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NAMN Notes: December 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

Headlines:
* Major Showers: Moonlit Geminids, Ursids Moon Free
* Winter’s Minor Showers
* Quadrantid Notes for 2009

1. Geminids Too Friendly with the Moon...
2. Moon Free Ursids...
3. Dark Skies to Investigate the Comae Berenicids...
4. Antihelion Radiant Returns...
5. Minor Showers of December...
6. 2009 Quadrantids...
7. Sky Notes...

As we have said too many times this year, the moon could hardly be in a worse position to observe this year’s Geminids. The Full Moon occurs at 1637 UT on the 12th, and the Geminid peak is just a day and a half later when the 97% illuminated moon has moved even closer to the radiant. On the peak night (23 UT Dec 13 - just after sunset for the eastern US) it is only about 20 degrees away. Scientific data will be very hard to come by unless skies are extremely clear and dry. Still, it never hurts to watch since there could always be a surprise.

The official IMO visual dates for the Geminids are from the 7th to the 17th. Video data shows possible activity as early as November 23rd, but this would be at a rate too low to be detected under the sky (less than a single meteor in 3 or 4 hours). It appears that by the 1st of December, careful observers that have experience estimating meteor velocity, and certainly using an alignment cord for counting or plotting, might be able to accurately identify some shower members.

The start of IMO visual period seems to show when the rate might exceed one or two an hour, still below that of the sporadics, but high enough to collect reliable data for most observers. On the 7th, the moon is setting around the time the radiant is rising, so much of the night should be moon free with low Geminid activity.

For the peak night (the 13-14 for North America) I really don’t have too many useful suggestions. The moon rises and sets right next to the radiant. Both are up during almost all night hours. If you block the moon, you block the radiant. This is one circumstance where an alignment cord really helps, since you can look at the darkest part of the sky, and almost use the moon as a reference point to see if the observed meteors backward prolongation aligns with the Geminid radiant, which is located very close to Castor (the highest of the twin stars); the moon is a small amount lower.

Estimating the limiting magnitude will be very difficult since the IMO polygonal count method is only useful with skies better than about magnitude +5. What I try and do is document the faintest stars I can see in my field of view, and then look them up afterward using my SkyMap program; you can always ask me for help.

As a minimum, you can make the polygon count, but they will provide only a very rough estimate, something like +/- a half or full magnitude. Still, if it’s clear, we might as well spend some time enjoying the show, and record data as accurately as we can.

Below are the radiant positions. I use the video positions from the 1st to 6th, then the IMO visual positions, and I extend it one day since the video data shows there may be a high enough rate, and the moon will be less of a problem. Not much less of a problem, but at least a little better than the peak night. For nights between, you can interpolate to determine the positions, as you should for any of the listed showers.

The Geminids are material from Phaethon 3200, which appears to be an asteroid, but is most likely a degassed comet nucleus. Were it not for the Geminids, it would be known only as an asteroid. It has a very short orbital period of only 1.59 year, and is about 5 km in diameter, and approaches the sun at a perihelion distance of only 0.14 AU, closer than any other numbered asteroid. As a result, the surface gets hot enough to melt rock, with temperatures possibly as high as 1025K (760 C, 1400 F)! For comparison, Mercury’s perihelion is 0.31 AU, twice as far away, and its surface “only” reaches 700K (425 C, 800F). It is currently visible in large scopes as a magnitude +17.7 object in Triangulum.

Phaethon claimed his father was Helios, though there are other stories in mythology suggesting dear old dad was Cephalus and mom was Eos. I prefer not to get into arguments with the Gods, so will just watch the meteors.

GEM - Geminids, velocity 35 km/sec (medium speed)

UT Date, RA (Deg, hh:mm), Dec
Dec 01   099 (6:38), +33
Dec 07   105 (7:00), +33 (Start of IMO Visual Shower)
Dec 14   112 (7:28), +33 (Geminid Peak)
Dec 19   119 (7:57), +32 (End of Visual Activity)

The Ursids (technically they should be called the Ursa Minorids) are visible in mostly moon free skies this year. This is a low rate (ZHR ~ 10) shower in most years, and could use some more observations to help define it. A few outbursts and higher activity levels have been noted in the last century, but many others may have been missed due to poor weather and busy lives. The parent object is comet 8P/Tuttle, first seen in 1790. It orbit is highly inclined with a period of 13.6 years. It was closest to the earth in early January 2008, so this could be a year with some enhanced activity.

According to the IMO visual working list, the radiant shows very little motion during the activity period 16-26 December. However recent video data, while in good agreement near peak morning of the 22nd, shows substantially different locations near the beginning and end of the period. Therefore I will list both the IMO working list positions as well as the video ones.

This shower requires you to face almost due north, since the radiant is near the bowl of the Little Dipper, so it will be difficult to monitor other showers at the same time. Since the radiant rises above 30 degrees elevation about midnight, you can spend some time before then gazing toward the south to observe the other active showers, then shift to north later on.

