(meteorobs) NAMN Notes: August 2008

[meteors at comcast.net]

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NAMN Notes: August 2008
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NAMN Notes is a monthly newsletter produced by the North American Meteor
Network and is available both via email and on the NAMN website at:

http://www.namnmeteors.org


Contents:

1. The Perseids - The Public’s Shower...
2. July’s Southern Showers Wind Down...
3. KCG, the “Other” August Shower...
4. Other Showers of Interest...
5. New Showers from Video Data...
6. Magnitude References...
7. For More Information...


1. The Perseids - The Public’s Shower...

If you walk up to the man or woman on the street and ask them about
meteors and if they’ve seen any, about half will look at you dumbfounded
with no idea what you are talking about. Most of the rest will mention
something about “those meteors in the summer”. The Perseids are the most
accessible shower to the general public and the casual meteor watcher.
The weather in the northern hemisphere is warm, though the skies are
often hazy. Fortunately, the Perseids are generally bright and swift, so
can punch through the less than ideal skies. This has likely been going
on for nearly two millennia, since the earliest records of this shower
go back to 36 AD.

The parent, 109P/Swift-Tuttle, was the third comet discovered in 1862,
and in fact as a result of that discovery, Giovanni Schiaparelli made
the first association between comets and meteor showers. At that time,
calculations of the comet’s orbit (with a lot of uncertainty) indicated
a period of about 120 years, meaning the next return was expected in
1980. When it failed to appear on schedule, other possible orbits were
considered leading to the correct period of ~ 133 years. For a good feel
of the history of the comet I suggest reading Gary Kronk’s excellent
page on the subject at:

http://cometography.com/109p.html

Earlier returns have been found (using the correct orbital period) going
back as far as 6 BC. The comet has been around for thousands of years,
and its orbit is stable enough that it will be around thousands of years
into the future.

The orbit is highly inclined (113 degrees), eccentric, and retrograde,
orbiting the sun in the opposite direction from 98% of the material in
the solar system. The aphelion is well outside of that of Neptune’s
orbit, at 51 AU. That’s about as far out as Pluto gets, near the outer
edge of the Kuiper Belt. The perihelion (closest approach to the sun) is
just inside of Earth’s orbit. These factors combine to make the Perseids
a northern shower with swift meteors of about 59 km/sec when they hit
the atmosphere. It is the largest periodic comet nucleus to visit the
inner solar system.

The Perseids no longer produce the exceptional rates that occurred near
the 1992 perihelion, but still are reliable and bright, and so put on a
good show when skies permit. The rate rises slowly from mid July until
the peak period, then falls more rapidly afterward, ending by August
26th. As for the peak itself, I have examined last year’s IMO on-the-fly
data (no full analysis has been completed) and it shows that high
activity occurred for more than 2 full days. One way to measure a peak
is what is called Full Width Half Maximum (FWHM), the period when the
rate exceeds half the peak value. Last year that occurred from Solar
Longitude 139.3 to 141.5. This year that would be from 20 UT August 11th
through 02 UT on the 14th.

The IMO lists the peak at Solar Longitude (SL) 140.0 to 140.1 or 12-14
UT on the 12th. If one examines last year’s results though, at:

http://www.imo.net/live/perseids2007/

that particular time appears to be in a lull between peaks earlier and
later. There is evidence of a narrow peak about SL 139.5, a plateau of
high activity from 139.7 to 139.9, and later peaks at 140.5 and 141.4.
The peak at 140.5 could be a return of one of the extra ones that were
last seen in 1999 from recent debris. The point here is that you should
not focus on the narrow 2 hour window of the predicted peak, but rather
observe well before and after. That’s good news for North America, since
the predicted time is not very favorable, occurring during the day of
the 12th.

One possible explanation for this is the filaments of old trails ejected
hundreds to thousands of years ago. Peter Jenniskens and Jeremie
Vaubillion calculated 3 filaments would arrive at SL 139.4, 139.45, and
139.81 last year; this was the time when the plateau mentioned above
occurred. The same trails (from 1479 and 513 AD) are also expected to
intersect the earth again this year from 139.6 to 139.83, so if those
calculations are valid, we might expect enhanced activity between 02 and
07 UT on the 12th. That is 10 PM EDT (7PM PDT) on the 11th until 3AM EDT
(midnight PDT) on the 12th. That’s a few hours before the predicted IMO
peak, and almost perfect for North America.

