Leonid Observer’s Guide
by Dave Snyder
Revised: October, 2002
In November 2002, the Leonid meteor shower will return and may possibly be
a spectacular event. In previous years Leonids have produced large numbers
of meteors, however the number that will be seen is affected by several
factors.
- Particle density - All meteor showers are associated with a parent object
(such as a comet). In some cases the object no longer exists, but the
remnants of the object are still present. In other cases the object
still exists, but there are fragments from the object in the same orbit.
In any event the object has
a definite orbit around the sun and that orbit has a specific period.
The parent object of the Leonids has a period of 33 years and thus the particle
density is highest every 33 years and the meteor shower from the
Leonids is most intense every 33 years.
In the case of the Leonids, the particle density is most
intense over a period of about five hours. So for optimal viewing
you need to be observing during that period.
(Other meteor showers, such as the Perseids, have a more even particle distribution).
Unfortunately, it will be daylight in
some parts of the world at the maximum, at such locations it will not
be possible to see the maximum activity.
It is possible
to predict the peak time, but predictions for the Leonids have been inaccurate
in the past (and different models can give different predictions).
- The radiant - The meteors from the Leonid shower appear to travel from a position within
the constellation Leo, this position is known as the radiant. While it is
possible to see some meteors even if the radiant is below the horizon, more
meteors will be seen if the radiant is well above the horizon. The position
of the radiant will change over the course of the night due to the earth’s
rotation. For observers at 42 degrees north latitude, the radiant rise time is approximately 11 PM (standard time) or
10 PM (daylight savings time).
(The exact time varies somewhat dependent on your longitude).
However if your horizon is not perfectly flat, then the rise time will be later.
The radiant is not optimally placed until a few
hours later.
- Local time - Everything else being equal, the number of meteors increases
as the evening progresses (you will tend to see more meteors after midnight than
you will before midnight). The maximum time is 6 AM local time and
the minimum is 6 PM local time. If it is perfectly clear and dark, and if the number
of particles is constant over a long period, you should be able
to observe roughly three times as many meteors at 6 AM as you can at 6 PM.
However as was just explained the number of particles will not be constant
over a long period.
- Sky conditions - One should expect to see about 8 times as many Leonid meteors
from a dark location as one should expect from a typical location
within a city. (This is assuming that the
the ideal site allows viewing objects of magnitude 6.5,
the city location
allows viewing objects of magnitude 3.5 and the only meteors visible are from
the Leonids).
So it will help to pick an observing site well away from bright city lights.
Starting your observing session well before the maximum intensity will
also help as this allows your eyes to become adapted to the darkness.
Obviously if it is cloudy, this may reduce the number of the number of
meteors you will see.
On any given night you
should expect to see 5 to 10 meteors per hour (under ideal sky conditions), however
a good fraction of those meteors are very dim (they look like tiny flickers of
light). Even if your view of the Leonids is not ideal, you may still find
an increase in the number of meteors (and if you miss this opportunity, there
will not be another opportunity to view the Leonids for another 33 years).
The best way to observe meteors is by eye without optical aid. You can
observe with binoculars, this increases the number of dim objects you can see,
but it also reduces your field of view. In addition it is also possible
to observe meteors with an ordinary FM radio (this can be done during daylight,
at night, if it is cloudy or if it is clear).
Update (December 1999)
When reporting observations of a meteor shower, people talk of ZHR
which is the number of meteors an experienced observer should expect under
good observing conditions.
On November 17/18 at Hudson Mills Metropark (near Dexter Michigan), we had a turn out of
several hundred people. The number of meteors observed was small.
(Later reports suggest the peak particle density occurred at 0200 GMT when the radiant was below the horizon. While we had
a reasonable horizon with only a few trees in the distance, there was
a lot of light pollution in the direction of the radiant which obscured many
of the dim meteors which otherwise might have been observed).
One group present at Hudson Mills Metropark reported a total of about 70
meteors over the course of the evening.
I would not be willing to
translate that into a ZHR under the circumstances.
Most of these meteors were not Leonids (many were Taurids and others were
sporatic). It is clearly less
than one would expect during the peak of the Perseid meteor shower (which
occurs on or around August 11 every year) and cannot be described as a meteor storm.
Observers in the middle east described a ZHR of approximately 5000.
There were numerous reports of a group of objects passing across the
sky on the evening of November 16th (about 7 PM Eastern Time). There were observations all across the
Midwest United States. Press reports suggested this
was connected with the Leonid meteor shower, however this is not likely.
These objects were almost certainly space debris that burned up in the earth’s
atmosphere.
Update (November 2000)
In the year 2000, we were clouded out at Hudson Mills.
Update (November 2001)
In 2001, it was clear at sunset, but heavy fog settled in, preventing observations
from most of Michigan. However a few Michigan locations were not fogged
out; many North American observers saw over 1000 meteors per hour. See
2001 - A Leonid Odyssey (November
20, 2001).
Photographs from the 2001 event are available
(these are photographs of people, not meteors).
Update (November 2002)
It was completely overcast in 2002 in Southeast Michigan, and no meteors were
observed.
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