(meteorobs) NAMN Notes: December 2007

[meteors at comcast.net]

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NAMN Notes: December 2007
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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:
1. Highlight of the Month/Year: The Geminids...
2. Other Major and Minor Showers of December...
3. Antihelion Radiant Returns...
4. COM and MON Expanded Discussion...
5. Don’t Miss the Quadrantids...
6. Data Sources and Contacts...


1. Highlight of the Month/Year: The Geminids...

“It is told that when young Phaethon, born from the God Apollo and a
mortal mother in Ethiopia, was given one wish by his father, he chose to
ride the Sun chariot. Unable to handle the steeds, he scorched what is
now the Sahara. To prevent more harm, he was shot down by Zeus. He fell
to his end like a meteor.”

 From Peter Jenniskens, in “Meteor Showers and their Parent Comets,”
reporting what Fred Whipple had written.

If you want to see a lot of meteors, no other shower during the year
provides a better opportunity than the Geminids. There are several
reasons for this, which I will explain. If you are willing to put in the
time, and have good weather, there’s no reason you can’t collect 500 or
even a thousand meteors in a single night! The story above does have
some basis in the facts of this shower, as both asteroid 3200 Phaethon
and the Geminid meteors come close enough to the sun (0.14 AU - well
inside Mercury’s orbit) to suffer significant heating, perhaps melting
both the surface of the former comet, and the meteoroids that we enjoy
each December.

First of all, the Geminids and Quadrantids (coming up during the first
few days of 2008) have the highest ZHR of the current annual showers,
around 120 per hour. Many people think that the Perseid’s rate is as
high, but since the turn of the century, without outburst enhancement,
this favorite shower of summer only has produced ZHR’s of about 100. So
all other things being equal, the Perseids would give a lower rate. In
addition, three factors benefit the Geminids. One is the longer nights.
During the Perseid peak, there are fewer hours of darkness than there
are now near the winter solstice. Another is the hazy skies in August,
which hide many fainter Perseid meteors. Finally, the Perseids, like
other major showers, have radiants that are best placed right before
dawn, whereas the Geminids are an “all night long” shower.

So let’s examine each of these in turn. Longer nights allow you to see
more meteors for showers with comparable rates. The Perseids occur in
mid August, when there are 7 to 10 hours of darkness across the
continent; during the Geminids, there can be 12 hours or more across the
north. So that means there can be 50% more hours to observe.

Especially in the eastern US, August is often dominated by hazy skies,
laden with humidity. This exacerbates the problem of light pollution, as
the moisture throughout the atmosphere provides a surface to reflect the
light. In mid December, the air is usually drier, and in theory should
provide darker skies.

Finally, there is the position of the radiant in the sky. Unlike the
other three major showers (Perseids, Orionids, and Leonids), the Geminid
radiant rises early and spends most of the night high in the sky.
Because the other three showers are debris from retrograde comets (that
orbit the sun in the opposite direction from 98% of everything else in
the solar system, including the earth), we hit them head on in the early
morning hours. That also means that the radiant does not rise until late
in the evening and doesn’t reach 30 degrees elevation until after
midnight. The Geminids’ parent, 3200 Phaethon, is in an orbit that is
prograde.

Why is 30 degrees elevation important? That is the height that, if you
are under perfect skies (LM +6.5), you should see half of the ZHR. So if
the ZHR at that time is 100, you would see 50 an hour. Of course, the
worse your Limiting Magnitude (LM) is, the fewer you will see.

The Geminid radiant rises just after sunset, even before the sky gets
dark, and the highest elevation in the south is around 2 AM. This year,
the moon will be setting just about the time the radiant reaches 30
degrees, so conditions couldn’t be much better.

The Geminids are active from December 7th through the 17th, according to
the IMO Working List of Meteor Showers. Recent video data suggests a
longer period of activity, from November 30th to the 18th of December,
so keep your eyes open. The radiant begins the month just above Mars,
and is near Castor (the higher of the Geminid twins) for the peak nights.

