THE ESTABLISHED METEOR SHOWERS
P. Jenniskens: Sky&Telescope September 2012
The maps below show the 64 meteor showers that were designated as established during the last IAU General Assembly in 2009 (and in gray some not-yet established showers clearly detected by CAMS), as they show up in the 2007-2009 SonotaCo and 2011 CAMS project data.
January 1-7 (2831 SonotaCo and 381 CAMS)
Meteor showers are named after the nearest star, or constellation of stars, by replacing the declension of the possessive Latin form for "id". The figure above shows the meteor activity in the first week of January. The concentric color pattern reflects the motion of Earth: meteors that collide head-on have a higher speed (red), those that approach Earth sideways are yellow, those that catch up on Earth from behind are blue. The Quadrantids (QUA) originate from short-period asteroidal-looking 2003 EH1, which is now a dormant Jupiter Family Comet (JFC) that broke about 500 years ago. The Quadrantids (QUA) stands 72¼ inclined to the ecliptic plane (dashed line). The alpha Hydrids (AHY) are from an unknown Halley-type comet with a 55¼ inclined orbit. The January Leonids (JLE) are from a rare retrograde (99¼ inclination) JFC source, only recently recognized as a strong shower in radar observations with the Canadian Meteor Orbit Radar (CMOR). The Comae Berenicids (COM) are active in all of December and January. The long activity period points to an unknown Halley-type comet source.
ANTHELION - In blue are the slow meteors from what is called the "anti-helion" source, as in "opposite to the Sun". These are meteors on short-period Jupiter Family Comet (JFC) orbits, taking typically 5-7 years to round the Sun. JFCs originated in the Kuiper Belt. The meteors are seen mostly in the evening and around midnight.
HELION - Some Jupiter Family Comet showers first round the Sun and then approach the Earth from the daytime side. These are called the Helion source, and the showers have the predicate "Daytime" if they approach from less than 32¼ of the Sun. They are sometimes visible in the hour before dawn.
APEX - In red are the fast meteors from the so-called "Apex" source: meteors that collide with Earth nearly head-on. The cameras are particularly sensitive to these fast meteors and see many in the hours before dawn. These are mostly from Long-Period Comets (LPC), orbiting the Sun once every 250 years or more, and Halley-type comets (HTC) which take 20-250 years to round the Sun. These originate in the Oort cloud. Halley-type comets are special because they are in stable orbits and can leave dense meteoroid streams even when the comet itself has moved on.
TOROIDAL - The yellow and green showers are mostly from Jupiter Family and Halley Type comets on inclined or highly eccentric orbits. These tend to not disperse easily and are not as much obscured by sporadic meteors.
January 10-19 (1498 SonotaCo and 450 CAMS)
For ten days centered on January 19, CAMS detected an unusual shower (called a meteor outburst) of Gamma Ursae Minorids (GUM), known from an outburst of bright meteors the year before. GUM are a JFC shower at high 47¼ inclination. SonotaCoÕs discovery of the January Xi Ursae Majorids (XUM) was verified during Jan 17-20. XUM are an unusually short-period (P = 1.8 y) shower of high 67¼ inclination, possibly asteroidal in origin. Several showers from the Bootid - Coronae Borealid cluster were identified in CMOR radar observations. CAMS detected the xi Coronae Borealids (XCB), but not so clearly the lambda Bootids (LBO) or the theta Coronae Borealids (TCB). These are highly inclined Jupiter Family Comet showers.
February 1-6 (370 SonotaCo and 546 CAMS)
On February 4, 2011, CAMS detected a compact cluster of 6 identical orbits of a new shower now called the February eta Draconids (FED). This brief shower was caused by the 1-revolution dust trail of a yet-to-be-discovered long period comet. Such showers occur only on occasion, typically once or twice every 60 years for any given comet, when the cometÕs dust trail wanders briefly in EarthÕs path. The detection of this dust trail was a big deal because it proved the existence of a potentially hazardous comet that could impact the Earth. The alpha Antliids (AAN) are from a low-q = 0.14 AU, high inclination (~50¼) Jupiter Family comet source that has not yet been identified. The other established shower in February, the southern hemisphere alpha Centaurids (ACE), are not visible from California. That shower is known from annual activity and occasional meteor outbursts.
March 1-31 (1863 SonotaCo and 294 CAMS)
In March, there are no established showers yet. This is the one month in the year when California weather is consistently cloudy. SonotaCo data (above) shows activity from the short period eta Virginids (EVI) in the middle of the month, a Jupiter Family comet shower not yet in the list of established showers.
April 8-25 (802 SonotaCo and 256 CAMS)
Around the 22nd of April peaks the Lyrid (LYR) shower from an unusual long-period comet C/1861 G1 Thatcher. The comet orbit is short enough (about 415 years) to build up a dense stream. The 1-revolution trail causes intense outbursts about every 60 years. In the days following the Lyrids, comet HalleyÕs Eta Aquariids (EAQ) first show up in the early morning. The kappa Serpentids (KSE) are active for a few days around April 10, a high 68¼ inclined JFC shower. Not shown are the pi Puppids (PPU), a southern hemisphere shower known for periodic meteor outbursts that originate from weakly active JFC 26P/Grigg-Skjellerup, and the Daytime April Piscids (APS).
