(meteorobs) NAMN Notes: September 2008

meteors at comcast.net meteors at comcast.net
Thu Sep 11 21:30:03 EDT 2008


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NAMN Notes: September 2008
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NAMN Notes is a monthly newsletter produced by the North American Meteor
Network. It is available both via email and on the NAMN website at
http://www.namnmeteors.org


Contents: Mostly Minor Showers, but good rates...

1. (AUR) alpha-Aurigids, No Outburst Expected This Year...
2. (SPE-DAU) Two Minor Showers on a Common Path...
3. (NTA-STA) The Taurids Spice Up the Antihelion Radiant...
4. (ERI-EER) Potential Activity from Eridanus...
5. Active Period for the Southern Apex Sources...
6. Showers Detected in Video Records...
7. Early Perseid Results...
8. For More Information...


1. (AUR) alpha-Aurigids, No Outburst Expected This Year...

The alpha Aurigid shower provides some activity in most years right
around the time we turn the page of the calendar from August to
September. The late summer showers in Aquarius, Capricorn and Cygnus
have ended, so it’s as if the meteor showers also turn the page at this
time. Last year, a predicted outburst of the AUR shower occurred close
to the scheduled time with a ZHR over 200 for about 15 minutes.

Nothing like that is expected this year, though it never hurts to watch.
This year, the peak is expected to occur with the New Moon, so there
will be no interference on that front. However, rates are expected to be
close to the normal of 7 per hour.

There is some conflict on the radiant position, so extra attention to
this issue would be appreciated. The IMO radiant position listed below
is in between two other suggested locations. This is about halfway
between Capella and the “bottom” of the limiting magnitude count area
number 17, the star theta Auriga.

The IAU position is nearly on top of theta, while IMO video observations
over the last decade have placed the radiant rather far away, actually
in Perseus, on the other side of the IMO position. Our best suggestion
is to use the IMO position listed below, but some note should be made of
meteors that would align better with the video radiant about 15 degrees
to the west.

I’ll list positions at the start and end of activity, as well as the
peak of Sept 1, and show the Sept 1 position from the other sources.

AUR alpha-Aurigids; velocity 66 km/sec
UT Date  RA (Degrees, Hr:Mm), Dec
Aug 25   076 (5:04),          +42 Start of Activity
Sep  1   084 (5:36),          +42 Peak of Activity (IMO Position)
Sep  8   090 (6:02),          +42 End of Activity

Sep  1   068 (4:32),          +48 Peak of Activity (IMO Video position)
Sep  1   090 (5:59),          +39 Peak of Activity (IAU Position)


2. (SPE-DAU) Two Minor Showers on a Common Path...

The September Perseids and delta Aurigids are two minor showers that
follow each other with a pronounced lull in between. The radiant drift
is the same and in the past they were considered one shower. However,
both IMO video data and IAU shower listings show them as two separate
showers, and IMO visual records show a substantial gap between them, so
they are now listed as back to back showers.

These are swift meteors with velocities of 64 km/sec. This year the
transition between the two showers takes place shortly after the Sept.
15 Full moon.

The IMO video data shows a different position and shorter periods for
both radiants, so I will list that as well. The IAU shower positions
agree with the video data for the SPE shower, and the IMO visual
position for the DAU showers.

Hopefully this situation will become clearer during the next year with
good visual and video observations. The DAU peak actually occurs in
early October, in fact video data only detects this shower after the end
of September. These showers are best observed during the early morning
hours as the radiant rises higher in the sky.

IMO Positions
SPE September Perseids; velocity 64 km/sec
UT Date  RA (Degrees, Hr:Mm), Dec
Sep  5   055 (3:40),          +46   IMO Visual Start of Activity
Sep  9   059 (3:56),          +47   IMO Visual Peak of Activity
Sep 16   068 (4:32),          +48  IMO Visual End of Activity

DAU delta Aurigids
Sep 17   069 (4:36),          +48  IMO Visual Start of Activity
Sep 24   076 (5:03),          +49
Sep 30   083 (5:32),          +49  Near New Moon

IMO Video Analysis Positions

SPE September Perseids; Velocity 61 km/sec
Sep  4   039 (2:36),          +39  Start of Activity
Sep  9   048 (3:10),          +39  Peak of Activity
Sep 13   054 (3:38),          +40  End of Activity


3. (NTA-STA) The Taurids Spice Up the Antihelion Radiant...

During September the Antihelion (ANT) radiant activity begins to ramp
up, and by the end of the month there is sufficient activity from both
the northern and southern branches to record activity separately. At
this point, the ANT designation is suspended and we call the showers the
Northern and Southern Taurids even though this early activity occurs
from southern Pisces. Both radiants are near the bottom of the “V”
between the two fish bracketing Pegasus higher in the sky during the
last few days of this month. Since they are only separated by about 6
degrees it can be difficult to determine which shower is the source of
some meteors, especially for ones that occur far from the radiants.

