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(meteorobs) NAMN Notes: August 1999



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NAMN Notes: August 1999
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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://web.infoavedot net/~meteorobs

Contents:

1. Here Come the Perseids...
2. Other August Showers...
3. A Radiant Summary for New Moon...
4. June's Results...
5. Upcoming Meetings...
6. For more info...


1. Here Come the Perseids...

The Perseids (PER), probably the best-known shower to many people, reach a
maximum on August 12th this year, just past new moon on the 11th, so the
conditions for observing them are excellent! The predicted time of maximum
in Universal Time for the primary peak, the strongest, is 23h UT on August
12th. The secondary peak, the normal peak, is at 05h UT on the 13th, and
another peak comes at 13h UT on the 13th. The radiant, the area in the sky
where the meteors seem to come from, is centered on 046 degrees, ie. RA 3h
04m, Dec +58, about a degree north of the star kappa Perseus.

These are fast meteors, at about 59 km per second, and are debris from Comet
109P/Swift-Tuttle. This comet was discovered independently in July 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, and a tail length of
between 25 and 30 degrees. Depending on where it was visible in the sky, and
the moon conditions, this would have been an impressive naked eye object for
country skies.

Perseid meteors have been observed for several thousand years now. This is
one of the oldest meteor showers that we have records for. The earliest
reference to the Perseids seem to have been in the year 36 AD from China.
Because the path of this comet debris, or the orbit, 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. As a result, the Perseids are a reliable meteor shower, seen in
strength each year. This was 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 ZHR, Zenithal Hourly Rate, of the Perseid shower is about 140 meteors
per hour. This means that if you are under a black sky, and the radiant is
right overhead, that you should see, on the average, about 140 meteors every
hour with the unaided eye. These meteors are generally bright, with an
average magnitude of about 2.3 according to Kronk, 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, make them very impressive meteors to witness.
The Perseids will continue to be visible most of the month, until about
August 24th, but will have much lower rates past the date of maximum
activity.

For any of you fortunate enough to be travelling to see the total solar
eclipse on August 11th, don't forget to watch for Perseid meteors! As the
duration of the eclipse is only 2 minutes 22.9 seconds, however, you can
pass on sending in a detailed report. It might, however, provide an
interesting photo opportunity. The closest this will pass to North America
is a spot in the ocean, off the coast of Nova Scotia, Canada, but our
European observing friends will have ringside seats.

The stream of comet debris responsible for the Perseid meteor shower is not
uniform. There is a sorting of particle sizes that has occurred over time.
Hence observers may find that their meteor results will show a different
distribution of magnitudes - average brightness - depending on when they
observe. This will probably not be too evident while observing just on one
night, but if you are out a number of nights, you may notice a difference in
your final numbers on your meteor reports. This is an example of the type
of information that is gleaned from the cumulative reports of observers over
a series of nights.

Results in recent years have found several peaks for the Perseids, with
enhanced activity a number of hours offset from the normal maximum time. In
fact, the 1999 IMO Meteor Shower Calendar lists 3 peaks. So, it is
important to get out around Perseid time as much as possible to observe.
This shower is also known for fireball activity, so it is an exciting shower
for both new observers and seasoned veterans alike.

For any of you interested in trying to capture photographs of meteors, this
is one of the best showers of the year to try for. You may notice, in your
photographs, that there may be several secondary Perseid radiants from which
activity comes, in addition to the main radiant near eta Perseus. Over the
years, meteors have been seen coming from near chi and gamma Perseus, and
minor activity from near alpha and beta Perseus.

What equipment should a beginner use for meteor photos? Use a tripod, a
camera with bulb setting, fast film (ASA 400 or faster), a lens wide open
(or close to it), and exposures of 10-15 minutes each, depending on how
bright your sky background is. Most serious observers use fast black and
white film. However, if you want to use color film and are very near a
light-polluted area, try the high speed tungsten film - this Canadian
observer has found that it will counteract the awful light green sky
background you get near cities. If you have a telescope with a drive
system, try piggybacking your camera on it to keep the stars from trailing.
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 at each end of
the roll, so the processing lab knows where to (and where not to) cut.

If you are new to meteor observing and the Perseids, and want to find out
what data you should record (and get some reporting forms to use), check out
the NAMN website at: http://web.infoavedot net/~meteorobs. The NAMN Observing
Guide (available online or e-mail at no charge) is an excellent resource for
information on how to get involved in observing meteors.