An interesting fact I did not realize, but discovered while preparing
this month’s notes, is that the day after the peak, the radiant actually
moves out of Perseus into the constellation Camelopardalis. Imagine,
after all these years of following meteors, there are always things to
be learned!

During the peak nights the moon will be setting after midnight, so the
darkest skies will be between then and dawn. That’s OK, because due to
the radiant rising higher during the morning hours, the best rates will
occur near dawn anyway. However, even before then, the brightness of the
Perseid meteors and the low elevation of the moon should allow plenty to
be seen. Just be sure, as usual, to accurately estimate the Limiting
Magnitude of your sky if you are submitting scientific data. The NAMN
has a tool to help with that at the following URL:

http://www.namnmeteors.org/lm_calc.html

Here are the radiant locations for selected mornings during August.
Between these dates you can interpolate. Before and during the peak the
radiant lies in Perseus, as you would expect. You can also see a
graphical representation of this by accessing the IMO 2008 meteor shower
calendar:

http://www.imo.net/calendar/2008

PER (Perseids) 59 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 1;  RA 032 (2:07); Dec +55 (New Moon)
Aug 7;  RA 040 (2:41); Dec +56
Aug 13; RA 049 (3:14); Dec +58 (Before the Full Moon of August 16)
Aug 19; RA 056 (3:43); Dec +58 (After Full Moon)
Aug 26; RA 064 (4:16); Dec +59 (End of Activity)

The IMO on-the-fly chart for 2008 can be seen at:

http://www.imo.net/live/perseids2008/

as data is reported to them via the online data entry form.

Good luck, and clear skies to all!


2. July’s Southern Showers Wind Down...

The activity from the Southern delta Aquarids (SDA), alpha Capricornids
(CAP), and Piscis Austrinids (PAU) are just past their peaks as the
month begins, coincident with the New Moon. And of course, the
Antihelion radiant (ANT) continues with low levels throughout the month.
These showers are all best observed close to 1-2 AM daylight time each
morning. The PAU and CAP showers end by the full moon, while the SDA
shower continues until the end of the month. The meteor velocity ranges
from 41 km/sec for the SDA, 35 for the PAU, 30 for the ANT, and 23
km/sec for the CAP meteors. All are easier to see the further south you
are. While some can be glimpsed from 45 degrees north, many more can be
seen further south. Here are positions on selected mornings (see the
2008 IMO calendar mentioned above for a projection of the radiants on
the constellations in the neighborhood).

SDA (Southern delta Aquarids), 41 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 1;  342 (22:47); -15
Aug 7;  347 (23:06); -14
Aug 13; 351 (23:23); -12
Aug 19; 355 (23:41); -11 (End of official IMO activity)
Aug 26; 001 (00:03); -10 (From IMO video data)
Aug 31; 006 (00:26); -07 (From IMO video data, end of activity)

CAP (alpha Capricornids), 23 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 1;  307 (20:26); -09 (New Moon)
Aug 7;  311 (20:46); -08
Aug 13; 316 (21:05); -05 (Before Full Moon)

PAU (Piscis Austrinids), 35 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min);Declination
Aug 1;  345 (22:59); -28
Aug 10; 352 (23:28); -26

ANT (Antihelion), ~ 30 km/sec
(Remember, this radiant is much larger than the other showers, 15 X 30
degrees in size; 30 degrees wide along the ecliptic, and 8 degrees above
and below, centered  on the ecliptic.)
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 1;  321 (21:24); -13
Aug 7;  327 (21:48); -11
Aug 13; 333 (22:12); -09
Aug 19; 339 (22:36); -08
Aug 25; 344 (22:56); -05
Aug 31; 350 (23:20); -03


3. KCG, the “Other” August Shower...

This is one of my personal favorite showers. While the rates are low,
the kappa Cygnids fly in stark contrast to the fast Perseids. They are
much slower (25 km/sec, less than half the speed of the Perseids), and
from what many have seen, tend toward a golden color, often with a
bright terminal burst. Last year’s activity appeared to be somewhat
higher than normal, with many bright bursts near the end of the
individual meteors. While this year the full moon occurs near the “peak”
on August 17th , the peak is not a very sharp one; in fact IMO video
data shows almost flat levels throughout the active period. That matches
my impression, which is there is nearly a constant low level of KCGs
throughout the month. The radiant doesn’t move a great distance, being
so close to the ecliptic pole. Recently, Peter Jenniskens has proposed a
possible remnant of the comet that formed this shower. See the article
on the space.com website:

http://www.space.com/searchforlife/080529-seti-kappa-cygnids.html

He suggests the minor planet (asteroid/comet) 2008 ED69 is a remnant of
the parent comet. Confirmation of that remains in the future. Positions
on selected dates are listed below; you will need to look at the 2007
IMO calendar for the graphical representation since it is not shown this
year due to the coincident full moon:

http://www.imo.net/calendar/2007

The radiant lies between the northern wing of Cygnus and Draco’s head
all month long.

