[Prev][Next][Index][Thread]
(meteorobs) NAMN Notes: July 1999
*****************************
NAMN Notes: July 1999
*****************************
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. The Major Shower for July...
2. The Ecliptic Activity...
3. Other July Showers...
4. Analyzing Plotting Maps...
5. Upcoming Meetings...
6. For more info...
1. The Major Shower for July...
The major shower for the month of July is the Southern delta Aquarids (SDA),
with a maximum on July 28th, at which time the radiant will be at 339
degrees (RA 22h 36m, Dec -16) and forms a triangle with delta and tau
Aquarius. Activity can be seen as early as July 12th, and stretches until
about August 19th. The ZHR, Zenithal Hourly Rate, at maximum is about 20
meteors per hour. These are medium velocity meteors, at about 41 km per
second.
Unfortunately, the peak is right at full moon during July. This will wash
out the sky for many fainter meteors, regardless of how dark your sky is to
start with. However, the Southern delta Aquarids are not the only item of
interest on July 28th. For those of you observing that night, there is an
occultation of the planet Neptune by the moon, visible in parts of North
America excluding the northwest, and in Hawaii. There is also a partial
eclipse of the moon the same night, visible only at moonset for North
American observers, but completely visible for some of our observing buddies
down under, and in Hawaii.
If you are clouded out on the 28th, go for the 29th. If that's the case,
meteor observers will get an added bonus of an occultation of Uranus by the
moon. This is visible in the southern U.S., eastern Canada, and Hawaii.
So, in spite of the full moon, get out and observe!
2. The Ecliptic Activity...
The ecliptic meteor activity continues to be the Sagittarids (SAG), which
stretch from about April 15th to July 15th, and just keep moving from
constellation to constellation along the ecliptic. The Zenithal Hourly Rate
(ZHR) is only about 5 meteors per hour, although this sometimes can be a bit
higher. These are medium velocity meteors, travelling at about 30 km per
second.
The "ecliptic activity" is old comet debris long since spread out along
the path of the ecliptic. It is so spread out and diffuse that we cannot
even figure out what comets (or other bodies) fragmented over time and
formed this band of particles which the earth encounters.
The positions of the Sagittarid radiant are as follows for this month:
July 5: 289 deg, ie. RA 19h 16m, Dec -22, near pi Sagittarius
July 10: 293 deg, ie. RA 19h 32m, Dec -22
July 15: 298 deg, ie. RA 19h 52m, Dec -21
It is very useful to plot the meteors from this ecliptic activity, in order
to try to isolate some of the localized activity, concentrations of debris
as it were, that the earth may encounter.
For assistance in judging magnitudes of any brighter meteors seen (and this
ecliptic activity can produce fireballs), the following are the magnitudes
of some of the brighter planets visible this month, taken from the Handbook
of the Royal Astronomical Society of Canada:
Start of month/11th/21st/end of month:
Venus in the evening sky: about -4.5 all month
Mars all night: -0.4, -0.3, -0.1, 0.0
Jupiter in the morning sky: -2.3, -2.3, -2.4, -2.5
Saturn in the morning sky: about 0.0 all month
3. Other July Showers...
The Pegasids (JPE) reach a maximum on July 10th, with a radiant at 340
degrees (RA 22h 40m, Dec +15), forming a triangle with alpha and zeta
Pegasus, the stars known as Markab and Homam. They have a ZHR rate of about
3 meteors per hour. These are fast meteors, with a velocity of about 70 km
per second, and are believed to be debris from Comet Bradfield (C/1979 Y1).
They are visible from about July 7th to 13th, new moon.
The July Phoenicids (PHE), although not well placed for northern observers,
reach a maximum on July 13th, with a radiant at 032 degrees (RA 02h 08m,
Dec -48), on the Phoenix-Eridanus border and about 30 degrees south of the
front foot of Cetus. The meteor rate can be variable, but is usually less
than a ZHR of 4 meteors per hour. These are medium velocity meteors, at
about 47 km per second. They also are only visible for about 6 days, from
about the 10th to 16th.
The Piscis Austrinids (PAU) reach a maximum the same time as the Southern
delta Aquarids, on July 28th, with a radiant at 341 degrees (RA 22h 44m,
Dec -30) which is about 3 degrees to the right of Fomalhaut. The ZHR rate is
about 5 meteors per hour. These are average velocity meteors, at about 35 km
per second. They are visible from about mid-July through to August 10th.
This shower was discovered by Herschel on July 28, 1865.
