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
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...
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)
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
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
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
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
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
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.
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!!
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NAMN website: http://www.namnmeteors.org
Mark Davis, firstname.lastname@example.org
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network
Wayne T Hally, email@example.com
High Bridge, NJ
Writer, NAMN Notes
Lew Gramer, firstname.lastname@example.org
Homestead, Florida, USA
Coordinator, Public Outreach
Staten Island, New York, USA
Coordinator, Fireballs and Meteorites
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