(meteorobs) NAMN Notes: December 2008
meteors at comcast.net
meteors at comcast.net
Sun Dec 7 09:07:00 EST 2008
**************************
NAMN Notes: December 2008
**************************
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...
1. Geminids Too Friendly with the Moon...
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)
2. Moon Free Ursids...
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)
3. Dark Skies to Investigate the Comae Berenicids...
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
4. Antihelion Radiant Returns...
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
5. Minor Showers of December...
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
6. 2009 Quadrantids...
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)
7. Sky Notes...
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: http://www.imo.net/calendar/2008
For assistance in understanding how to estimate limiting magnitude (the
faintest stars you can see) the NAMN has a tool available here:
http://www.namnmeteors.org/lm_calc.html
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!!
-------------------------------------
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 December...
December 2008 NAMN Notes
Written by Wayne T. Hally & edited by Mark Davis
==============================================
More information about the Meteorobs
mailing list