For assistance in judging magnitudes of brighter meteors seen this month,
the
following are the magnitudes of some of the brighter planets visible, taken
from the Handbook of the Royal Astronomical Society of Canada:

Start of month/11th/21st:
Venus: -4.4, -4.2, -4.0
Mars: 0.0, 0.1, 0.2
Jupiter: -2.5, -2.5, -2.6
Saturn: 0.0, -0.1, -0.1


2. Other August Showers...

The Southern iota Aquarids (SIA) reach a maximum on August 4th, with a
radiant at 334 degrees, or RA 22h 16m, Dec -15, about 2 degrees down to the
left of the star iota Aquarius on your star atlas. The ZHR is about 2
meteors per hour. These are medium velocity meteors, at 34 km per second,
and most are faint. They are visible until about mid-August.

The Northern delta Aquarids (NDA) reach a maximum on August 9th, with a
radiant at 335 degrees, or RA 22h 20m, Dec -05, near the star 51 Aquarius.
These are also medium velocity meteors, at 42 km per second, and have a ZHR
rate of about 4 meteors per hour. They are visible until about the 25th.

The kappa Cygnids (KCG) reach a maximum on August 18th. Their radiant at
that time will be at 286 degrees, or RA 19h 04m, 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.
These are slow meteors, with a velocity of 25 km per second. Because of
this, they
are fairly easy to identify. Many have been described as blue-white in
color. Some fireballs have been seen from this radiant, but most of the
meteors are medium bright to faint, according to the IMO Handbook. The ZHR
rate on the 18th is about 3 meteors per hour. These meteors can be seen
from about August 3rd to 25th.

The Northern iota Aquarids (NIA) reach a maximum on August 20th, but can be
seen from about the 11th to the end of the month. At their maximum, the
radiant will be at 327 degrees, or RA 21h 48m, Dec -06, which is about 4
degrees to the left of the star beta Aquarius, Sadalsuud. These are medium
velocity meteors, at about 31 km per second, and like the Southern branch,
most are faint. The ZHR rate is about 3 meteors per hour.

There are also several showers which reached maximum activity in July, but
which can still be seen, at much lesser rates, in the month of August. Among
them are the Piscis Austrinids (PAU) which can be seen until about August
10th, at which time the radiant will be at 352 degrees, or RA 23h 28m,
Dec -26, about 5 degrees due south of the star 99 Aquarius in upper
Sculptor. These are medium velocity meteors, at about 35 km per second. This
shower was
discovered by Herschel on July 28, 1865.

The alpha Capricornids (CAP) are a very distinctive shower, with nice slow
meteors, often producing fireballs. Many of the meteors have been reported
as being yellow in color and they can be seen until mid-August. On August
10th, the radiant will be at 318 degrees, or RA 21h 12m, Dec -6, about 4
degrees to
the right of the star beta Aquarius, Sadalsuud. They parade across the sky
with a velocity of 23 km per second. This shower is believed to have a
parent body of either the asteroid (2101) Adonis or the comet
45P/Honda-Mrkos-Pajdusakova.

The Southern delta Aquarids (SDA) can still be seen until about August 19th.
On August 10th, just before new moon, the radiant will be at 349 degrees,
or RA 23h 16m, Dec -13, about a degree up to the right of the star 94
Aquarius. These are medium velocity meteors at about 41 km per second.

You can see that there are a quite number of Aquarid radiants active in
August. This can be very confusing for new observers. The IMO
(International Meteor Organization) Handbook recommends that: "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'."

Lastly, the alpha Aurigids (AUR) start to become active in late August,
about the 25th, although their maximum is not until September 1st. These
are fast meteors, with a velocity of about 66 km per second. At maximum on
September 1st, the ZHR rate will be about 10 meteors per hour. On August
25th, much lesser rates will be seen from a radiant at 076 degrees, or RA
5h 04m, Dec +42, near eta Auriga, the star known as Hoedus II.

Due to the large number of summer radiants, a suggestion is appropriate for
new observers. If you do not already own a proper star atlas, this is a
good time to get one! One that we recommend is Norton's 2000.0 Star Atlas
and Reference Handbook, edited by Ian Ridpath. It has a good scale on it for
both finding constellations, and plotting meteor radiants. It also contains
a lot of very useful general astronomical articles for new observers - on
everything from telescopes and photography to observing the moon, planets,
deep sky objects, and comets and meteors. Another atlas with very similar
maps, although a bit more cramped as far as scale goes, is Wil Tirion's
Bright Star Atlas 2000.0. Both of these - and others - are available through
Sky Publishing at www.skypub.com or by phoning 1-800-253-0245, and are
described in their free catalog.


3. A Radiant Summary for New Moon...

Because August is such a busy month for meteors, here is a brief summary of
the radiant positions for the days around new moon - when most observers
will be out. It will save you some calculation!