KCG (kappa Cygnids) 25 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 3;  RA 283 (18:50); Dec +58 (Start of Activity)
Aug 8;  RA 284 (18:54); Dec +58
Aug 13; RA 285 (18:58); Dec +59 (Before Full Moon)
Aug 19; RA 286 (19:14); Dec +59 (After Full Moon, KCG “peak” morning of
Aug 18)
Aug 25; RA 289 (19:16), Dec +60 (End of Activity)


4. Other Showers of Interest

Many minor showers appear to populate the August skies. Perhaps the
reason there is so much confusion is that most observers concentrate on
the Perseids, while high sporadic rates at this time of year lead to
spurious radiants. The only way we can help sort this out is to be aware
of other potential showers, and be as accurate as possible in our shower
associations. These are showers for the experienced observer only, since
you must know the radiant position very accurately, and also have the
skill to estimate angular velocity. Let’s first examine showers that
have been reported to the NAMN over the last few years. ALL should be
reported to the IMO as sporadics for the time being, but please use the
designations below in reporting to the NAMN.

Big Trouble in River City...

The first we will examine is the activity in Eridanus (“The River”)
during August. Therein lays much confusion. These showers are not on the
current IMO working list, but they used to be. The first, the
pi-Eridanids (ERI), active from Aug 20 to Sept 5 had daily radiant drift
of +0.7 in RA, and +0.2 in Dec, with a meteor velocity of 59 km/sec. The
other, the epsilon-Eridanids (EER) was supposed to be active from
September 9-12, but no radiant drift or velocity was noted. In fact, the
position at the EER peak day is almost identical to the ERI shower, so
there’s not much logic to giving them different names. The IAU list
includes an ERI shower, the eta Eridanids active from Aug 3-14 with 64
km/sec meteors (and no radiant drift). Meanwhile they call the IMO ERIs
the epsilon-Eridanids (EER), with a meteor velocity of 59 km/sec and
radiant drift of +0.7 and +0.2, per day. Hmmmmm. They are shown as
equivalent to the pi Eridanids, and are active from Aug 20 to Sept 16th.
Just to add to the fun, Gary Kronk found another shower from 10 or 15
degrees higher in Declination. Whew, mighty confusing!

After projecting the radiant positions in time, it appears we have 2
showers. Since the IMO database in the past has used ERI for the common
one, we will adopt that code for the shower active from Aug 20 to Sept
16, the positions are listed below. For the other shower, which the IAU
calls ERI, and does not show in the old IMO list at all, we shall use an
IER code, to differentiate it from the other longer period shower. It’s
only active for a few days from a much different location. In this way
we can preserve the separate identities. Hopefully in the future, this
will be cleared up, and our data recorded this way can help. Neither of
these showers showed up in the IMO video data, so these are very minor
showers at best.

ERI (pi/epsilon Eridanids) 59 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min);Declination
Aug 20; RA 043 (2:52); Dec -18
Aug 28; RA 049 (3:15); Dec -16 (Peak)

IER (IAU ERI) 64 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
August 3-13; RA 045 (3:00), Dec -13;  “Peak” August 10

Horsing Around...

The next shower is the Upsilon Pegasids (UPG). The existence of this
shower has been hotly debated since its discovery in 1975. Does it
exist? Doesn’t it? So far the answer is inconclusive. Last year, there
appeared to be some activity, but great care must be taken to ensure
that any meteors are truly associated with this radiant, and not chance
sporadic meteors. These are supposed to be “swift”, but no velocity has
been measured. The radiant, if it exists, is in the Great Square of Pegasus.

UPG (upsilon- Pegasids) “swift” km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
July 25-Aug 19; RA 350 (23:40); Dec +19

A different (Tri)Angle...

In 2007, a number of meteors were reported to the NAMN in August from
the IAU shower TRI (August Triangulids), which is known to exist from
radar data. I have listed positions below for the TRI shower, these
should be used for meteors from this area in August. These would be fast
meteors (59 km/sec), and most likely faint, since they do not appear to
show up in video reports. The radiant below is a weighted average of the
radar data positions. The ATR radiant will be listed next month.

