(meteorobs) Viewing the Perseids in 2004

[Robert Lunsford]

Every July and August the Earth encounters particles left behind by comet
109P/Swift-Tuttle. These particles appear in our skies above as Perseid
meteors. Hourly rates for these meteors range from one per hour in mid July
to a meteor a minute on the morning of maximum activity, August 12. There
are years when the moon is above the horizon on the morning of August 12.
The moonlight will often obscure the fainter meteors thus reducing the
number seen per hour. In 2004, the moon will be a waning crescent, only four
days before reaching its new phase. Therefore 2004 will be an excellent year
to view the Perseid shower at its best.

While meteor organizations urge observers to monitor the entire Perseid
activity period (July 17-August 24), most people only watch on the night of
maximum activity. This makes sense as most people wish to see the most
activity while losing sleep. If the morning of August 12 is cloudy, very
good activity still occurs on the mornings before and after this date.

Perseid meteors can be seen at any hour of the night. The most activity will
occur just before dawn, when the radiant (the area of the sky the meteors
appear to come from) lies highest above the horizon. During the evening
hours the Perseid radiant lies low in the northern sky (actually below the
horizon for locations south of latitude 32N). The horizon will block a great
majority of the Perseid activity at this time. There will be an occasional
Perseid meteor occur above the horizon. These meteors will skim the upper
portions of the Earth's atmosphere and will last much longer than those that
enter the atmosphere at a more direct angle. From the ground these meteors
will trace out long paths in the sky and will last for several seconds. Many
refer to these meteors as "earth-skimmers". While they are few and far
between, they are often unforgettable sights.

As the night progresses, the radiant rises higher into the northeastern sky.
The horizon blocks less of the activity therefore allowing more meteors to
be seen. After midnight, activity kicks into high gear as the radiant rises
more than half-way up in the sky. By this time Perseid activity can be seen
traveling in all directions, including down toward the north and east
horizons. These meteors would have been blocked by the horizon earlier in
the evening.  Viewers in the Southern Hemisphere are handicapped by the fact
that the radiant will not rise high into their sky (if at all). Therefore
rates seen south of the equator will be very low or non-existent.

How many Perseids will you be able to see? This all depends on your local
conditions. In many parts of the world experiencing typical summer weather,
the skies are hazy. Such conditions would limit the number of Perseids seen
per hour to 20-30 per hour in the hours between midnight and dawn. This
figure does not take into account man-made light pollution. Add this to the
hazy conditions and one would be lucky to see 10-20 Perseids per hour. The
most activity will be seen in rural areas far from artificial lights. Those
who enjoy low humidity will also benefit from the added transparency, which
will allow you to see fainter meteors.

To hold a Perseid watch this year I would suggest the following strategies;
rest during the evening hours and watch during the pre-dawn hours of August
12. Find the darkest safe location possible. Many local astronomy clubs have
secure sites from where you can watch safely. Bring a comfortable lounge
chair and warm blankets. Set up facing half way up in the sky anywhere in
the north to east quadrant. If you have hills or trees in that direction
then face either the east to south or north to west quadrants. Those who
face toward the southwest will see the least amount of Perseid activity.
While it is enjoyable to simply lie back and enjoy the activity, you can
contribute to our knowledge of the Perseids by including hourly counts.
Articles on how to hold useful observing sessions are available at:
http://skyandtelescope.com/observing/objects/meteors/article_98_1.asp and
http://www.namnmeteors.org/guide.html

You might also try to capture Perseid meteors on film. Any camera capable of
time exposures can record meteors. Old time mechanical single lens reflex
cameras are best suited for meteor photography. Exposures should be at least
one minute and probably less than fifteen. This all depends on the condition
of your sky and the sensitivity of your film and lens. An urban sky will
cause film to fog quickly limiting exposures to less than five minutes.  The
best combination is a rural sky with a "fast" lens and film. Be sure aim the
camera in the lower half of the sky, where most of the activity will occur.
More details on meteor photography appear in the articles mentioned above.

While viewing the Perseids you will notice slower meteors coming from other
directions. These are caused by minor showers and random activity. Known
areas that also produce meteor activity this time of year include the
constellations of Aquarius, Cygnus, Taurus and southern Perseus. Suspected
areas of activity also include Lacerta, Pegasus, and Cetus. If recording
activity it is important to note meteors from these sources.

Eastern European and western Asian observers have an added opportunity of
viewing a possible outburst of faint Perseids near 21:00 Universal Time on
August 11. These particles were released during the comet's 1862 trip
through the inner solar system. This outburst will most likely last less
than one hour. No one know the exact strength of this possible outburst, but
it should be impressive when added to the normal 40-60 Perseids one would
expect to see at this time.

Meteor organizations and publications are interested in receiving your
hourly counts. The more information you provide the more valuable your data
will be. They can be submitted to the following email addresses:
Lunsford at amsmeteors.org, visual at imo.net, and meteorobs at meteorobs.org

This article just touches on the main aspects of viewing the Perseids this
year. If anyone has specific questions please post them to the meteorobs
list and I will reply ASAP.

Clear Skies!

Robert Lunsford