April 26 Ð May 14 (1804 SonotaCo and 1861 CAMS)
Around May 10 peak the eta Lyrids (ELY) from big, but weakly active, long-period comet C/1983 H1 IRAS-Araki-Alcock. In late April and early May, a Jupiter-family comet shower with a relatively high inclination creates the April rho Cygnids (ARC), a shower discovered in the CMOR data and confirmed by CAMS. In this time of year, the blue anthelion showers are strong, but the streams are dispersed and only discriminated in the day-to-day plots. So far, SonotaCo and CAMS picked up just one meteor each of the Northern Daytime omega Cetids (NOC), a low-q high inclination Jupiter Family comet shower. Radar also recognize the Southern Daytime omega Cetids (OCE) and the Southern Daytime May Arietids (SMA).
On occasion, Earth will encounter dust from comet 73P/Schwassmann-Wachmann in late May and early June, creating a shower called the theta Herculids (THE). Around June 7, the Daytime Arietids (ARI) are detected in the CAMS data in the hour before dawn. We were able to demonstrate that the meteoroids had the same semi-major axis as the Marsden group of Sungrazers, and we suspect that both comet family and meteoroid stream were created at the same time from a comet disruption. Radar detect the Daytime zeta Perseids (ZPE) and Daytime beta Taurids (BTA), which are the twin showers of the Northern and Southern Taurids in November. Radar also detect the Daytime lambda Taurids (DLT).
June 22 Ð July 6 (467 SonotaCo and 1683 CAMS)
Late June is best known for occasional outbursts of the June Bootid shower (JBO) from weakly active JFC comet 7P/Pons-Winnecke. No such outburst occurred in recent years. The Corvids (COR) were only seen by Cuno Hoffmeister, who noticed many slow meteors on several days around June 26, 1937, while observing from the southern hemisphere. The annual Northern June Aquilids (NZC) is a strong shower starting in June, but lasting until the end of July. It has a counter part, the Southern June Aquilids (SZC), which is detected for a shorter period in early July. Both JFC showers have a short perihelion distance, but relatively high inclination. These are not part of the Machholz Complex of streams that include the Daytime Arietids. The epsilon Perseids (EPR) are mostly a daytime shower, but a few meteors were detected. CAMS now also confirms strong activity from apex showers phi Piscids (PPS), detected by CMOR, and c Andromedids (CAN), first detected by single-station video observations collected by the International Meteor Organization.
A few showers in the current list of established showers were not detected, all active around July 8-9: the alpha Lacertids (ALA), the epsilon Pegasids (EPG), the beta Equuleids (BEQ), and the psi Cassiopeiids. This could change when more meteors are observed. Radar observations also recognize the Daytime xi Orionids (XRI), which we cannot observe.
July 22 Ð August 2 (1461 SonotaCo and 2414 CAMS)
The Northern June Aquilids persist until the first day of August. In the last week of July, a new shower emerges at lower inclination (and Declination), the Northern delta Aquariids (NDA), part of the Machholz complex. The Southern Delta Aquariids (SDA) are much stronger and have their maximum around July 29. Only recently, Machholz group sungrazer 2008 Y12 was recognized to be in an orbit similar to this stream. Further west originate the slower alpha Capricornids (CAP) from mostly dormant JFC comet 169P/NEAT, which broke about 5000 years ago. This shower is expected to increase in intensity in the future and peak as a major shower around 2375 AD. CAMS was able to verify the July gamma Draconids (GDR), a long-period comet shower active around July 28.
August 6-16 (6135 SonotaCo and 3968 CAMS)
The Perseids from Halley-type comet 109P/Swift-Tuttle are first detected around July 12 and last through August 27. Another such long-duration shower, of possibly Halley-type origin, the eta Eridanids (ERI) appear south of the ecliptic plane around July 19 and last until August 21. The proposed parent, comet C/1852 K1 Charcornac, was not well observed and has a somewhat different perihelion distance.
The kappa Cygnids (KCY) were not detected in the CAMS data from 2011, but do show up strong in the Sonotaco data. This is a periodic shower from dormant Jupiter family comet 2008 ED69. The stream produces meteors mostly at Venus. The nearby August Draconids (AUD) are a brief JFC shower around August 14 with the same ~33¼ inclination as the kappa Cygnids and may be related. This shower is now confirmed. The Piscis Austrinids (PAU) are active in early August from a 56¼ inclined JFC source with an orbit that stretches well beyond Jupiter. Not so obvious in the data are the Northern iota Aquariids (NIA), nomally peaking around August 20, and the Southern iota Aquariids (SIA), nomally peaking on August 4. The anthelion source does seem split in two. Finally, the southern hemisphere beta Hydrusids (BHY) are only known from a spectacular outburst on August 17, 1985.