The predicted peak time is 0730 UT on the morning of the 22nd, very well placed for eastern North America (0230 EST). The thin crescent moon doesn’t rise until a bit later, and shouldn’t cause big problems. Of course as we have seen many times, meteor showers often choose to ignore the predicted peak time, so it’s worth investing a few hours. These meteors hit the atmosphere at 33 km/sec, quite comparable to the Geminids, but seem to be fainter. Now if we can just get the weather to cooperate!

URS - Ursids, velocity 33 km/sec (medium speed)

UT Date, RA (Deg, hh:mm), Dec
IMO Working List Positions
Dec 16   217 (14:28), +78   (Start of Activity)
Dec 22   217 (14:28), +75   (Peak ~ 0730 UT)
Dec 26   217 (14:28), +74   (End of Activity)

IMO Video Data Positions
Dec 16   201 (13:24), +76   (Start of Activity)
Dec 22   217 (14:27), +75   (Peak Morning)
Dec 26   227 (15:08), +74   (End of Activity) 

This shower has always been poorly observed, due to its occurrence during early and mid winter and its low rates. As a result, it appears that the true center of activity has been misaligned. Video records over the last decade have shown similar levels of activity (maximum ZHR ~ 5) to historical records, but place the radiant in a unique position, not matching the old IMO working list position, nor that of the IAU (shower #20).

The IMO has decided to deal with this adjustment period by asking that observers monitor both the older position (COM) and a new one (CBE). They are far enough apart that, if a proper field of view is chosen, it should be easy to assign meteors to one or the other. I will therefore list both positions. Please assign any meteors to one or the other and report them in that manner to the NAMN, and to the IMO if you report your data directly. These are swift meteors with a velocity of 65 km/sec so should stand out.

The peak occurs between the 20th and 30th of December, with steady rates throughout that period. Video data shows a slightly longer activity period, so I will include positions from earlier in December. This is a very long shower, with the last meteors showing up in early February.

COM - Comae Berenicids velocity 65 km/sec (Very Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 12   171 (11:22), +27
Dec 20   177 (11:48), +24
Dec 25   181 (12:04), +23
Dec 31   186 (12:23), +21
Jan 05   190 (12:39), +19

CBE - Comae Berenicids velocity 65 km/sec (Very Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 05   148 (09:54), +37
Dec 10   153 (10:12), +35
Dec 15   157 (10:28), +33
Dec 20   161 (10:44), +30  (Beginning of Peak Period)
Dec 25   166 (11:04), +28
Dec 31   171 (11:24), +26  (End of Peak Period)
Jan 05   175 (11:40), +24 

Rates from the Northern and Southern Taurids have declined to the point where it is time again to just assign meteors to the Antihelions (ANT). While video data shows the Northern Taurids maintain some activity, it is too low to be separated from the general Antihelion meteors. Remember, the radiant is large and elongated, 20 degrees in diameter along the ecliptic, and 5 or so degrees above and below the listed positions. These are medium speed meteors.

ANT - Antihelion Radiant, velocity 30 km/sec (Medium)

UT Date, RA (Deg, hh:mm), Dec
Dec 01   081 (5:24), +23
Dec 05   085 (5:40), +23
Dec 10   090 (6:00), +23
Dec 15   096 (6:24), +23
Dec 20   101 (6:44), +23
Dec 25   106 (7:04), +22
Dec 31   112 (7:28), +21

Two IMO working list minor showers are accessible from all of North America during December, while a third just peeks above the horizon for the southern US and Mexico.

The first to discuss is the sigma Hydrids (HYD) which have a ZHR around 3 near the Full Moon this year. As such, it will be hard to see the “peak”; it’s really more of a bump than a peak...

The IMO working list shows activity from the 3rd through 15th with a peak on the 12th, while recent IMO video data shows a longer period and an earlier maximum on the 9th. The last few nights before the Full Moon are likely to show the highest rates. After that time, while there will be moon free hours in the evening, the moon will be up when the radiant is, and they will be close to each other. Still, I will list the positions later in the month. These are fast meteors, between 58 and 60 km/sec. No parent object for this shower has been found.

HYD - sigma Hydrids, velocity 59 km/sec (Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 03   120 (8:04), +03  (Working List Start of Activity)
Dec 06   123 (8:13), +03
Dec 09   126 (8:23), +02  (Video Indicated Peak)
Dec 12   128 (8:32), +02  (Full Moon, Working List Peak)
Dec 16   132 (8:47), +02
Dec 21   136 (9:03), +01
Dec 27   141 (9:22), -01  (End of Video Indicated Activity)

The second shower has even a lower maximum rate, the Monocerotids (MON). It is associated with comet C/1917 F1 (Mellish), a long period (~ 145 year) comet. While the visual rate is quite low, there are a large number of photographic (and now video) meteors that show the shower is real.

