Meteor Activity Outlook for December 19-25, 2009

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

No matter where you live, the first half of December provides some of the best meteor activity of the year. In the northern hemisphere the sporadic rates are still strong plus you can also count on strong activity from the Geminids, which peak on December 13. There are also several minor radiants that add a few meteors each hour. All of these centers of activity are located high in the sky during the early morning hours this time of year. Unfortunately this year the bright moon spoils the show during the first week of the month. During the second week of December the moon will pass its last quarter phase and will not be such a nuisance .

As seen from the southern hemisphere the sporadic rates are increasing toward a January maximum. Shower rates are also good but the Geminids suffer a bit from the lower elevation seen from southern locations. Still with the warmer weather now occurring south of the equator, December is a great time to view celestial fireworks.

During this period the moon reaches its full phase on Thursday December 31st. On that date the moon lies opposite the sun and is in the sky the entire night. This weekend the waxing gibbous moon sets during the early morning hours allowing a couple of hours of viewing in dark conditions before the onset of morning twilight. The estimated total hourly rates for evening observers this week is ~3 no matter your location. For morning observers the estimated total hourly rates should be ~20 from the northern hemisphere and ~15 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Rates are reduced this week due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning December 26/27. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following showers are expected to be active this week.

Antihelions (ANT)

Now that the activity from particles produced by comet 2P/Encke has ceased encountering the Earth, the Taurid showers for 2009 are over and we resume reporting activity from the Antihelion radiant. This is not a true radiant but rather activity caused by the Earth’s motion through space. As the Earth revolves around the sun it encounters particles orbiting in a pro-grade motion that are approaching their perihelion point. They all appear to be radiating from an area near the opposition point of the sun, hence the name Antihelion. These were once recorded as separate showers throughout the year but it is now suggested to bin them into their category separate from true showers and sporadics. This radiant is a very large oval some thirty degrees wide by fifteen degrees high. Activity from this radiant can appear from more than one constellation. The position listed here is for the center of the radiant which is currently located at 07:12 (108) +22. This position lies in central Gemini, 2 degrees west of the fourth magnitude star Delta Geminorum. Since the radiant is so large, Antihelion activity may also appear from eastern Taurus, northeastern Orion, western Cancer, or southern Auriga. This radiant is best placed near 0100 local standard time (LST) when it lies on the meridian and is highest in the sky. Rates at this time should be ~3 per hour as seen from the northern hemisphere and ~2 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow speed.

Alpha Hydrids (AHY)

Activity from the Alpha Hydrids (AHY) begin to appear on the morning of December 30th. This shower reaches maximum activity on the 31st from a radiant located at 08:24 (126) -08. This position lies in extreme western Hydra, 15 degrees west of the second magnitude star Alphard (Alpha Hydrae). These meteors are best seen near 0200 LST when the radiant lies highest above the horizon. Due to the intense moonlight present at maximum, hourly rates from this shower will be < 1 per hour no matter your location. At 45 km/sec. the Alpha Hydrids produce meteors of medium velocity.

December Leonis Minorids (DLM)

The December Leonis Minorids (DLM) are active from a radiant located at 11:10 (168) +27. This position lies in a blank area of the sky where the borders of Leo Minor, Leo, and Ursa Major meet. The nearest bright stars are Nu and Xi Ursae Majoris which lie 5 degrees to the northeast. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. This shower peaked on December 20th so current rates would be ~2 per hour as seen from the northern hemisphere and < 1 per hour as seen from south of the equator. At 64 km/sec. the December Leonis Minorids produce mostly swift meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see ~15 Sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be ~2 per hour. As seen from the mid-southern hemisphere (45S), morning rates would be ~12 per hour as seen from rural observing sites and ~2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening rates are reduced this week due to moonlight.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week long.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
ANT Antihelions          07h 12m  +22    30     3     2
AHY Alpha Hydrids        08h 24m  -08    45    <1    <1
DLE Dec Leonis Minorids  11h 10m  +27    64     2    <1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Dec 22/23 Meteors

A relatively strong (at least for AZ) storm moved through the region over the past few nights. Similar to the storm from a few weeks back, one of my cameras again suffered from condensation in its lens. The problem is not the lenses but my all-weather enclosure which is no longer “all-weather”. For the time being, I’ll be down to a single camera again until after the holidays when I’ll have time to fix the faulty enclosure.