The alpha Capricornids (CAP) are a very distinctive shower with nice slow
meteors and bright fireballs. They peak on July 30th, but can be seen all
month and into mid-August. They parade across the sky with a velocity of 23
km per second. At maximum, the radiant is at 307 degrees (RA 20h 28m,
Dec -10) or about 3 degrees up to the left of alpha Capricornus, and have a
ZHR rate of about 4 meteors per hour. This shower is believed to have a
parent body of either the asteroid (2101) Adonis or the comet
45P/Honda-Mrkos-Pajdusakova.
There are also several showers which reach a peak in August, but which start
to become active in mid to late July. For summer observers, there are quite
a few radiants active in the sky. For the positions of these meteor radiants
on any given night, check out the IMO website at www.imodot net, under their
meteor calendar. It gives positions of all showers all year long, at 5 day
intervals. Experienced observers wishing to try their hands at these showers
should also see the article on reducing plots in this newsletter, as it
gives more information on that subject.
The Northern delta Aquarids (NDA) start to become active in mid-July,
although they don't reach a maximum until August 9th. On July 15th, just
past new moon, the radiant is at 316 degrees (RA 21h 04m, Dec -10) about 4
degrees to the left of epsilon Aquarius. These are average velocity, at 42
km per second.
The Perseids (PER), probably the best-known shower to many people, start to
become active about July 17th, although the maximum activity is not until
August 12th. On July 15 (from the IMO table), the radiant is at 012 degrees
(RA 00h 48m, Dec +51), very close to the star nu Cassiopeia about 10 degrees
due north of the naked eye galaxy M31 in Andromeda. These are fast meteors,
at about 59 km per second, and are debris from comet 109P/Swift-Tuttle.
Lastly, the Southern iota Aquarids (SIA) start to become active about
July 25th, just before full moon although the maximum is not until
August 4th. The radiant on July 25th will be at 322 degrees (RA 21h 28m,
Dec -17) which is very close to the star iota Capricornus. These are medium
velocity meteors, at 34 km per second.
4. Analyzing Plotting Maps...
What is involved in analyzing your plotting maps after a night of observing?
You may be like many observers, who really enjoy plotting meteors while out
observing, but cringe at doing the paperwork afterwards! The following is a
basic overview of how to analyze your plots, and is intended for beginners
only. For a more in-depth description of plot analysis, see the IMO Handbook
for Visual Meteor Observers (copies available through the IMO North American
representative).
a) Find out the Visible Showers.
First, you need to know what meteor showers are visible. How else could you
tell if your plotted meteors came from a known radiant in the sky? There are
several ways to find out meteor radiants for a particular night of the year.
One of these is to go to the website of the IMO, the International Meteor
Organization, at www.imodot net and print off their Table 3, "Radiant positions
during the year in alpha and delta." This is under their meteor shower
calendar for 1999. Actually, the whole section is handy, so we recommend
that you just print it all. It's 23 pages long, but is great for reference a
ll year long!
Table 3 gives the position of every meteor shower radiant for the whole
year, at 5 day intervals - for those showers on the IMO "working list." Ok,
so let's assume you are out at new moon in July, Tuesday the 13th. Reading
across the July 15th line, you see that the showers are as follows: SAG,
PHE, CAP, SDA, NDA, PER, and PAU. These stand for (from IMO's Table 2) the
Sagittarids, July Phoenicids, alpha Capricornids, Southern delta Aquarids,
Northern delta Aquarids, Perseids, and Piscis Austrinids. Noticing that the
July Phoenicids are at about -48 degrees in Declination in the sky, you'll
probably disregard these if you are observing from a northerly latitude.
Ok, then take each shower position and adjust it from July 15th to the 13th,
which is your observing night in this case. The SAG radiant on July 10 is at
293 degrees -22, and on July 15 at 298 degrees -21. So, for July 13, you
would take (298-293) divided by 5 days times 3 days, getting 3, then add
that to the 293 for July 10th to get 296 degrees for July 13th. To convert
this to RA, Right Ascension, so that you can read the position off your star
atlas, divide 296 by 15 to get 19.73. That means 19 hours, and .73 times 60
equals about 44 minutes. So, the RA on your star atlas for the radiant
position of the Sagittarids will be 19 hours 44 minutes.
Then go for the declination. You just have to adjust it for the days in
between the 5 day intervals. July 10 says -22. July 15 says -21. So, for
July 13, take (22-21) divided by 5 days times 3 days, to get .6 degrees.
Watch the negative or positive sign here. To get July 13 in this case,
take -22 plus +.6, to get a less negative figure, ie. -21.4 degrees.