Like the sigma Hydrids, the best time to see some will be the last few days before the Full Moon, when the shower peaks and there are some moon free hours toward dawn.

MON - Monocerotids, velocity 42 km/sec (Medium Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 01   092 (6:08), +08
Dec 05   096 (6:24), +08
Dec 09   099 (6:37), +08   (Peak Morning)
Dec 17   106 (7:02), +08   (End of Video Indicated Activity)

The third working list shower is the Puppid-Velids (PUP). It never even reaches an elevation of 20 degrees for anyone in the US or northern Mexico, so any data collected will not be very useful scientifically. At 40 degrees north, the radiants reach only 3 degrees above the horizon near 4AM local time. From more southern locations, it is strongly suggested that the meteors be plotted in order to extract the most value. In addition, there appear to be multiple radiants, with differing periods of activity. The IMO working list gives a position of RA 123, (9:12), Dec -45 for the peak night of Dec 6th with an activity period of the 1st to 15th. The velocity is 40 km/ sec, which is medium speed.

Among the newly confirmed video showers is the November Orionids (NOO), which continues through the period before the Full Moon whiteout. This radiant is located between that of the MON and GEM showers in December. These medium fast meteors need to be assigned with care since there isn’t much room in there. Rates would be expected to be quite low after the 5th.

NOO - November (omega) Orionids, velocity 45 km/sec (Medium Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 01   094 (6:16), +14
Dec 05   097 (6:28), +16
Dec 09   101 (6:43), +17 

Since the Quadrantids occur so soon after the start of the New Year, the shower starts before the end of this month, and it is a busy time with all the holiday festivities, I thought I’d at least give a heads up on what is expected next year, right around the time of the Earth’s perihelion. It’s the first meteor shower in the International Year of Astronomy, but the timing does not appear to be good for eastern North America, with the peak occurring during the daylight hours of January 3rd. However, the further west you are, the closer you are to the maximum time.

If the peak occurs as expected, our best chance to see a significant amount of Quads are during the early morning hours of the 3rd near dawn. Since the moon sets before midnight, it will not be a factor, and the radiant rises higher (thus increasing the percentage of the ZHR you can see) at the same time. Those last few hours before twilight seem to be the targeted time for us to bundle up and watch the sky. Rates the following morning, while low, would be expected to be better than those on the morning of the 2nd.

The video data suggests that some detectable Quadrantids continue beyond the IMO Visual dates (Jan 1-5) so I will list a later position as well. The agreement between the Working List and video data is excellent.

QUA - Quadrantids, Velocity 41 km/sec (Medium Fast)

UT Date, RA (Deg, hh:mm), Dec
Dec 31   228 (15:12), +50  (Start of Visual Activity)
Jan 03   230 (15:19), +49  (Peak Morning)
Jan 05   231 (15:24), +49  (End of Working List Activity)
Jan 08   233 (15:31), +48  (Last Morning with some Moon Free Time) 

Like most months this year, December is split by the Full Moon into 4 periods. There’s a week or so with moon free morning hours, a 5 or 6 day period with the near Full Moon up all the time, a week with evening moon free time, and the last week or so surrounds the New Moon where if you prepare for the weather you can watch all night long. As mentioned above, the Full Moon is nearly coincident with the Geminid peak. Things will be better next year!

Some reference stars (and planet) for estimating meteor magnitudes follow. I’ll list them in order from brightest to faintest. These are based on generally those visible around midnight at mid month, so should be in the sky most of the night.

Magnitude and object
-1.5 Sirius
+0.0 Betelgeuse (in Orion)
+0.1 Arcturus (in Bootes), Capella (in Auriga)
+0.2 Rigel (in Orion)
+0.4 Procyon (in Canis Minor)
+0.8 Aldebaran (in Taurus)
+1.0 Saturn (in Leo)
+1.2 Castor (in Gemini)
+1.4 Regulus (in Leo)
+1.6 Pollux (in Gemini), Bellatrix (upper right shoulder of Orion)
+1.9 Alhena (lower square leg of Gemini)
+2.0 Saiph (Lower left corner of Orion), Alphard (in Hydra, below head)
+2.1 Denebola (rear of Leo)
Stars in the sickle of Leo +2, +3.4, +3.9, +3.0
+3.1 epsilon Gem (pointed corner of LM area #4)
+3.6, +3.7 pair stars at eastern end of Taurus near Cetus
+3.9 star closest to Beehive Cluster
+4.1 star above and left of Rigel
Little Dipper +1.9 (Polaris), Bowl: +2.1, +3.0, +4.3, +5.0 

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

For assistance in understanding how to estimate limiting magnitude (the faintest stars you can see) the NAMN has a tool available here:

It’s especially helpful for those new to the process.

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 email: namn@namnmeteors.org
NAMN website: http://www.namnmeteors.org

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

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

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

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

Back issues of NAMN Notes can be found on-line 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 or to find out information on our weekly chat sessions:
Contact Lew Gramer at:
dedalus@alum.mit.edu