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(meteorobs) NAMN Notes: November 1998

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NAMN Notes: November 1998
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Contents:

1. Leonids!!...
2. What if it Storms?...
3. Other November Showers...
4. Upcoming Meetings...
5. From the Archive...
6. For more info...



1. Leonids!!...

Observers could see an exceptional Leonid meteor display this year.

The Leonids (LEO) have a maximum on November 17th, estimated at 19:00 UT,
with a radiant at 153 ie. RA 10h12m, Dec +22, the upper part of the 'sickle'
of Leo. The parent body of this meteor shower is Comet 55P/Tempel-Tuttle,
with a period of about 33.2 years. Sky conditions for the shower are very
favorable this year, being very close to new moon.

Leonid meteors can be seen from about the 14th to the 21st, but the highest
rates will be on the date of the maximum. As the estimated maximum is about
19:00 UT on the 17th, depending where you live, your closest 'dark sky time'
could be either November 16/17 or November 17/18 (see the note about the IMO
maps at the end of section 2). For observers in North America, the rates
are predicted to be slightly better on November 16/17.

Due to the fact that meteor showers are rather unpredictable, it is highly
recommended that, no matter where you live, you observe at least both of
these nights! Scientific models that predict the 'best time' to see meteors
are usually based on studies of what we know about the parent comet's orbit
in relation to the orbit of the earth. However, over the centuries, as
material is shed from the parent comet, each shedding of material takes up
its own orbit. Hence we end up with many slightly differing orbits for the
debris we know as Leonids - and many slightly differing times that we on
earth will encounter that debris.

The Leonids are very fast meteors, with a velocity of about 71 km. per
second. The normal ZHR, zenithal hourly rate, in an average year, is
approximately 40 or more meteors per hour, but is variable.

However, this is not an average year! The dynamics of the debris field in
space are such that the earth may encounter a very large number of
meteoroids this year. Observers are taking this possibility quite seriously.
There are observing teams travelling to Mongolia, China and Australia to
place themselves at a longitude on the earth's surface that has a better
probability of encountering possible meteor 'storm' conditions.
Organizations such as NASA and others with satellites in orbit are quite
concerned about any possible threats to their systems if a meteor storm does
indeed occur.

The last Leonid meteor 'storm' occurred in 1966. Rates recorded in Arizona
reached an estimated 150,000 per hour. This is an often quoted rate, but is
subject to much discussion. There seems to be some agreement, however, that
meteors were coming down at a rate of at least 100,000 per hour! It is
extremely difficult to estimate meteor rates when rates are that high.

This shower is periodic, with storms tending to occur at about 33 year
intervals. It could storm this year...or it could storm next year, 1999.
You may be on the side of the earth that encounters these very high rates...
or you may not. The only way to find out is to go out and observe!


2. What if it Storms?...

What if the Leonids decide to 'storm' this year? To come down at rates of
thousands per hour? Do you know what you would do?

This is not a trivial question. What <would> you do? There are a number of
things you should sit down and think about ahead of time in these next
couple weeks leading up to the shower.

What type of observations would you want to make? Would you want to just
lay back in a lawnchair and enjoy the show? Would you want to make some
visual observations to send in to the meteor organizations? How about
photos with your camera? Would you want to borrow a friend's video camera
and use it to record the storm? Would you want to try looking at the
radiant through binoculars or a telescope to see if the rates seem higher
with the naked eye or with magnification?

What would it be like? Check out the meteor simulation computer program
written by Sirko Molau of the International Meteor Organization. It can be
downloaded from the IMO website at http://www.imodot net. It is listed under
the section 'Software' as 'MetSim'. Have some fun playing with this
simulation, and see how you would manage to observe if the rates really
picked up!

Where will you observe from? If you live in a desert area that is always
clear, you are fortunate. If you live in an area that often has clouds in
November, would you want to travel to see the Leonids to get better viewing
conditions? If yes, where would you go? Think about this now, not the
night before the Leonids, although obviously last minute weather conditions
will play a part in your decision.