For August 10th (just before new moon):

KCG 284 +58 RA 18h 56m Dec +58
NIA 317 -07 RA 21h 08m Dec -07
CAP 318 -06 RA 21h 12m Dec -06
SDA 349 -13 RA 23h 16m Dec -13
NDA 335 -05 RA 22h 20m Dec -05
SIA 339 -14 RA 22h 36m Dec -14
PER 043 +58 RA 02h 52m Dec +58
PAU 352 -26 RA 23h 28m Dec -26

For August 15th (the weekend after new moon):

KCG 285 +59 RA 19h 00m Dec +59
NIA 322 -07 RA 21h 28m Dec -07
SDA 352 -12 RA 23h 28m Dec -12
NDA 339 -04 RA 22h 36m Dec -04
SIA 345 -13 RA 23h 00m Dec -13
PER 050 +59 RA 03h 20m Dec +59

These are taken from the 1999 IMO Meteor Shower Calendar, and converted into
a format that you can just look up on your star atlas.


4. June's Results...

June provided no surprises to NAMN meteor workers, and was almost a repeat
performance of May if you consider the totals. Fifteen mornings were covered
in June by 8 observers, who recorded a total of 297 meteors in 47.78 hours
of observing.

Similar to the discussion above regarding the Aquarids, the many minor
showers active in June are often a source of confusion to new observers when
attempting to make shower associations. This was recognized, and partially
resolved a couple years ago when the International Meteor Organization
grouped a selection of minor showers into what is called the Sagittarids.
Never reaching more than a handful per hour, the Sagittarids do have a
fairly long activity period, and so are often reported. This month they made
up nearly 50 percent of the meteors reported as a member of some shower.
Still, this is nothing to "hoot" about as it only amounted to 18 meteors!

A shower in need of many more observations is the June Lyrids. You will
often find them listed as being active from June 11 to June 21. This year
NAMN observers again reported seeing some, with Wayne Hally, Scott Moser and
Kevin Kilkenny reporting a few on June 11/12, 13/14, 14/15 and 18/19.
Another shower in need of more observations was monitored this month by
Robert Lunsford. Known as the Xi Draconids, Bob reported 4 on both June
15/16 and 21/22. Of course, the mainstay for observers this month were the
sporadic meteors again. Out of a total of 297 meteors, 262 were reported as
sporadics.

And as always, I would like to thank the following observers for their
reports this month:

Wayne Hally (New Jersey), Kevin Kilkenny (New Jersey), Robert Lunsford
(California), Pierre Martin (Ontario), Scott Moser (Iowa), Eric Palmer
(Nevada), Harry Waldron (Virginia) and Kim Youmans (Georgia).


5. Upcoming Meetings...

August 7-15, 1999:
The 16th annual Mount Kobau Star Party, MKSP '99 will be held in southern
British Columbia, Canada, with talks and events on August 12, 13 & 14. This
is one of Canada's best dark sky sites for observing the Perseid meteor
shower. Speakers include Gary Seronik from Sky & Telescope, Edmonton deep
sky observer Larry Wood, and astronomers from both the Dominion Radio
Astrophysical Observatory in Penticton and the Dominion Astrophysical
Observatory in Victoria. For more information, check out the website at
http://www.bcinternet.com/~mksp or contact the President of the Mount Kobau
Astronomical Society, Jim Failes, at eij@bcinternet.com

September 23-26, 1999:
The 1999 International Meteor Conference (IMC), the annual conference of the
International Meteor Organization, is being held in Frasso Sabino, Italy.
The cost, including conference, lodging, and meals, is approximately $200
U.S. For more information, see the IMO website at http://www.imodot net

January 10-13, 2000:
The 38th annual Aerospace Sciences Meeting & Exhibit of the AIAA, American
Institute of Aeronautics and Astronautics, will be held in Reno, Nevada. A
special session on meteors has been proposed, called 'Aerothermochemistry
effects in meteoric plasmas' and will be chaired by meteor astronomer Dr.
Peter Jenniskens of The SETI Institute at NASA/Ames Research Center, and
co-hosted by plasma physicists Dr. Olga Popova of the Moscow Institute for
Dynamics of Geospheres RAS and Dr. Iain Boyd of the Department of
Aerospace Engineering of the University of Michigan. This is an opportunity
for the plasmadynamics, thermophysics, and fluid dynamics communities to
learn more about the physics, aerochemistry, and optical diagnostics of
meteoroids. Information on the conference can be found on the website at:
http://www.aiaa.org/calendar/asm00cfp.html.


6. For more info...

Contact:
Mark Davis, MeteorObs@charlestondot net
Mt. Pleasant, South Carolina, USA
Coordinator, North American Meteor Network

And check out:
NAMN home page:
http://web.infoavedot net/~meteorobs
Back issues of NAMN Notes can be found on-line at the website.

To subscribe to the meteor email list or
To find out information on our weekly chat sessions:
Contact Lew Gramer at:
owner-meteorobs@jovian.com

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

August 1999 NAMN Notes co-written
by Mark Davis and Cathy Hall
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