The peak is timed to occur around 1645 UT on the 14th (11:45 AM EST,
8:45 AM PST). Unfortunately, that’s daytime for North America. It
appears after that peak there is a small dip, then another lower peak of
activity about 3 hours later. If you have to pick one night, it would
appear that the night of the 13-14 (Thursday night/Friday morning) of
December would be the better one, since like most showers, the drop off
after the peak time is much more rapid than the rise in rate before the
peak. However, the nights before and after should provide entertaining
levels of activity. The Geminids often appear to have a color different
from most major showers. I’ll leave that discussion for next month after
everyone has made their own observations.

There is one other item of note. Models predicting the evolution of this
shower by J. Jones and R.L. Hawkes suggest that by 2050 the Geminid ZHR
may reach 190 per hour before declining in later years, making it the
dominant meteor shower of our century. Might as well make friends with
it this year!


2. Other Major and Minor Showers of December...

The next major shower we would usually discuss is the Ursids (URS),
technically, the Ursa Minorids. But this year, the Moon puts the hammer
down on them. With the full moon on December 24th, and the shower peak
(~10/Hr) on the 22nd or 23rd, there’s not much we can see. The radiant
is near the bowl of the Little Dipper. See the IMO shower location chart
referenced below if you feel you can try, 2 days before Christmas. The
total activity period is from the 17th to the 26th, with very low rates
except for the peak night. The radiant only reaches useful elevations
toward morning.

Minor showers...

Beside the Geminids and Ursids, there are a few minor showers that we
can look for. These are not showers that the casual observer should
worry too much about, since accurate assignment of these meteors
requires some experience, both in accurately determining the radiant,
and estimating the appropriate speed of the meteor. That is even truer
this year, now that our knowledge of shower activity is increasing every
day.

For these showers I have listed the start, peak, and end of activity
using the official IMO data, as well as IMO video records compiled by
Sirko Molau (SM).

PUP (Puppid-Velids) - This is a shower that may have a few different
radiants in the vicinity active over a period of two weeks. For North
America, there’s not much to see here. A ZHR of ~ 10 would only produce
an hourly rate of one an hour at 40 degrees north; even at Key West, the
radiant only reaches an elevation of 20 degrees near 3 AM. This would
lead to a rate of possibly 3 per hour for an hour or two if you are
observing under skies as dark as LM +6.5. This shower has not been
confirmed by video records. If you wish to record data, please be sure
to accurately determine the radiant position for the time of night you
are observing. These are medium speed meteors (40 km/sec) that will rise
from near the horizon in the early morning hours.

Start of Activity Dec 1: Radiant RA 120 (8:02) Dec -45
Peak Activity? Dec 7: Radiant RA 123 (8:13) Dec -45
End of Activity Dec 15: Radiant RA 128 (8:32) Dec -45

HYD (sigma Hydrids)- This is a low rate (ZHR 3) shower which reaches 30
degrees elevation around midnight, and reaches the highest elevation in
the south (transit) about 3:30 AM. These are fast meteors (58 km/sec).
IMO video observations (SM) suggest activity continues until Dec 24, so
I have included later radiant positions until the near Full Moon interferes.

Start of Activity Dec 1: Radiant RA 118 (7:54) Dec +01
Peak of Activity Dec 12: Radiant RA 128 (8:32) Dec +02
End of Activity (IMO) Dec 15: Radiant 130 (8:40) Dec +01
End of “Moonth” (SM) Dec 21: Radiant 137 (9:10) Dec -00

COM (Coma Berenicids) - The Coma Berenicids situation has become both
clearer and muddier at the same time. Recent visual observations have
indicated a later peak for this weak shower (Dec 29 vs. Dec 20), and
video observations have suggested a number of nearby radiants that could
be easily confused. For this section, I will list the IMO positions of
the shower at the start, and the old and new peaks (ZHR~5). These
positions are what should be reported to the IMO and NAMN as COM. See
the expanded COM discussion below for other radiants of interest. These
are very fast meteors (65 km/sec) from a position close to the Apex (the
direction the earth is moving in its orbit).