How will you observe? Is your observing gear all ready to go? Temperatures
are dropping substantially at night now with winter approaching. Extra
thought must be given to preparing for a cold night out. Batteries in your
tape recorder will die more easily. Batteries in your camera will expire
faster. Take paper recording sheets with you in case all your equipment
ceases to operate! Pack some handwarmers, or if you're near a power source,
consider the electric blanket strategy used by a number of the west coast
observers. Keep your body warm - take hat, gloves, and lots of extra
clothes, even if you don't think you'll need them. Pack one of those heavy
silver survival tarps - they add extra warmth to your sleeping bag, keep the
wind off, and also keep you from getting damp due to heavy dew or frost.

Many experienced observers will be running all kinds of complicated and
advanced equipment to record the Leonids this year. Can a beginner take
some photos of this meteor shower too? Yes!

For basic photos, all you need is a camera, tripod, and cable release. The
camera must have a 'bulb' (B) setting, ie. be able to take a time exposure.
A normal lens, or a wide-angle lens is preferable, and your lens should be
set to either 'wide open' or almost 'wide open', ie. a small f number, and
the focus set at infinity. If you are going to be out under a dark country
sky, use a fast black & white film or a fast color daylight film, ASA 400
or much faster. If, unfortunately, you are stuck close to an urban area
with light-polluted skies, you may wish to try a fast tungsten-based film,
such as Kodak Ektachrome 320T Tungsten, if you want color film. Some
Canadians have found that tungsten film works surprisingly well to
counteract light pollution in color photos. How long should your exposures
be? Take photos for different lengths of time... try some for 5 minutes, 10
minutes, etc. If meteor rates get very high, take shorter exposures. The
most important thing is to record accurate start and stop times for each
picture! That way, your photos can be very useful to the meteor
organizations studying this shower.

If you have a video camera, or can borrow one, use it. You may not be using
the most sophisticated system, but if it ends up that you are one of the
very few people with clear skies for the Leonid maximum, your data can be
very useful! It is also important to have as many observations as possible
from observers widely scattered around the globe in order to learn as much
as we can about this meteor stream. Again, the most important thing is to
record accurate start and stop times for each video clip.

Remember that no matter how simple your observations are, they can be very
useful. Try to plan out your observing, and plan it now - ahead of time.
Whatever type of observations you do, whether they be visual, or
photographic, or video, timing is important. Make sure your watch or clock
is set accurately before you go out, and remember to time your observations.

Lastly, if you decide to just lay back and enjoy the show for part of the
time, do it! A meteor storm is a rare occurrence, and one which we all hope
to experience at least once in our lifetime. For North American observers,
a storm is not expected to occur for this year's Leonids. However, due to
the unpredictability of meteor showers, an unexpected outburst of some kind
is always possible...

More detailed info on how to observe the Leonids can be found on the website
of the IMO, the International Meteor Organization, at http://www.imodot net.
Under the section called 'Hints for Observing the 1998 Leonids', there are
some great maps showing rate predictions depending on where you live, and
excellent suggestions for visual, photographic and video observations.

General information on the Leonids can be found on the Sky & Telescope
website, http://www.skypub.com/meteors/leoking.html


3. Other November Showers...

There are a number of other showers visible in November besides the Leonids.

The Southern Taurids (STA) have a maximum on November 5th, with a radiant at
052 ie. RA 03h28m, Dec +13, about halfway between the horns of Taurus and
the top of the head of Cetus. They can be seen until about November 25th.
These meteors are slow, with a velocity of about 27 km. per second. At
maximum, the ZHR, zenithal hourly rate, is about 5 meteors per hour.
Unfortunately, the moon is very close to full, so the rates will appear
less.