The aforementioned storm shut me out for a 2nd straight night. Luckily the storm had moved far enough to the east to allow Bob to get some good data.

Bob’s notes from the night of Dec 22/23 : “Clouds and rain prevented any useful video observations on the 22nd, which was bad timing as this was the maximum night for the Ursid meteor shower. The skies cleared near midnight last night and remained clear the remainder of the morning. Meteor rates varied significantly without any rhyme or reason. No Ursids remained from the maximum that occurred the previous morning.”

Due to the holidays, postings will be sparse. If anything exciting happens I’ll put something out. Until then, Merry Christmas and Happy New Year!

Obs  Date(UT)      Time    TOT SPO ANT DLM URS
TUS  2009-12-23   00h 00m  No meteors - Clouds/Rain
SDG  2009-12-23   05h 42m   43  36  4   3   0 

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
DLM - December Leonis Minorids
URS - Ursids

Dec 18/19/20/21/22 Meteors

The “big” meteor story for this week is the peak of the Ursids. Scheduled for last night the Ursids are not considered a major shower but can often produce rates as high as 10-15 per hour. On occasion they can do much better. Unfortunately Arizona was socked in last night and my systems didn’t detect a single meteor.

Salvador Aguirre was able to observe a few Ursids visually 2 nights before the predicted peak (Dec 19/20). From Hermosillo, Salvador was able to detect 34 meteors in ~2 hours of observing under a sky with a limiting magnitude of +6.40. Of those 34 meteors, 10 were Ursids, 10 were Coma Berenicids, 6 were December Leonis Minorids, 2 were Antihelions, and 6 were Sporadics.

Bob’s notes from the night of Dec 18/19 : “The cloud cover was not as bad as the previous night but still reduced rates by roughly half. The Coma Berenicids finally came to life last night producing 5 shower members.”

… and for the night of Dec 19/20/21 : “High clouds severely compromised observing sessions the past two nights. It does not appear the weather will improve before the Ursid maximum on December 22.”

Obs  Date(UT)      Time    TOT SPO ANT HYD MON DLM COM URS
TUS  2009-12-19   12h 12m   36  18  4   5   2   4   0   3
SDG  2009-12-19   12h 04m   39  25  5   2   0   2   5   0
TUS  2009-12-20   12h 11m   33  16  2   3   2   7   3   0
SDG  2009-12-20   12h 03m   19  13  3   1   -   2   0   0
TUS  2009-12-21   02h 57m   9   7   1   0   -   1   0   0
SDG  2009-12-21   11h 11m   9   7   0   -   -   2   0   0
TUS  2009-12-22   00h 00m   No Meteors - Clouds all night
SDG  2009-12-22   00h 00m   No Meteors - Clouds all night

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
HYD - Sigma Hydrids
MON - Monocerotids
DLM - December Leonis Minorids
COM - Coma Berenicids
URS - Ursids

Meteor Activity Outlook for December 19-25, 2009

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

No matter where you live, the first half of December provides some of the best meteor activity of the year. In the northern hemisphere the sporadic rates are still strong plus you can also count on strong activity from the Geminids, which peak on December 13. There are also several minor radiants that add a few meteors each hour. All of these centers of activity are located high in the sky during the early morning hours this time of year. Unfortunately this year the bright moon spoils the show during the first week of the month. During the second week of December the moon will pass its last quarter phase and will not be such a nuisance .

As seen from the southern hemisphere the sporadic rates are increasing toward a January maximum. Shower rates are also good but the Geminids suffer a bit from the lower elevation seen from southern locations. Still with the warmer weather now occurring south of the equator, December is a great time to view celestial fireworks.

During this period the moon reaches its first quarter phase on Thursday December 24th. On that date the moon lies ninety degrees east of the sun and sets near midnight local standard time (LST). This weekend the waxing crescent moon will set during the evening hours and will not cause any interference during the more active morning hours. The estimated total hourly rates for evening observers this week is ~3 no matter your location. For morning observers the estimated total hourly rates should be ~20 from the northern hemisphere and ~15 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Rates are reduced during the evening hours this week due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning December 19/20. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following showers are expected to be active this week.

