[meteorite-list] Observer's Kit for Nov. 19 Leonid Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:45 2004
Message-ID: <200311071655.IAA17248_at_zagami.jpl.nasa.gov>

http://space.com/spacewatch/leonids_2003_tips_031107.html

Observer's Kit for Nov. 19 Leonid Meteor Shower
By Joe Rao
space.com
07 November 2003

The 2003 rendition of the annual Leonid meteor shower will be much more
challenging to observe than in recent years. For most skywatchers, spotting
shooting stars on Nov. 19 will demand good timing, proper site selection and
some patience.

Below are several observing tips. First, an overview of what to expect.

Meteor showers may conjure an impression of a sky filled with shooting stars
pouring down through the sky like rain. Such meteor storms have indeed
occurred with the Leonids, such as in 1833 and 1966 when tens of thousands
per hour were observed. In 1999, 2001 and 2002, less active but still
spectacular Leonid displays occurred, with a few thousand meteors per hour
being counted by many observers.

The 2003 version of the Leonids are likely to be far weaker than that, but
still worth a look in part because some of the shooting stars promise to be
bright, and the Leonids are known for producing a few stunning fireballs.

Three displays

There are actually three Leonid displays expected this year. The first is
due Nov. 13, when Earth encounters a trail of dust shed by the Comet
Tempel-Tuttle in the year 1499. This Leonid display favors those living in
central and eastern Asia and Australia.

Another burst of activity may come Nov. 19, when Earth interacts with a dust
trail from the year 1533. A rate of up to 100 per hour is possible. Much of
eastern and central North America will be in a favorable position to see
this display, but many of the meteors are expected to be faint.

The best hope for significant Leonid activity may come from a component of
the Leonid stream known as "the Filament," also due Nov. 19.

The Filament is composed of the sum of numerous dust trails shed by
Tempel-Tuttle over many centuries. It should take about a day for the Earth
to fully pass through it. The greatest activity may come near 12:30 a.m. ET
(5:30 GMT) on Nov. 19, highly favoring western Africa and western Europe,
though the northeast U.S. and eastern Canada would also be rotating into
position to see peak activity as well.

While hourly rates may only reach 50 from the Filament, many of these
meteors could be bright and in more than a few cases perhaps even produce
dazzling fireballs. [Details and Timing of Each Burst]

How and when to observe

Watching a meteor shower consists of lying back, looking up at the sky, and
waiting. If they reach their full potential on the morning of Nov. 19, the
Leonids will produce about one meteor sighting every minute or two for a
single observer under a dark country sky.

Any light pollution or obstructions like tall trees or buildings will reduce
the count considerably, so it is wise to select a viewing location in
advance. Even a bright street light or porch light can affect the number of
faint meteors you might see.

The hours after midnight are generally best for watching for other shooting
stars, too, because before midnight we are riding on the back side of the
Earth in its orbit around the Sun, whereas after midnight we are on the
front or advancing side. It's a bit like all the bugs smashing into a car's
front bumper versus the few that can be spotted out the back window.

After midnight the only meteoroids escaping collision are those ahead of the
Earth and moving in the same direction with velocities exceeding 18½ miles
per second. All others we will either overtake or meet head-on. But before
midnight, when we are on the back side, the only meteoroids we encounter are
those with velocities high enough to overtake the Earth.

Therefore, on the average, morning meteors appear brighter and faster than
those we see in the evening. [More Observing Tips]

Speed, Power and Oddities

And because the Leonids are moving along in their orbit around the Sun in a
direction opposite to that of Earth, they slam into our atmosphere nearly
head-on, resulting in the fastest meteor velocities possible: 45 miles per
second (72 kilometers per second).

Such speeds tend to produce bright meteors, which leave long-lasting streaks
or trains in their wake. [The Power of a Shooting Star]

Also, as Leo is beginning to climb the eastern sky near and before midnight,
there is a fair chance of perhaps catching sight of some Earth-grazing
meteors. Earthgrazers are long, bright shooting stars that streak overhead
from near to even just below the horizon.

Earthgrazers are so distinctive because they follow a path nearly parallel
to our atmosphere. The late-night hours of Nov. 18 will hold the most
promise of seeing an earthgrazer as the Earth approaches both the Filament
and the dust trail from the year 1533.

Most Leonids are caused by bits of stuff no larger than a sand grain. A few
larger objects, perhaps as big as a pea or marble, sometimes create dramatic
fireballs. These are so bright they can cast shadows, and their colorful
trails often linger for several seconds. [More about Earthgrazers and
Fireballs]

Count those meteors

Making a meteor count can enhance your enjoyment of a shower. And it is
relatively simple. Just lie down on a long lounge chair or snuggle up in a
warm sleeping bag. Using a pencil and watch, note on a clipboard whenever
you see a meteor. Keep your eyes moving around and don't stare too long at
any one place.

Not all shooting stars will necessarily be Leonids. Other bits of space
debris can race across the sky at any angle. Leonids can race out in any
direction, but they are identifiably by tracing them back to a point of
origin.

A Leonid is one whose path, if traced backward, intersects a point called
the shower's radiant. That spot is inside the curve of stars that marks the
"blade" of the Sickle of Leo.

The Sickle begins rising out of the east-northeast sky after about 11 p.m.
local standard time and is poised high in the south as dawn begins to break.
That is why Leonid watching is generally best between midnight and dawn.

Write an "L" every time you see a Leonid.

Other "sporadic" meteors traveling in random directions may be seen about
once every 5 or 10 minutes. These can be noted on your clipboard with the
letter "S."

Semi-pro counting tips

Meteor counts by amateur astronomers are the primary means used for keeping
track of shooting star history.

To be meaningful to groups that specialize in meteor observing (such as the
American Meteor Society, the International Meteor Organization, or the North
American Meteor Network), your meteor count should conform to standard
observing methods, which include:

  1. Noting your sky transparency (the limiting magnitude of the faintest
     star visible to the naked eye to at least the nearest half-magnitude).
     Do so again if there is any change, such as if the sky becomes hazier
     or, conversely clearer and darker.
  2. Mark the times in your notes for each hour or half-hour, as well as the
     starting and ending times and any periods when you might have stepped
     indoors to warm up or were simply looking away. Do not lump all the
     Leonids you have seen from a long session into one undifferentiated
     total. For example, don't say: "I observed 80 Leonids during a two hour
     and 20 minute time frame."
  3. If two or more people are observing together, each should keep an
     independent count as if he or she were alone. As difficult as it may
     seem, try not to be unduly influenced by somebody who catches sight of
     a brilliant meteor in his or her section of the sky and screams: "Holy
     Mackerel! Did you see that fireball?"

More information about counting meteors and submitting your results is
available from the web sites of the organizations listed above.

The 2003 Leonids will not match up to the performances of recent years. Yet
compared to the two best annual displays (the December Geminids and August
Perseids), this year's Leonids could be categorized as "very good." In fact,
with bright moonlight hampering both the Geminids and Perseids this year,
the Leonids could turn out to be this year's best overall meteor shower.
Received on Fri 07 Nov 2003 11:55:15 AM PST