Start of COM activity Dec 12: Radiant RA 171 (11:22) Dec +27
Old IMO Activity Peak Dec 20: Radiant RA 177 (11:48) Dec +24
New IMO Activity Peak Dec 29: Radiant RA 184 (12:17) Dec +21
End of COM Activity Jan 23: Radiant RA 204 (13:38) Dec +12

MON (Monocerotids)- This is a weak shower with a peak ZHR of only 2 per
hour, with medium speed meteors around 42 km/sec. It begins in November,
but continues until December 17th. Below are IMO positions. See the
expanded MON discussion below. The radiant is to the “left” of Orion for
North American observers.

Start of Activity Nov 27: Radiant RA 088 (5:52) Dec +08
Peak of Activity Dec 9: Radiant RA 099 (6:37) Dec +08
End of Activity Dec 17: Radiant RA 106 (7:02) Dec +08


3. Antihelion Radiant Returns...

ANT (Antihelion radiant)- Once the end of November comes, the enhanced
activity of the Northern and Southern Taurids subsides, and we begin
reporting the meteors as ANT. In previous years, this shower was called
XOR (chi Orionids) but with the realization that this really represents
the daily motion of the meteors in the plane of the solar system
catching up to us from behind continuously throughout the year, we now
use the ANT designation. In fact the center of the radiant never crosses
onto Orion! As with all of these showers, there are actually two
radiants, one above and one below the ecliptic; the positions given are
for the center so each is 3 degrees higher or lower; the southernmost is
close to chi-Orion 1 and 2. However, since the activity level is so low
it is better to just make the radiant diameter larger than most showers
and group them together. The ZHR is close to 3, and these are on the
slow side, about 30 km/sec.


4. COM and MON Expanded Discussion...

COM - The knowledge obtained during the past decade of video
observations, combined with previous photographic records and the sparse
visual coverage during late December and January has been both a
blessing and a curse. This is particularly acute with these two showers.
In fact, this is the reason why this month’s NAMN Notes is a few days
late, as I have wrestled with how to present this information in a
useful and coherent manner. I apologize for the delay, since I
underestimated the difficulty. For the casual observer, this is of small
consequence, but for the few people who observe during these winter
months, I wanted to provide the most accurate and current data possible.
Typically, less than 2 dozen hours of Teff are reported between the end
of the Geminids and the end of January.

The video data has suggested a much more complicated situation. In fact,
for 2008, in addition to shifting the peak date later in the month of
December, the IMO says “The radiant ephemeris of this shower is severely
questioned after the scrutinization of single-station video data showing
a clear radiant with an offset of about 15 degrees to the Working List
positions.” The result is given as “possible COM” in the 2008 shower
calendar. The IMO recommends the use of the old COM positions for
2007-2008, while meteors from the “possible COM” position should be
noted separately.

This means that for IMO reporting, the COM positions listed in the minor
shower section above should be used. As to how you should report the
meteors to the NAMN, I will discuss that for each of the possible COM
radiants below.

The video data suggests there are actually 4 radiants nearby. I’ll
discuss the two radiants in December below, based on the start date of
activity. All of these showers produce fast meteors, between 58 and 64
km/sec.

The first is Sirko Molau’s shower 76. My research has indicated that the
positions are nearly a perfect match for IAU shower #32, the December
Leo Minorids (DLM). It is almost 20 degrees offset from the IMO’s COM
radiant, so they should not be counted as COM meteors. Meteors from this
radiant should be reported directly to the IMO as SPO, with comments
indicating they are DLM, which is “possible COM”. This shower produced
an outburst on December 5, 1921 of greater than 80 per hour. Since it
seems likely this stream is from a long period comet (possibly C/1798 X
1 Bouvard, per Jenniskens?), and this was the only outburst, it’s hard
to predict what might occur in coming years.