Antihelions (ANT)

Now that the activity from particles produced by comet 2P/Encke has ceased encountering the Earth, the Taurid showers for 2009 are over and we resume reporting activity from the Antihelion radiant. This is not a true radiant but rather activity caused by the Earth’s motion through space. As the Earth revolves around the sun it encounters particles orbiting in a pro-grade motion that are approaching their perihelion point. They all appear to be radiating from an area near the opposition point of the sun, hence the name Antihelion. These were once recorded as separate showers throughout the year but it is now suggested to bin them into their category separate from true showers and sporadics. This radiant is a very large oval some thirty degrees wide by fifteen degrees high. Activity from this radiant can appear from more than one constellation. The position listed here is for the center of the radiant which is currently located at 06:44 (101) +23. This position lies in
central Gemini, two degrees south of the third magnitude star Epsilon Geminorum. Since the radiant is so large, Antihelion activity may also appear from eastern Taurus, northeastern Orion, or southern Auriga. This radiant is best placed near 0100 local standard time (LST) when it lies on the meridian and is highest in the sky. Rates at this time should be ~3 per hour as seen from the northern hemisphere and ~2 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow speed.

December Leonis Minorids (DLM)

The December Leonis Minorids (DLM) are active from a radiant located at 10:46 (162) +31. This position lies in eastern Leo Minor, approximately 8 degrees northeast of the third magnitude star Zeta Leonis. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. This shower peaks on December 20th so current rates would be ~2 per hour as seen from the northern hemisphere and < 1 per hour as seen from south of the equator. At 64 km/sec. the December Leonis Minorids produce mostly swift meteors.

Coma Berenicids (COM)

The Coma Berenicids (COM) are active from a radiant located at 11:48 (177) +18. This position actually lies in eastern Leo, 3 degrees north of the second magnitude star Denebola (Beta Leonis). These meteors are best seen near 0600 LST when the radiant lies highest above the horizon. This shower peaked on December 16th so current rates would be ~1 per hour no matter your location. At 65 km/sec. the Coma Berenicids produce mostly swift meteors.

Ursids (URS)

The Ursids (URS) peak on December 22 with an average ZHR of 10. The location of this radiant on that morning is 14:32 (218) +75. This area of the sky is located in southern Ursa Minor, close to the orange second magnitude star Kochab (Beta Ursae Minoris). This area of the sky is circumpolar (never sets) for most of the northern hemisphere. While activity may be seen during the entire night, these meteors are best seen during the last dark hour before dawn when the radiant lies highest above the horizon. Due to the high northern declination (celestial latitude), this shower is not visible to observers located south of the equator. At 33 km/sec. the Ursids will usually produce meteors of medium to slow velocity. To read more on viewing the Ursid shower visit the AMS website at: http://www.amsmeteors.org/showers.html#ursids

As seen from the mid-northern hemisphere (45N) one would expect to see ~15 Sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be ~2 per hour. As seen from the mid-southern hemisphere (45S), morning rates would be ~12 per hour as seen from rural observing sites and ~2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening rates are reduced this week due to moonlight.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week long.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
ANT Antihelions          06h 44m  +23    30     3     2
DLE Dec Leonis Minorids  10h 46m  +31    64     2    <1
COM Coma Berenicids      11h 48m  +18    65    <1    <1
URS Ursids               14h 32m  +75    33    <1     0

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Dec 15/16/17/18 Meteors

Meteor rates continue to be elevated. Though the Geminids are now history for 2009, a number of minor showers are displaying an impressive amount of activity. In particular, the December Leonis Minorids are producing between 10 and 25% of the nightly total. It will be interesting to see if this shower remains active over the next few days.

From Bob’s note for the night of Dec 15/16 : “There was scattered cirrus at dusk last night. Conditions were still good enough for video observations. Unfortunately conditions quickly deteriorated and thicker cirrus prevented the recording of any activity between 0400 and 0900 UT (8pm-1am PST). Conditions improved during the remainder of the morning allowing the recording of some activity before dawn arrived.”

… for the night of Dec 16/17 : “The cirrus was less widespread than yesterday. It was more prevalent during the evening hours and then cleared during the morning hours. It’s puzzling to see the dip in rates between 11-12 UT when it was mostly clear. It’s also surprising not to see any Antihelions prior to midnight, as the radiant is high in the sky.”

… and for the night of Dec 17/18 : “The cirrus clouds were back tonight with vengeance. It was mostly cloudy until 11UT (3am PST). The next hour seemed to be totally clear and then clouds interfered again the next hour. The last 46 minutes had mostly clear skies again. The new “COM’s” have been a disappointment. They are supposed to be slightly weaker than the “DLM’s” but the difference to me is striking with the “DLM’s” being the far stronger shower. Note that my first Ursid was detected tonight.”