It’s the perfect time to break out an alignment cord; this really helps
a lot. When you see a meteor that comes from the Taurid radiants, hold
your cord up with one end over the meteor path, and the other near the
NTA and STA radiants; in most cases it should be easy to determine which
radiant was the source. If you do it by eye, the long backward
projection across the sky makes it much more difficult to assign the
meteor properly. Reporting the NTA and STA meteors individually provides
far more useful information than listing just Taurids. There is some
overlap between the radiants, so choosing a field of view somewhere
along the ecliptic (in Aquarius to the west in the evening, and in
Taurus to the east toward morning) will give you the best chance to
discriminate between the two sources. The STA velocity is given as 27
km/sec, the NTA as 29, comparable to the 30 km/sec for the ANT meteor
source. Both Taurid showers peak in early November, so we have plenty of
time to watch them! There are some predictions that this will be an
above average year, but only our observations can confirm that.

Below is the ANT radiant position through the start of the Taurids, then
the two Taurid radiants.

ANT Antihelion radiant (IMO ecliptic showers) velocity 30 km/sec
UT Date RA (Degrees, Hr:Mm), Dec
Sep  1   350 (23:20),        -03
Sep  6   356 (23:44),        -01
Sep 13   003 (00:12),        +02 (Last night before full moon)
Sep 19   009 (00:36),        +05 (First night after the full moon)
Sep 24   014 (00:56),        +07 (Last night of ANT radiant)

NTA Northern Taurids, velocity 29 km/sec
Sep 25   019 (1:16),         +11
Sep 30   022 (1:28),         +12

STA Southern Taurids, velocity 27 km/sec
Sep 25   021 (1:24),         +06
Sep 30   025 (1:40),         +07


4. (ERI-EER) Potential Activity from Eridanus...

Last month I reviewed the conflicting information about these showers.
The only portion active this month is the old IMO shower the ERI (pi
Eridanids). The IMO also listed in the past a shower called EER, but
since the radiant positions and velocity are nearly identical to that of
the ERI shower, it serves no purpose to call them by two different
names. These would be expected to be seen at low rates, but the fast
speed from such a low radiant does stand out.

ERI epsilon Eridanids NAMN positions

UT Date RA (Degrees, Hr:Mm), Dec
Sep  1   051 (3:23),         -15
Sep 13   057 (3:49),         -13


5. Active Period for the Southern Apex Sources...

Among the sporadic meteors, not all are true sporadics. There are
concentrations of meteors from specific areas in the sky. One is the
Antihelion sources along the ecliptic. It has a counterpart called the
Helion meteors, but since these come from the direction of the sun, very
few can be seen. Another is the Northern and Southern Toroidal meteors,
from material orbiting perpendicular to the plane of the solar system.
Finally there are the ecliptic Apex sources. These are meteors that we
run into nearly head on as we travel around the sun. Since they are near
the ecliptic, they also are separated by perspective and planetary
perturbations into northern and southern sources. A decade of IMO video
observations have fleshed out some detail, and shown that at some times
of the year there is more activity than normal from either the Northern
or Southern Apex radiants. During September, there are two such periods.
The first is from the 1st through 7th with a peak on the 5th, and the
second from the 15th through the 23rd with a peak on the 21st. Both of
these are from the Southern Apex radiant, and produce very low rates.
Still, it can be interesting to look for these fast meteors in the very
early morning hours. Since this is an annual source like the
Antihelions, it is best to use the single code SPX for these activity
periods throughout the year until any can be associated with a specific
parent body.

SPX Southern Apex; velocity 58-60

UT Date RA (Degrees, Hr:Mm), Dec
Sep  1   066 (4:24),         +02 Radiant between Orion and Taurus
Sep  5   066 (4:24),         +06 Peak
Sep  7   066 (4:24).         +08

Sep 15   071 (4:45),         +05
Sep 21   074 (4:55),         +08 Peak
Sep 23   075 (4:58),         +09 Radiant near Orion’s Shield


6. Showers Detected in Video Records...

A decade of IMO video observations has shown some evidence for a number
of low rate showers during this month. Two occur in Lynx, and one near
the end of the month in Orion. Since there are sparse showers, they are
best left for the experienced observer, hopefully using plotting or
photo/video observations.

SSL Southern September Lyncids; velocity 52 km/sec
UT Date RA (Degrees, Hr:Mm), Dec
Aug 31  111 (7:22),          +39   Peak
Sep  5  118 (7:50),          +31   End of Activity

NSL Northern September Lyncids; velocity 53 km/sec
Sep  8  097 (6:27),          +56   Start of Activity
Sep 12  112 (7:29),          +56  Peak of Activity
Sep 16  128 (8:32),          +56

AOR September alpha Orionids; velocity 59 km/sec
Sep 24  077 (5:08),          +07   Start of Activity
Sep 27  081 (5:24),          +07
Sep 30  085 (5:41),          +07


7. Early Perseid Results...

The Perseids provided a surprise outburst this year. It occurred a
number of hours after the predicted and observed peak, and corresponded
to the timing of the “tertiary” peak noted in Perseid returns in the
late 1990s.

The NAMN has so far received reports of 4,173 Perseids out of 8,057
total meteors during July and August in 383.5 Hours Teff from 28 observers.

Current NAMN totals for July and August can be seen here:

http://www.namnmeteors.org/observationsJulyAug08.html

An overview of ZHRs calculated using data submitted through the IMO’s
online form can be seen at:

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

It shows a peak using large bins of 117 +/- 2, and a narrow peak of 139
+/- 5 around 0200 UT on August 13th. So far over 25,000 Perseids have
been documented from almost 175 individuals worldwide.


8. 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 September...

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



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