The Northern Taurids (NTA) have a maximum on November 12th, with a radiant
at 058 ie. RA 03h52m, Dec +22, very close to the Pleiades on the Taurus
side. They have a duration similar to the Southern Taurids, and can also be
seen until late November. They are also slow, with a velocity of about 29
km. per second. At maximum on the 12th, the ZHR is about 5 meteors per
hour. The moon situation is more favorable than earlier in the month, being
near last quarter. Both the North and the South Taurids are part of a
complex of meteors related to a number of bodies, one of which is Comet
Encke.

The alpha Monocerotids (AMO) reach a maximum on November 21st, at about
20:00 UT. The radiant is at 117 ie. RA 07h48m, Dec +01, just below Procyon
in Canis Minor. These meteors can be seen from about the 15th to the 25th,
and are quite fast, at about 65 km. per second. The parent body for this
shower may be Comet van Gent-Peltier-Daimaca (1944I). The rates for this
shower have been quite variable in the past, and warrant watching. In an
average year, the ZHR, zenithal hourly rate, is only about 5 meteors per
hour. However, this shower experienced an outburst in 1995, with rates of
over 400 meteors per hour visible for a short period of time. Like the
Leonids, this shower is favored by conditions close to new moon this year.

Lastly, one particular minor shower should be mentioned. It is not on the
1998 IMO working list of visual meteor showers, but in light of all the
Leonid excitement, warrants at least historical mention. The following
information is obtained from Gary Kronk's excellent 'Comets and Meteor
Showers' website at http://medicine.wustldot edu/~kronkg/index.html :

The Andromedids, often referred to as the Bielids, after the parent body,
Comet Biela, reach a weak maximum around November 14 to 17, although
activity may extend to early December. Rates may be about 5 per hour or
less. The radiant is at approximately 26 ie. RA 01h44m, Dec +37, between
the close pair of stars in Triangulum and the handle of Andromeda. The
meteors' atmospheric velocity is quoted as 20 km. per second. In 1872, a
small group of observers in the eastern US recorded about 1000 meteors in
about an hour from this shower, and described them as being slower than
Leonids and generally faint. On the other side of the globe, a group of
observers in Italy saw over 33,000 meteors over about 6 and a half hours.
In 1885, observers in France recorded rates of about 20,000 per hour for a
brief period, with corrected rates estimated perhaps as high as 75,000 per
hour. In this century, rates have been very low. By 1904, rates were down
to about 20 per hour. Due to the breakup of Comet Biela into several parts
back in 1846, and the multiple orbits of meteoroid debris created over the
years, this shower is now essentially quite spread out in duration, with
very low rates. In fact, many observers consider it a shower we will never
see again, due to perturbations in its orbit. However, as with all showers
that have had an outburst history, they still warrant some interest...


4. Upcoming Meetings...

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

The Asteroids, Comets, Meteors 1999 Conference is being held July 26-30,
1999 at Cornell University, near Ithaca, in New York State. Details are
available at their website: http://scorpio.tn.cornelldot edu/ACM/. You can
also leave your name and address, to be contacted with more information. A
number of North American amateurs are planning to attend.


5. From the Archive...

When submitting your reports for archiving, it is extremely important to
provide the correct observer data. Not only will this insure your data is
archived correctly, but it will also make sure you are given proper credit
for making those observations! The standard observer information such as
name, address, date, universal time, longitude and latitude of your site,
and recording method is noted on the top of the NAMN form.

It is standard to use a double date. For example, the observing night of
August 11/12 represents the evening of August 11 and the morning of August
12. Even if the observation began after midnight, the date is still written
as August 11/12. All observations should be recorded in Universal Time if
possible. If you are unsure of how to convert local time to Universal Time,
then it is best to use your local time, and indicate this on the form. With
this information, your local time can be converted to Universal Time.

Your longitude and latitude should be listed in degrees, minutes and if
possible seconds for your observing location. Be sure to include your
elevation above sea level. The data recording method may be by tape recorder
or manual (paper and pencil). More on this later...


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://medicine.wustldot edu/~kronkg/namn.html

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

November 1998 NAMN Notes co-written
by Mark Davis and Cathy Hall
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