Obs  Date(UT)      Time    TOT SPO ANT GEM HYD MON DLM DAD COM URS
TUS  2009-12-18   12h 12m   36  13  2   -   5   4   9   -   2   1
SDG  2009-12-18   11h 55m   33  23  4   -   2   1   2   -   0   1
TUS  2009-12-17   12h 12m   48  29  2   0   1   1   9   -   3   2
SDG  2009-12-17   12h 00m   64  47  4   -   4   1   7   -   1   0
TUS  2009-12-16   12h 06m   13  4   2   3   2   0   0   -   2   -
SDG  2009-12-16   11h 58m   32  23  2   2   1   1   2   1   0   -

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
MON - Monocerotids
DLM - December Leonis Minorids
DAD - December Alpha Draconids
COM - Coma Berenicids
URS - Ursid

Dec 13/14/15 and the Peak of the Geminids

Sunday night marked the predicted peak of this year’s Geminid meteor shower. Observers from around the world submitted observations to the International Meteor Organization. These observations showed that a possible double peak was observed on Dec 13 at ~18 UT and on Dec 14 at ~1 UT. At its best the Geminids produced ~130 meteors per hour (assuming a dark site where stars as faint as magnitude 6.5 could be seen and the radiant was overhead). The measured peak rate may change with further analysis. If the ZHR of 130 per hour holds then this year’s Geminids were pretty much as strong as predicted. Some predictions called for the peak to occur on Dec 14 at 5 UT so the actual peak was a few hours early.

The 2 graphs below are from the International Meteor Organization. The first shows the hourly rate of Geminids for the past 11 nights. The 2nd focuses on the peak of activity.

Graph of Geminid ZHR rates as determined from data submitted to the IMO. Credit: International Meteor Organization
Graph of Geminid ZHR rates centered on the time of the peak. Credit: International Meteor Organization

Here in Tucson something other than meteors was falling from the sky. The clouds and rain kept me from observing. Still I left my 2 cameras on and they were able to detect 7 meteors between the clouds. This is the 2nd year in a row that the Geminids have been clouded out for Tucson. Not too far to the south of Tucson in Hermosillo, Salvador Aguirre had better luck. On the night of the peak he observed 33 Geminids. Even better was his tally for the night before the peak when he observed 260 Geminids including 21 Geminids seen in a single 15 minute span.

Last night the sky was clear once again though Geminid activity has greatly decreased from the night before. 2010 will be another great year for the Geminids. Though the Moon will be a problem until around midnight. After that the sky will be nice and dark.

From Bob’s note for the night of Dec 14/15 : “After a week of clouds and rain the sky finally cleared. There was still a thin layer of high clouds which seemed to affect the sporadic count more than any of the showers. At 11:51:20 UT (3:51:20 am PST) a Sigma Hydrid fireball estimated at magnitude -7 was captured in the northeastern sky passing just east of the Big Dipper.”

A -7 magnitude Sigma Hydrid from Bob Lunsford camera on Dec 15 @ 11:51:20 UT. Credit: Bob Lunsford

Obs  Date(UT)      Time    TOT SPO ANT GEM HYD MON PUP DAD DLM COM
TUS  2009-12-15   12h 07m   58  23  2   18  6   0   0   1   7   1
SDG  2009-12-15   12h 00m   71  33  6   16  5   2   0   0   7   2
TUS  2009-12-14   02h 17m   7   2   1   4   0   0   0   0   0   0

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
MON - Monocerotids
PUP - Puppids/Velids 
DAD - December Alpha Draconids
DLM - December Leonids Minorids
COM - Coma Berenicids

Dec 11/12/13 Meteors

The Geminids peak for 2009 is now upon us. The peak is scheduled for around 5 UT tonight (Sunday night). That works out to about midnight EST and 9 pm PST. The peak is not very sharp so rates will be good all night long. In fact for western observers, there will be very few meteors observable at 9 pm because the radiant will still be low. It is better to wait till 10 or 11 before going out.

There does seem to be one big problem with tonight’s shower, the weather. Most of the country is under clouds or fog. The visible weather image below was taken at 20:15 UT and is from The National Center for Atmospheric Research (http://www.rap.ucar.edu/weather/satellite/).

Here in Tucson we have 2 storms moving through. The 1st one is here and has produced thick cloud cover. The 2nd is forecast to move through some time tonight and bring some showers with it. I’m hoping for a bit of clear patch between the storms.