TRI (August Triangulids)  59 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 6-14; RA 136 (9:04); Dec +33


5. New Showers from Video Data...

The next batch (again, only for the experienced observer) are showers
detected in the IMO video analysis. These all have very low rates, with
unusual characteristics. The odd thing is that all these showers appear
to move rapidly to the west and south during their activity periods,
unlike almost all others which move about a degree to the east every day
as the earth orbits the sun. So far, no satisfactory mechanism has been
proposed to explain this. Yet here they are, so let’s take a look.

The first is the August Capricornids (AUC). These are noticeably slow
meteors from near alpha Capricorn. The CAP shower is gone and well to
the east at this time, as is the antihelion radiant, so this appears to
be a different stream. The rates are very low, but the extreme slow
speed should allow identification.

AUC (August Capricornids), v19 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 12; RA 316 (21:04); Dec -02 (Start of Activity)
Aug 22; RA 306 (20:24); Dec -11 (Peak)
Aug 24; RA 304 (20:16); Dec -12 (End of Activity)

The next is the epsilon-Cassiopeiids (ECS) a radiant that runs parallel
to the Perseids. They may in fact be related, but the location is far
enough from the PERs that they can possibly be detected as a separate
shower. Since the rate is so low, there should be little effect on
Perseid ZHR calculations. Be sure to know exactly where the radiant is
if you are going to report this shower. I suggest contacting me (at
meteoreye-at-comcast.net) for an excel spreadsheet with the daily locations.

ECS (epsilon Cassiopeiids), v50 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 20; RA 042 (2:47); Dec +69
Aug 26; RA 035 (2:20); Dec +62 (Peak, shower ends the next night)

Next is the Pi-Draconids (PDR). This shower of medium speed (30 km/sec)
meteors is reasonably far from any other radiant, so could be teased
out. However, the rate would be very low.

PDR (pi-Draconids) v 30 km/sec
Date (UT); Right Ascension (Degrees, then Hours:Min); Declination
Aug 26; RA 293 (19:33); Dec +66 (Start of Activity)
Aug 27; RA 292 (19:26); Dec +65 (Peak)
Aug 31; RA 284 (18:57); Dec +60 (End of Activity)

Near the end of the August, a few other video showers pop up in the
data, but I’ve taken up enough space for this month’s NAMN notes, so
I’ll truncate the list here, and mention them next month. This includes
the Aurigids, and some minor video showers.


6.  Magnitude References...

It’s a good month to get a handle on the average meteor magnitudes.

In addition to Jupiter in the south, blazing at magnitude -2.6, Vega is
overhead at zero magnitude. Altair (in Aquila), Formalhaut, and Deneb
(in Cygnus) are 1st magnitude. In the morning sky, there are two
embedded triangles. Three 2nd magnitude stars surround Triangulum. They
are alpha Andromeda (the northeastern corner of the Great Square of
Pegasus), gamma Andromeda (at the end of the long arm), and alpha
Arietis, the brightest star in Aries. Right in between is Triangulum,
and those three stars are Magnitude +3, +3.5, and +4.

The month starts and ends with a New Moon, dark all night. The Full Moon
is just after the Perseid peak, so splits the month in half.


7. For More Information...

For radiant positions and more detailed descriptions of showers, see the
IMO 2008 Meteor Shower Calendar at:

http://www.imo.net/calendar/2008

For those who wish to look for other minor showers not listed here, or
want daily radiant positions for all the showers, drop me an e-mail at
my meteoreye address below, and I’ll send you my current Excel spreadsheet.

Feel free to contact us for questions and comments!!
-------------------------------------
NAMN email: namn at namnmeteors.org
NAMN website: http://www.namnmeteors.org

Mark Davis, meteors at comcast.net
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network

Wayne T Hally, meteoreye at comcast.net
High Bridge NJ
Writer, NAMN Notes

Lew Gramer, dedalus at alum.mit.edu
Homestead, Florida, USA
Coordinator, Public Outreach
Owner/Moderator, 'MeteorObs'

Kevin Kilkenny, namnfireball at earthlink.net
Staten Island, New York, USA
Coordinator, Fireballs and Meteorites

Back issues of NAMN Notes can be found online at the NAMN website and in
the MeteorObs archives at:
http://www.meteorobs.org by selecting 'Browse Archive by Month'

To subscribe to the meteor email list:
Contact Lew Gramer at: dedalus at alum.mit.edu

==============================================
Here's to 'Clear Skies' for August...

August 2008 NAMN Notes
Written by Wayne T. Hally & edited by Mark Davis
==============================================