So, after a quick (it does get faster with practice) calculation, you now
know that the SAG, Sagittarid radiant, is at RA 19h44m Dec -21.4 degrees on
July 13th.
Using the IMO table, do this same calculation for the other radiants you
observed that night. Note that if you get the IMO publication WGN, they are
listed in there also.
What about other showers not on the IMO "working list?" Well, there will
always be minor showers as well, and maybe new showers found as time goes
on. Where do you find out about them? Some of them are talked about in our
monthly NAMN Notes, which is posted both on the meteorobs email list, and on
the NAMN website at: http://web.infoavedot net/~meteorobs. Some are announced
separately on the meteorobs email list, and special alerts are also given by
the IMO.
b) Mark the radiants on your maps.
Ok, so now you know what's out there! You have calculated the radiant
positions. Now, get out your star atlas, and get ready to plot all these
radiants on your Atlas Brno plotting maps, the ones you used for plotting
the meteors. (These are the maps used by most observers, and are available
through the IMO.)
But - a radiant is not a point. It is an area in the sky. Generalizing, many
meteor showers have a radiant radius of about 5 degrees, making the diameter
of the area 10 degrees. In the IMO Meteor Shower Calendar that you printed
off from the IMO website at www.imodot net, the actual radiant sizes are given
in the individual shower writeups. Most are about 5 degrees in radius. Some
are larger.
To complicate matters, the size of the radiant area increases a bit, the
further the meteor is from the radiant! And - not all the radiant areas are
round. Some are oblong shaped in the sky, longer in one direction than the
other. The sizes of these oblong radiants are included in the individual
shower writeups in the IMO Meteor Shower Calendar, which by now we hope you
have printed off!
Using your star atlas as a guide, figure out about how big a circle of 5
degrees radius is on your Atlas Brno plotting map (ie. 10 degrees across the
whole circle). Then, using a pocket circle template (or freehand), mark the
radiants on the plotting chart. Then mark on the oblong shaped ones. You
might have to mark the same radiant on a couple different maps - but watch,
the scale varies a bit on different maps! Do your best.
c) Analyze your meteors.
Ok, now you are ready to look at the meteors you plotted on your maps. If
you have a lot of meteors scattered between various maps, and many radiants,
this can be a daunting task. It is easy to forget which meteors you have
checked against which radiants. A simple method is as follows:
Get a piece of paper, and list all your meteor plot numbers down the left
hand side of the page. List all the shower codes for your night (SAG, CAP,
SDA, NDA, etc.) across the top of your page, with a column at the end for
SPO, meaning the sporadic meteors which don't belong to a known shower on
the IMO working list of visual meteor showers. Draw lines to make it a grid.
And then, go through each meteor one at a time.
For example, look at your plotted meteor #1. It's on, say, Atlas Brno map
#1. If you are lucky, the radiant it comes from is on the same map.
Your meteor belongs to a particular shower if it:
i. comes from that shower radiant, ie. travels outward from it
ii. is the proper velocity for that shower (some showers have slow meteors
only, some have fast), and
iii. has an appropriate length for its distance from the radiant
What does an appropriate length mean? Well, if a meteor is short, it can
come from close to the radiant, or simply be a meteor from another part of
the sky. However, if the meteor is long, it can't come from really close to
the radiant. Generally, if a meteor is, say, 10 degrees long, it must start
at a distance of no closer than 20 degrees from the radiant. This can be
worded into a rule of thumb: THE DISTANCE BETWEEN THE RADIANT AND THE
STARTING POINT OF A METEOR HAS TO BE AT LEAST TWICE AS LONG AS THE PATH OF
THE METEOR ITSELF. Note that this does not always hold true for the special
case of fireballs.
If the meteor satisfies the 3 criteria listed above, then it belongs to that
shower. Mark an "X" in the box that indicates meteor #1, and the shower
name. Stroke off the other boxes on your grid along the meteor #1 line. You
are done with meteor #1.
If it doesn't come from that shower radiant on map #1, check all the other
radiant areas you have on map #1. Then, if there are any other radiants
marked on the other maps - but not on map #1 - check those particular maps
for your meteor #1. Some shower radiants will be easy to discount - and
stroke off your grid chart. For example, if the meteor is in the bowl of the
Big Dipper, headed to the Pole Star, you know it didn't come from a radiant
in Gemini, or Auriga.