Luckily the past 2 nights stayed clearer than predicted. It is obvious that the rate of Geminids have shot up recently. Based on the IMO Real ZHR page, ZHR visual rates were on the order ~40-50 last night. This means last night would have been a fine night for watching meteors. Assuming it is clear, rates for tonight will be 2-3 times greater than last night.

Obs  Date(UT)      Time    TOT SPO ANT GEM HYD MON PSU PUP DAD DLM COM
TUS  2009-12-13   11h 27m  110  13  3   83  4   5   0   0   1   1   0
TUS  2009-12-12   12h 11m   63  14  3   38  4   0   0   1   1   1   1

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
MON - Monocerotids
PSU - Psi Ursae Majorids
PUP - Puppids/Velids
DAD - December Alpha Draconids
DLM - December Leonids Minorids
COM - Coma Berenicids

Highlight on the Geminids

This Sunday evening/Monday morning will bring the peak the Geminids, one of the year’s better meteor showers. It’s usually a toss up as to which is better, the Perseids of August or the Geminids, though lately the Geminids have been routinely out-producing the Perseids. If the sky is clear where you live this Sunday/Monday night will provide one of the few nights of the year when it’s almost guaranteed that you will be able to observe a meteor after about 10-20 minutes of observing.

From a dark, moon-less sky, the Geminids have been known to consistently produce rates of over 100 meteors per hour at their peak. Unlike most showers that can only be observed in the early hours of the morning, the Geminids can be seen in good numbers as early as 10 pm and are great anytime after midnight. The Geminids will appear to radiate from the constellation of Gemini near the bright star Castor.

According to analysis of meteor video data by Sirko Molau, the Geminids are active for almost an entire month between the dates of November 23 and December 21. Though high rates are only possible within a few days of the peak. This year the peak is predicted for the nights of December 13/14.

The International Meteor Organization (IMO) has a “live” graph showing the rate of the Geminids as reported by visual observers around the world.

Most meteor showers are produced by comets with orbits that extend out to the orbit of Jupiter or beyond. The Geminids are different. They are on a very short uncomet-like orbit that extends from a very close 0.14 AU from the Sun to a not so far 2.40 AU.

Orbit diagram of the Geminids and their parent Phaethon. Chart is valid for Dec 13, 2009. Created with the freeware program C2A.

In 1983, the parent body of the Geminids was discovered and surprisingly it looked like an asteroid. Since its discovery, the Geminid parent (3200) Phaethon has not (or has it, more below?) shown any cometary activity. So what is it?

1) Phaethon could be a comet whose original orbit evolved into its current one after many millennia of close approaches with the inner planets. Some models of the formation of the Geminids require the shower particles to be released over many centuries to millennia. This is consistent with the behavior of a comet.

2) Phaethon may be a Main-Belt comet. Main-Belt comets are objects that originate in the outer Asteroid, or Main, Belt. Since they contain a sizable fraction of volatile material (water, carbon monoxide, etc.), they can occasionally exhibit cometary activity. Four of these objects have been observed to display cometary activity in the Main Belt. Since they start on asteroid orbits, it is not too difficult for one of them to find itself on an orbit similar to Phaethon.

3) Phaethon is an asteroid that broke up in the past. There is evidence to suggest that Phaethon is just the largest piece of a past break-up. In fact, two additional asteroids that may once have been a part of Phaethon have been found, (155140) 2005 UD and 1999 YC. According to Peter Jennisken’s book “Meteor Showers and Their Parent Comets”, the Geminids can be explained by the break-up of Phaethon just after perihelion many orbits ago. Since Phaethon gets to within 0.14 AU (14% of the Earth-Sun distance), perhaps it split under the intense solar heat. BTW, this scenario does not rule out Phaethon as a ice-rich Main-Belt comet.

The recent discovery of additional asteroids related to Phaethon points to scenario 3 as the most likely origin of the Geminids. If true, the Geminids were not the result of long-term cometary activity like most meteor showers but were created in a single event when Phaethon split or shed a smaller piece. The Daytime Sextentids and perhaps the very minor Canis Minorids were created by even older break-up events.

