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(meteorobs) Radiant Rising, No. 3, July/August 1997

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RADIANT RISING                               Number 3, July/August 1997

New Jersey Astronomical Society           North American Meteor Network
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        THE PERSEIDS ARE COMING! THE PERSEIDS ARE COMING!!
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   Finally, the highlight of 1997's meteor season is at hand. Since all the
other major showers during the remainder of the year must battle the moon,
this is the best opportunity to do some significant observing. Let us start
with the Perseids, then we will backtrack to the busy area surrounding
Aquarius along the ecliptic.

   The Perseids have been observed for two millennia, and are a favorite for all
Northern Hemisphere observers. The pleasant temperatures of summer combine
with a high rate and long period of activity to provide a fine display every
year, even when the peak is hampered by the moon. As an added bonus, since
comet P/Swift-Tuttle passed through the inner solar system in the early
90's, there are two peaks; the traditional broad one, material in the main
stream which has been dispersed throughout the comet's orbit, and an another
peak, about 12 hours
earlier, consisting of fresher material from one of the more recent passages
(suspected to be 1862). When this outburst began in 1991, the ZHR was near 400.
Since then it has declined to a level closer to the traditional peak (100),
but is still quite variable. This year, the early peak is positioned well
for the North American continent, predicted to be 0600 UT, August 12th.
[Note: Information in the June WGN suggests a slightly later time of 0830
UT; in the following discussion these times will be in brackets] This works
out to 2 AM [4:30 AM] on the morning of Tuesday the 12th for the east coast,
and 11 PM Monday night [1:30 AM Tuesday] on the west coast. Moonset occurs
about half an hour after midnight, and with the moon being half lit, it will
hamper observations before then. Nautical twilight is about 5 AM, depending
of course on your latitude and longitude, so there will be at least four
fully dark hours available. The traditional peak is in mid-afternoon of the
12th for us, so we'll have to leave that to our friends in Asia, although
the west coast may see an increase just before dawn. In any case, enjoyable
rates should be visible several days before and after this night. One other
point that should be mentioned is that these times are predictions, and
could be off by several hours. Only we can collect the data that will
determine what actually happened. Last Quarter moon is on the 25th of July,
providing some after midnight hours free of the moon's interference.

   Be sure to accurately determine the radiant's location on the nights when you
observe, since before the new moon of the 3rd, rates will be low enough that one
must use great care in separating the Perseids from sporadic meteors. It
will help if you can learn the Perseid's speeds at different distances from
the radiant. Remember, the closer to a radiant a shower member appears, the
slower it projects on the sky. This is why by placing your field of view 30
to 50 degrees away from the radiant, you can see the meteors moving faster,
which makes them easier to spot, as well as more visually pleasing since the
path is longer. For those who are plotting, it is best not to know the exact
location of the radiant....let the plots speak for themselves! When rates
exceed 20 an hour, it is best to stop plotting and start counting, so have a
secret chart that you can pull out with the exact radiant targeted in case
you need to switch during the night.

   By Friday night, the 8/9, things really begin to perk up. There should be
more Perseids than sporadics, and we're on the home stretch. You should be
able to observe through Friday night (about an hour between moonset and
twilight) on the 15/16. After that the near full moon does not set until
after twilight in the morning, so we can catch up on sleep and digest all
our observations. So the plan is....take vacation the week of the 12th!


Perseids (PER):
Period of Visual Activity:   July 17 to August 24
Peaks:   Early peak 06 [0830] UT Aug 12, Traditional peak 18 UT Aug 12th
ZHR:   Early peak ~ 150, variable; Traditional ~100
Velocity:   59 kps


   Before leaving the northern region of the sky, we should mention the
kappa-Cygnids (KCG). This minor shower's peak is the night before the full moon,
but since you might see one or two meteors from this shower during your Perseid
watch, the radiant positions are listed below. These are much slower than the
Perseids, and the radiant is not too far away, so it should be easy to keep
an eye out for them. Once again, if you are going to try to count these, be
sure to know the exact position of the radiant, since with a rate near one
an hour, it must line up very closely, and be quite slow.


kappa-Cygnids (KCG):
Period of Visual Activity:   Aug 3 to Aug 25
Peak:   August 17
ZHR:   3
Velocity:   25 kps


   The remainder of the meteor stream activity this month is centered along the
ecliptic from Aquarius through Capricorn. The primary visual shower is the
Southern delta-Aquarids (SDA) which reach a maximum on July 28th. As with
all these showers, the SDA radiant doesn't rise very high. Despite a ZHR of
up to 20, their low elevation will allow only a small percentage to be seen
here in North America. The Northern delta-Aquarids (NDA) barely reach visual
levels on August 8th. Both of these shower's meteors have velocities near 41
kps - slower than the Perseids. The Northern and Southern iota-Aquarids
(NIA, SIA), slower still at around 34 kps, require accurate plotting and
experienced determination of speed to verify.

   The alpha-Capricornids (CAP) are very slow (23 kps) meteors, furthest to the
west, and reach detectable visual levels near their peak on July 30th. Finally,
most southerly of all, are the moderately slow (35 kps) Piscis Austrinids (PAU).
Like the SDA's, they also peak on July 28th, but near Formalhaut which is at
such a low elevation that only a few meteors at most can be spotted.