In cases where a meteor is on one map, and might have come from a radiant on
the neighboring map, get 2 rulers, lay one along the meteor path in the
first map, and lay the second ruler (lined up with a couple overlapping
stars) on the second map. Then check the meteor against the radiant areas on
the second map. Hopefully, you don't have to do this too often, or for too
many meteors. Don't forget about the velocity of the meteor while you're
doing this - if a particular shower has fast meteors, and you saw a slow
one, then it's most likely not from that radiant!
If your meteor doesn't match up with any of the radiant areas plotted on
your maps, you should call it a non-shower, or sporadic meteor. Mark an X on
your grid under SPO, and go on to plotted meteor #2. Continue on, each
meteor at a time, marking off the boxes on your grid. The advantage of a
grid is that you don't lose track of which meteors you checked for which
radiants. You eliminate the possibilities one at a time.
d) Time involved.
Is this time consuming? If you have a large number of plotted meteors, and a
lot of radiants you are checking, yes it can be. Make yourself a big pot of
coffee before you start - and if you have any questions, contact one of our
NAMN members to help you out! It is a rewarding task, however - you may just
be the person to help confirm a questionable shower, or to find a new meteor
shower due to your plotting efforts!
5. May's Results...
Meteor activity in May is often considered a slow month because the only
shower approaching major activity is that of the Eta Aquarids. I like to
look at May as the start of the warmer, more active summer meteor season.
When the smoke settled, or fog as the case may be, NAMN observers monitored
meteor activity on 17 separate mornings, logging a total of 320 meteors in
47.78 hours of observing. Kim Hay of Georgia, who was our most active
observer in May, got the month both started off and finished on May 3/4 and
May 24/25 respectively. Way to go Kim!
Unfortunately for us in 1999, the moon was not too kind to the Eta Aquarids,
although there was some activity noted. Norman McLeod of Florida recorded
the first Eta Aquarid of the month on May 5/6 in 1.22 hours of observing. He
followed that up the next morning with 6 in 1.45 hours. His 6 Eta Aquarids
from that morning were the most reported by any observer in any one morning.
Other observers reporting members of this stream include Mark Davis (South
Carolina), George Gliba (West Virginia), Wayne Hally (New Jersey), Pierre
Martin (Ontario) and Kim Youmans (Georgia). A total of only 54 Eta Aquarids
were observed by these observers. For our new members, this clearly shows
the result of moon-brightened skies.
Non-shower, or sporadic meteors, made up the largest segment of meteors
observed during May. Out of 320 meteors recorded this month, 246 were listed
as sporadics! For the most part, sporadic numbers stayed in the single
digits per morning. Mark Davis, George Gliba, Pierre Martin, James Smith
(New Brunswick) and Kim Youmans were the exception to this and recorded
double-digit sporadics at least once during the month.
I would like to thank George Gliba, Wayne Hally, Pierre Martin, Norman
McLeod, Eric Palmer, James Smith and Kim Youmans for submitting reports this
past month. June promises to be even more active so I look forward to
hearing about everyone's results next month.
6. Upcoming Meetings...
July 15-18, 1999:
Starfest, Canada's largest amateur astronomical convention, is being held
near Mount Forest, Ontario. This is a camping event, with observers bringing
tents and telescopes. There are a number of special talks this year on
meteors, meteorites and comets. Dr. Peter Brown will talk on 'Prospects for
a Leonid Meteor Storm in 1999'. Phil Gebhardt will give a talk on 'Radio
Observations of Meteors'. Dr. Richard Herd, Curator of National Collections
at the Geological Survey of Canada will give a presentation 'Meteorites',
and discuss Canadian meteorite research and recovery. Dr.Paul Chodas,
Research Scientist at NASA's Jet Propulsion Laboratory will give several
presentations: 'Calculating Orbits for Asteroids and Comets' and 'Predicting
Comet and Asteroid Impacts'. For more info, and full program details, visit
the website of the NYAA, North York Astronomical Association, at:
http://www.interlog.com/~nyaa
July 26-30, 1999:
The Asteroids, Comets, Meteors 1999 Conference is being held at Cornell
University, near Ithaca, in New York State. Details are available on their
website at: http://scorpio.tn.cornelldot edu/ACM. The abstracts for the talks
and poster sessions are available online and make for some very interesting
reading! Although this is a professional conference, some North American
amateurs will be attending. (NAMN members planning to attend, please also
advise Mark Davis, NAMN Coordinator, at MeteorObs@charlestondot net.)
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, 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.
7. 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
======================================
Here's to 'Clear Skies' for July!...
July 1999 NAMN Notes co-written
by Mark Davis and Cathy Hall
======================================
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html