Though Phaethon has behaved like an asteroid since discovery there was an event of something weird happening this summer. For a few days this July, the asteroid was visible in near-Sun images taken with the STEREO spacecraft. At the time Phaethon was near perihelion and appeared to be elongated as if it had a short tail. The asteroid also appeared to brighten at the time. Though the details are still sketchy and we await a more rigorous analysis, it is possible Phaethon released some particles for a few days. At the same time the asteroid was in the midst of a relatively dense stream of particles released emanating from the Sun (remember at the time Phaethon was only 0.14 AU from the Sun). Perhaps these particles knocked some fine regolith (science term for asteroid soil) off the surface and this sort of event is a common occurrence for objects with very small perihelia distances.

Meteor Activity Outlook for December 12-18, 2009

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

No matter where you live, the first half of December provides some of the best meteor activity of the year. In the northern hemisphere the sporadic rates are still strong plus you can also count on strong activity from the Geminids, which peak on December 13. There are also several minor radiants that add a few meteors each hour. All of these centers of activity are located high in the sky during the early morning hours this time of year. Unfortunately this year the bright moon spoils the show during the first week of the month. During the second week of December the moon will pass its last quarter phase and will not be such a nuisance .

As seen from the southern hemisphere the sporadic rates are increasing toward a January maximum. Shower rates are also good but the Geminids suffer a bit from the lower elevation seen from southern locations. Still with the warmer weather now occurring south of the equator, December is a great time to view celestial fireworks.

During this period the moon reaches its new phase on Wednesday December 16th. On that date the moon lies near the sun and cannot be seen at night. This weekend the waning crescent moon will rise during the late morning hours but will not cause any interference. The estimated total hourly rates for evening observers this week is near five as seen from the northern hemisphere and three from the southern hemisphere. For morning observers the estimated total hourly rates should be near forty from the northern hemisphere and twenty as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning December 12/13. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

The following showers are expected to be active this week.

Antihelions (ANT)

Now that the activity from particles produced by comet 2P/Encke has ceased encountering the Earth, the Taurid showers for 2009 are over and we resume reporting activity from the Antihelion radiant. This is not a true radiant but rather activity caused by the Earth’s motion through space. As the Earth revolves around the sun it encounters particles orbiting in a pro-grade motion that are approaching their perihelion point. They all appear to be radiating from an area near the opposition point of the sun, hence the name Antihelion. These were once recorded as separate showers throughout the year but it is now suggested to bin them into their category separate from true showers and sporadics. This radiant is a very large oval some thirty degrees wide by fifteen degrees high. Activity from this radiant can appear from more than one constellation. The position listed here is for the center of the radiant which is currently located at 06:16 (094) +23. This position lies in western Gemini near the fourth magnitude star Eta Geminorum. Antihelion activity may also appear from eastern Taurus, northeastern Orion, or southern Auriga. This radiant is best placed near 0100 local standard time (LST) when it lies on the meridian and is highest in the sky. Rates at this time should be ~3 per hour as seen from the northern hemisphere and ~2 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow speed.

Monocerotids (MON)

The Monocerotids (MON) are active from a radiant located at 06:52 (103) +07. This position lies in northwestern Monoceros halfway between the bright stars Betelgeuse (Alpha Orionis) and Procyon (Alpha Canis Minoris). This shower peaked on December 8, so activity is waning. Current rates would most likely average < 1 per hour no matter your location. The Monocerotids are best seen near 0100 LST when the radiant lies highest above the horizon. At 41 km/sec. the Monocerotids produce mostly meteors of medium velocity.

Geminids (GEM)

The Geminids (GEM) are active from a radiant located at 07:33 (113) +32. This position lies in northern Gemini near the fourth magnitude star Rho Geminorum. Although Geminid meteors can be seen all night long, they are best seen near 0200 LST when the radiant lies highest above the horizon. This shower is expected to peak Sunday and Monday December 13/14 when rates can surpass 60 shower members per hour as seen from dark sites. Geminid activity can be seen from the southern hemisphere but at at much reduced rate. As seen from south of the equator, Geminid activity could only be seen for a few hours before and after 0200 LST. At 35 km/sec. the Geminids produce mostly meteors of medium velocity.

Puppids-Velids (PUP)

The Puppid-Velids (PUP) are a vast complex of weak radiants located in the constellations of Puppis and Vela. Visual plots and photographic studies have revealed many radiants in this area during November and December. The combined strength of these radiants can produce a ZHR of 10. Actual hourly rates will be much less unless you happen to be observing from the deep Southern Hemisphere. The center of this activity is currently located at 08:26 (126) -45. This position lies in western Vela, five degrees northeast of the second magnitude star Gamma Velorum. Peak rates occurred near December 7 so current activity is waning. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. Observers located in the Southern Hemisphere have an advantage viewing this shower as the radiant will rise higher into their sky allowing more activity to be seen. At 40 km/sec. the Puppid-Velids produce meteors of medium velocity.