If you depend on the NAMN to forward your data to the IMO, that is what
will happen. In the NAMN database, they will be recorded as DLM, and
will be reported to the IMO as SPO with an explanation. This procedure
also applies to the other showers listed below. Here are the radiant
positions:

Start of DLM “possible COM” Activity Dec 4: Radiant 149 (9:54) Dec +35
End of DLM “possible COM” Activity Dec 29: Radiant 169 (11:14) Dec +28

The second is Sirko’s shower 81, which comes closest to the official IMO
position. In fact, on the video indicated peak date (Dec 16) the
radiants are identical. However on earlier days there is a considerable
offset, on the 9th there is an 11 degree difference in Declination.
These should be reported to the IMO and NAMN as COM. It would be worth
noting which position of the radiant (official IMO or Sirko Molau’s)
appears to be more accurate in describing the activity

(SM) COM Start of Activity Dec 9: Radiant RA 152 (10:06) Dec +23
(SM) COM End of Activity Dec 16: Radiant RA 174 (11:36) Dec +26

The other two video indicated showers occur in January, so we will
discuss them next month.

MON — Like the Coma Berenicids, the situation with the Monocerotids
after including recent video data has changed. It appears that in
addition to the standard MON radiant, there is another stream about 15
degrees away. Based on my research, this seems to be IAU shower #250,
the November omega Orionids (NOO). These were also reported as lambda
Orionids (LOR) but with as much evidence as there is for the NOOs, they
should be grouped together. This shower ends abruptly on December 5th,
when the standard MON radiant suddenly begins, missing the ascending
branch of activity. They should be reported to the IMO as SPO, with an
explanation that they are NOO in the comment section. That is how the
NAMN will forward the data.

(SM) NOO Activity this “Moonth” Nov 28: Radiant RA 091 (6:03) Dec +16
(SM) NOO End of Activity December 5: Radiant RA 096 (6:26) Dec +16

See the Minor shower section above for MON positions throughout this period.

I know this is rather technical stuff for many readers, feel free to
skim over this information. The situation with Major showers is easy to
figure out.

These Minor showers, with rates just above the visual threshold are a
challenge to see, but can teach us much about the evolution of meteor
streams. For the few dedicated observers who brave winter’s chill to
observe, I felt a need to provide all the things I have learned in my
research. For all the positions listed above, you can extrapolate
between the positions listed, or you can send me a message, and I will
send you detailed information of radiant positions for any night.
Ideally, future video and visual plotted observations will shed light on
these showers. If nothing else, it shows the value of accurately
determining the path of any meteor from these areas of the sky. That’s
more support for my suggestion last month of using an alignment string
for this purpose.


5. Don’t miss the Quadrantids...

I wanted to briefly mention January’s Quadrantids (QUA). This shower is
active from the 1st to the 5th, with this year’s peak expected at 0640
UT (1:40 AM EST) on January 4th. The moon is no threat, so it should be
fun. I promise that the January NAMN notes will come out early, to
provide all the latest information so we all can enjoy this high rate
shower, weather permitting.


6. Data Sources and Contacts...

For reference, here are the magnitudes of some objects you might
encounter during your night. Planet magnitudes are based on the night of
the New Moon, December 9th:

Venus, Magnitude -4.2, rising in Virgo in the predawn hours.
Mars, Magnitude -1.8, in Gemini, is visible all night long.
Sirius, Magnitude -1.4
Betelgeuse and Rigel, ~0 Magnitude in Orion.
Saturn, Magnitude +0.7 in Leo, rising in the late evening.
Castor and Pollux, the twins of Gemini Magnitudes are +1.2 and +1.6.
The other bright star at the opposite corner of Gemini from Castor,
gamma Gem is magnitude +1.9.
A good Magnitude 3 reference star is epsilon Leo, the brightest star in
the “sickle”.
The 5 stars that make up the “head” of Hydra are Magnitudes +3.1, +3.4,
+4.1, +4.3, and +4.5
	
For radiant positions and more detailed descriptions of showers, see the
IMO 2007 Meteor Shower Calendar at:  http://www.imo.net/calendar/2007

For comments and questions, you may contact us at the addresses below.

Happy observing!!



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

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Here's to 'Clear Skies' for December...

December 2007 NAMN Notes
Written by Wayne T Hally & edited by Mark Davis
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