RADIANT LOCATIONS:
Shower     July 25                July 28                July 30
SDA        337d (22h28m), -17     339d (22h35m), -16     340d (22h40m), -16
PAU        338d (22h32m), -31     341d (22h44m), -30     343d (22h52m), -29
CAP        303d (20h12m), -11     306d (20h24m), -10     308d (20h32m), -10
SIA        322d (21h28m), -17     326d (21h42m), -16     328d (21h52m), -16  
NDA        323d (21h32m), -09     325d (21h42m), -08     327d (21h48m), -08

Shower     Aug 5                  Aug 10                 Aug 12
SDA        345d (23h00m), -14     349d (23h16m), -13     350d (23h21m), -13
PAU        348d (23h12m), -27     352d (23h28m), -26     354d (23h34m), -26
CAP        313d (20h52m), -08     318d (21h12m), -06     320d (21h20m), -05
SIA        334d (22h16m), -15     339d (22h36m), -14     341d (22h46m), -14
NDA        332d (22h08m), -06     335d (22h20m), -05     337d (22h26m), -05
NIA        312d (20h48m), -08     317d (21h08m), -07     319d (21h16m), -07


   Finally, a few comments on what you should look for depending on your
experience level. These are recommendations only. Others may have different
opinions, with perfectly valid reasons. (Note: you should do what the
organization you report to recommends, so that it can be properly recorded
in their database.) 

   First let's address the novice observer. If your first observations will be
during the Perseid peak period (Aug 8-15) you should concentrate on just the
Perseids. Record your meteors as PER or sporadic (Spo). There's enough to
learn and concentrate on: accurately recording the limiting magnitude, and
the meteor
magnitudes, and determining whether a meteor is a Perseid or not is enough to
absorb at one time.

   For the observer who has a night or two under his or her belt, it may be
worthwhile to try and discriminate the Aquarid activity from the sporadics, in
addition to the Perseids. If you know the area that all the Aquarid radiants
cover, you can record them as AQR (Aquarids). Your observations will have
more scientific value without giving you too much to learn at once.
Remember, higher quality data is more important than a lot of low quality
information.

   The next level for a visual observer is appropriate for someone who has seen
enough meteors to know what fast and slow meteors are. You can then hope to
discriminate between the medium fast SDA's and the slow CAP's. The iota-Aquarids
remain in the domain of plotting and video observations.

   Here is a suggested plan for observers during this lunar period. This
does not include the Perseids, which should be a constant subject of
attention throughout. Experienced observers should ignore this!

   Up until the new moon (Aug 3rd), the majority of the activity from this
region is from the Southern delta-Aquarids and the alpha-Capricornids (CAP).
Since the SDA's are faster than the CAP's, if your field of view is
positioned above and between them, in NW Pegasus for example, you should be
able to tell the difference, as well as continue to monitor the Perseids.

   Between the New Moon (Aug 3) and Perseids weekend (Aug 8/9), the N & S
delta-Aquarids reach comparable (if low) levels, the PAU's and CAP's fade
away, and the stage is cleared for the Perseids. For those who are plotting,
you should consider plotting only non-Perseids as rates increase. 

   Once the Perseids are in full swing, more useful information is provided by
accurate counting. For the peak night, the IMO is recommending that the count be
broken into 15 minute intervals. At this time all the showers in Aquarius have
rates below 3 an hour, so again, recording them as Aquarids (AQR) might be
the best thing to do, instead of spending much effort separating the
individual radiants. These are: PAU, SDA, CAP, SIA, NDA. Keep an eye out for
the KCG's since they are high in the sky near the Perseids.

Above all, have fun!


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NAMN NEWS and NOTES
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A couple more member profiles:


Name: Thomas Wojack.
Bobbies/interests: Around 1987, me and my family (I was 5 years old then) would
look at the moon with just naked eye. In 1991 I found a 60mm refractor and just
looked at the sky. I saw several fireballs! Unfortunately, I lost the
eyepiece. So, I saved $25 and bought another eyepiece. But this eyepiece had
too much power and disliked telescopes. We were awed with the piece of rock.
In 1992, I started getting serious with astronomy. I subscribed to ASTRONOMY
Magazine. I was baffled by the amount of stars visible in binoculars. In
1995, I decided to give telescopes another try. Bought a 6" telescope from
Orion. It was incredible. I watched Jupiter's moons dance and saw the moon
(IMPRESSIVE!). I observed the horsehead nebula (beautiful and super easy to
find!). In 1996, I joined ALPO to observe the moon. I also got hooked on to
the Internet, which has overwhelming astronomical resources. I can get
images for basically free. I have never enjoyed astronomy so much! When I've
been playing outside, I would see some sporadics. BTW, in 1993, I observed
the leonids, and I saw 10 in about 25 minutes. Meteors were the most amazing
thing I had ever seen. 


Name: Thom Morgan
Hobbies/interests: anything to do with astronomy, Bonsai, foreign languages
(Deutch, Espanol, Nihongo, Tagalog, and Cebauno dialects in Phillippines)
and the Raleigh, North Carolina dart league. I have a bachelor of science
degree in
landscape architecture from Michigan State, where I loaded my course work
with the physical sciences. Soon to be married when my fiance arrives here from
Phillippines.

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Copyright 1997 New Jersey Astronomical Society & North American Meteor Network