Sigma Hydrids (HYD)

The Sigma Hydrids (HYD) are active from a radiant located at 08:42 (130) +01. This position lies in western Hydra, just below the group of fourth magnitude stars that make up the “head” of the water serpent. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. Current rates would be ~1 per hour no matter your location. At 61 km/sec. the Sigma Hydrids produce mostly swift meteors.

December Leonis Minorids (DLM)

The December Leonis Minorids (DLM) are active from a radiant located at 10:22 (155) +34. This position lies in central Leo Minor, approximately ten degrees north of the third magnitude star Zeta Leonis. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. This shower peaks on December 20th so current rates would be ~1 per hour as seen from the northern hemisphere and < 1 per hour as seen from south of the equator. At 64 km/sec. the December Leonis Minorids produce mostly swift meteors.

Coma Berenicids (COM)

Activity from the Coma Berenicids (COM) has just begun for 2009. The radiant is located at 11:30 (173) +18. This position actually lies in eastern Leo, five degrees northwest of the second magnitude star Denebola (Beta Leonis). These meteors are best seen near 0600 LST when the radiant lies highest above the horizon. This shower peaks on December 16th so current rates would be ~1 per hour no matter your location. At 65 km/sec. the Coma Berenicids produce mostly swift meteors.

December Alpha Draconids (DAD)

Lastly, the December Alpha Draconids (DAD) are active from a radiant located at 14:00 (210) +58. This position actually lies in northeastern Ursa Major, six degrees northeast of the second magnitude double star Mizar (Zeta Ursae Majoris). These meteors are best seen during the last dark hour before dawn, when the radiant lies highest above the horizon in a dark sky. This shower is near the end of its activity period so expected rates would be < 1 no matter your location. At 44 km/sec. the Alpha Draconids produce mostly medium speed meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see ~16 Sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be ~3 per hour. As seen from the mid-southern hemisphere (45S), morning rates would be ~10 per hour as seen from rural observing sites and ~2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week long.

Shower Name                RA     DEC   Vel     Rates
                                        km/s   NH    SH
ANT Antihelions          06h 16m  +23    30     3     2
MON Monocerotids         06h 52m  +07    41    <1    <1
GEM Geminids             07h 33m  +32    35    60    20
PUP Puppids-Velids       08h 26m  -45    40    <1     2
HYD Sigma Hydrids        08h 42m  +01    61     1     1
DLE Dec Leonis Minorids  10h 22m  +34    64     1    <1
COM Coma Berenicids      11h 30m  +18    65     1     1
DAD Dec Alpha Draconids  14h 00m  +58    44    <1    <1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Dec 10/11 Meteors

Lots of bright meteors last night… The Geminids are really ramping up nicely with rates that appear to be twice as high as the previous night. One great thing about the Geminids is that they are visible during most of the night. Unlike most showers which can only be seen during the morning hours, GEMs can be seen within a few hours of sunset.

With the peak scheduled for Sunday night, we are at T-2 nights and counting. Unfortunately for me, the weather forecast still looks horrible for Tucson.

Bob’ notes for the night of Dec 9/10 : “Skies were mostly clear with only thin cirrus during the evening hours. Lower clouds from an approaching front interfered during the morning hours and eventually forced a premature end to the session. The Puppid-Velids and Monocerotids were unusually active tonight.”

Obs  Date(UT)      Time    TOT SPO ANT GEM HYD MON PSU PUP DAD DLM
TUS  2009-12-11   10h 53m   59  20  3   22  4   4   0   1   1   3
SDG  2009-12-11   09h 55m   26  6   1   12  0   4   0   3   0   0

TUS - Camera in Tucson operated by Carl Hergenrother
SDG - Camera in San Diego operated by Bob Lunsford
TotTime - Total amount of time each camera looked for meteors
TOT - Total number of meteors detected
SPO - Sporadics (meteors not affiliated with any particular meteor shower)
ANT - Antihelions
GEM - Geminids
HYD - Sigma Hydrids
MON - Monocerotids
PSU - Psi Ursae Majorids
PUP - Puppids/Velids
DAD - December Alpha Draconids
DLM - December Leonids Minorids

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