
the triangle of Capricornus.
According to the International Meteor Organization, talking about the delta
and iota Aquarid meteor streams in their 2002 calendar:
"Neither shower has been closely studied in recent years, and any reliable
data would be very useful... The July-August Aquarid showers are all rich
in faint meteors, making them well-suited to telescopic work, although
enough brighter members exist, especially in the delta-Aquarids, to make
visual and photographic observations worth the effort too, primarily from
more southerly sites. Such a concentration of radiants in a small area of
sky means that familiarity with where they are is essential for accurate
shower association for all observing nights. Visual watchers in particular
should plot every potential stream member seen in this region of sky rather
than trying to make shower associations in the field."
and, in their IMO Handbook, recommend:
"If you do not plot the meteors and/or do not watch a field in the immediate
vicinity of the radiants, it is not practical to be able to distinguish
between the different Aquarid radiants. Instead you should simply count all
these meteors as 'Aquarids'."
A map showing all the various Aquarid radiants - and their movement over the
month from night to night - can be found at
http://www.imodot net/calendar/cal02.html#Aquarids
Regardless of whether you are observing these Aquarid meteor showers
seriously, or just for casual summer enjoyment, these average and slower
meteors make an interesting addition to all the fast Perseid activity this
month!
3. Other Meteor Showers of August...
The Pisces Austrinids (PAU), although having reached a maximum back on July
27th, can be seen until about August 10th. ZHR rates in July were about 5
meteors per hour, but in August will be low. These are average velocity
meteors, at about 35 km per second. On August 10th, near new moon, the
radiant will be at 352 degrees, ie. RA 23h 28.2m, Dec -26, which is about 7
degrees up to the right of alpha Pisces Austrinus, the star called
Fomalhaut. On a historical note, this shower was discovered by Herschel on
July 28th, 1865.
The alpha Capricornids (CAP), although having reached a maximum on July
29th, can be seen also into August until about the 15th. These are
wonderful, slow meteors, with a velocity of about 25 km per second. They
are spectacular to see! ZHR rates will be low, as even at maximum rates
only reached about 4 meteors per hour. On the August 10th weekend, the
radiant will be at 318 degrees, ie. RA 21h 12m, Dec -6, which is about 5
degrees off to the right of beta Aquarius, the star Sadalsuud. This shower
often produces fireballs, and many of the meteors have been reported as
being yellow in color. The alpha Capricornids are believed to have a parent
body of either the asteroid (2101) Adonis or the comet
45P/Honda-Mrkos-Pajdusakova.
The kappa Cygnids (KCG) reach maximum activity on August 17th, and can be
seen from about August 3rd to 25th. These are also slow meteors with a
velocity of about 25 km per second. On August 17th, ZHR rates should reach
about 3 meteors per hour coming from a radiant at 286 degrees, ie. RA 19h
4.2m, Dec +59, which is not in Cygnus at all but about 2 degrees up to the
right of the star 54 Draco. This makes a nice equilateral triangle with the
bright stars Deneb and Vega. Many of these meteors have been described as
blue-white in color. Most of the meteors are medium bright to faint.
According to the International Meteor Organization, "occasional slow
fireballs from this source have been reported... There has been some
suggestion of a variation in its activity at times, perhaps coupled with a
periodicity in fireball sightings, but more data are urgently needed on a
shower that is often ignored in favor of the Perseids during August".
Lastly, the alpha Aurigids (AUR) reach a maximum on August 31st, although
can be seen starting about August 25th. These are fast meteors at about 66
km per second. At maximum, ZHR rates should reach about 10 meteors per
hour with a radiant 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'.
Besides recognized main showers and other minor showers, there is also
sporadic meteor activity in August. This sporadic activity is about 7
meteors per hour visible to the unaided eye. This activity is comprised
partly of random meteors and partly of meteors that belong to long-ago, now
untraceable showers.
NAMN, our North American Meteor Network, uses the International
Meteor Organization, 'Working List of Visual Meteor Showers'. These are all
showers visible to the unaided eye. If you want to do some reading on minor
showers not on this list, check out Gary Kronk's 'Comets and Meteor Showers'
website at http://comets.amsmeteors.org
If you would like to try plotting meteors this summer, special maps are
available, with a gnomonic projection which allows you to plot meteors as
straight lines - and allows the meteor researchers at the IMO to easily
enter all your plots into their worldwide database! These special plotting
maps are available at $4 US a set, from Mr. Robert Lunsford, IMO
Secretary-General, at 161 Vance Street, Chula Vista, California 91910, USA.
There are 12 maps in the set - you can keep the originals as a master set,
and make yourself copies for your observing sessions. Plotting is an
interesting activity - and is one of the main ways to discover new meteor
showers! Try it out!
In August, the moon phases are as follows:
Thurs. Aug. 01 last quarter
Thurs. Aug. 08 new moon
Thurs. Aug. 15 first quarter
Thurs. Aug. 22 full moon
Sat. Aug. 31 last quarter
There aren't many bright planets in the August sky, but several are visible:
Jupiter -1.8 in Cancer, low in the east in the morning
Saturn 0.1 in Taurus, low in the east in the morning
If you have any questions on the August showers, or questions on how to
observe them, drop a note to our NAMN Coordinator at meteors@comcastdot net.
Summer is prime observing season, with the Perseids, all the Aquarids, and
some nice fireball producing showers such as the Capricornids and Cygnids.
Get out and enjoy the summer night skies while they last!
4. Upcoming Meetings...
September 3-6, Washington, DC, USA...
The Workshop on Scientific Requirements for Mitigation of Hazardous Comets
and Asteroids, sponsored by NASA, will be held in Washington, DC. The
workshop will review current knowledge of the physics and chemistry of the
interiors of small cometary nuclei and asteroids, and will work towards
several goals: determination of requirements for collision avoidance and
impact mitigation technologies, determination of mission models and
instrumentation needed, and construction of a roadmap for achieving the
knowledge on which to base future systems to deal with possible impacts.
A list of the confirmed invited speakers can be found at
http://www.noaodot edu/meetings/mitigation/invited.html. For information,
contact Nalin Samarasinha at nalin@noaodot edu and check out the conference
website at http://www.noaodot edu/meetings/mitigation.
September 26-29, 2002, Frombork, Poland...
IMC 2002, the International Meteor Conference, will be held in Frombork,
Poland. This is the annual conference of the International Meteor
Organization and welcomes all meteor observers, both amateur and
professional. For information, check out http://www.imodot net and
http://www.astrouwdot edu.pl/~olech/pkim/imc2002/imc.html. For specific
questions, contact Mariusz Wisniewski at pkim@astrouwdot edu.pl
For more information on upcoming astronomy meetings, see: "International
Astronomy Meetings List" http://cadcwww.hia.nrcdot ca/meetings
5. For more info...
NAMN email: namn@atmob.org
NAMN website: http://www.namnmeteors.org
Mark Davis, meteors@comcastdot net
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network
Cathy Hall, chall@cyberusdot ca
Metcalfe, Ontario, Canada
Co-author, NAMN Notes
Lew Gramer, dedalus@alum.mitdot edu
Medford, Massachusetts, USA
Coordinator, Public Outreach
Owner/Moderator, 'MeteorObs'
Kevin Kilkenny, Mail4Meteors@aol.com
Staten Island, New York, USA
Coordinator, Fireballs and Meteorites
Back issues of NAMN Notes can be found on-line 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 or to find out information on our
weekly chat sessions:
Contact Lew Gramer at: dedalus@alum.mitdot edu
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Here's to 'Clear Skies' for August...
August 2002 NAMN Notes co-written
by Mark Davis and Cathy Hall
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