August 31 Ð September 12 (1774 SonotaCo and 1866 CAMS)
California was showerd by Aurigids (AUR) from the 1-revolution dust trail of long-period comet C/1911 N1 Kiess on September 1, 2007. A weak annual shower is detected in CAMS data. From about September 9 to 12 is the peak of the September epsilon Perseids (SPE), from an unknown long-period comet. The southern apex source has a diffuse shower called the nu Eridanids (NUE), first detected in the SonotaCo data and verified by CAMS. This is a retrograde 140¼ inclined shower from a Halley-type comet. Early September sees emerging what is often called the Taurid complex, with two branches: the Northern Taurids (NTA) and the Southern Taurids (STA). A complicated pattern of brief showers start in the first week of September. CAMS data suggests that individual names are warranted.
September 20 Ð October 10 (2341 SonotaCo and 3288 CAMS)
The Daytime Sextantids is associated with asteroid 2005 UD, and with the Geminids/3200 Phaethon part of the Phaethon family, the only established association of meteor showers with asteroids. The weaker Daytime kappa Leonids (KLE) were not detected. Early October is known for a number of irregular showers. The October Capricornids (OCC) derive from mostly dormant comet D/1978 R1 Haneda-Campos, which was recently trapped in the 2:1 mean-motion resonance that can trap dust as well. A meteor outburst was observed in 1978. On October 8, 2011, an intense outburst of October Draconids (DRA) from comet 21P/Giacobini-Zinner was observed from Europe. Two CAMS computers were operated from Kuehlungsborn, in Germany, providing the data shown. The radiant of the October Camelopardalids (OCT) was only recently determined by Finnish observer Jarmo Moilanen from video observations of an outburst of meteors on October 5, 2005.
October 18-29 (7683 SonotaCo)
At the time of the peak of the Orionid (ORI) shower from comet 1P/Halley, on October 22, the Leonids Minorids (LMI) from comet C/1739 K1 (Zanotti) are active, as well as a diffuse epsilon Geminids (EGE) from an unknown source. This shower was previously known from sparse photographic data and is now confirmed. At this time of the year, the Southern Taurids are more active than the Northern.
November 1-10 (2474 SonotaCo and 2140 CAMS)
In the first week of November, part of the Northern Taurids (NTA) are associated with dormant comet 2004 TG10. Other parent bodies are suspected for other parts of the Taurid complex. The Andromedids (AND) are much slower meteors that originate from now "D" Jupiter Family Comet 3D/Biela. The chi Taurids (CTA) and the theta Aurigids (THA) showers, confirmed by CAMS, have radiants close together, but different entry speeds. These are very different streams. THA is a highly eccentric, low perihelion distance, JFC shower. CTA are a 17¼ inclined prograde Halley-type stream. Further south are the omicron Eridanids (OER), from a relatively high inclination JFC with 8-year period. The Orionids (ORI) are still active in early November, while the Leonids (LEO) from Halley-type comet 55P/Tempel-Tuttle are just emerging. Finally, on November 5, 2009, SonotaCo detected an outburst of a new long-period comet shower north of the Leonids, now called the Kappa Ursae Majorids (KUM). CAMS measured one KUM orbit in 2011.
December 1-8 (4250 SonotaCo and 3240 CAMS)
December 3-6, CAMS detected yet another meteor outburst with a radiant in Cassiopeia, this time from a Jupiter Family Comet, now called the December phi Cassiopeiids (DPC). A number of low-q showers show up in this compilation of CAMS and SonotaCo data. On November 11, the Halley-type November Orionids (NOO) first emerge and last until the peak of the Geminids in mid December, caused by an unknown Halley-type comet. The December Monocerotids (MON) show up on December 1 and lasts until the peak of the Ursids. This, too, is a Halley-type comet, probably comet C/1917 F1 (Mellish), although the orbital period of this comet is uncertain. The Geminids (GEM) are a highly eccentric high-inclination short-period shower, which originated from an asteroid, 3200 Phaethon. A number of other high inclination near-Earth asteroids are known that have similar gray reflection spectra, forming a trail of breadcrumbs that lead to asteroid 2 Pallas and its associated asteroid family. The Leonids continue to be detected in early December. The December Comae Berenicids (COM) emerge on December 2nd, but continue until the end of January. CAMS detected a weak annual alpha Monocerotid (AMO) shower around November 22, from an unknown long-period comet. The 1-revolution dust trail of which caused the predicted 1995 outburst. At the same time, another shower emerges just north of it, called the sigma Hydrusids (HYD). This Halley-type shower swells to a major shower on December 6. No parent body is known. The southern hemisphere Phoenicids (PHO) are periodic, and originate from D/1819 W1 Blanpain. A remnant of the comet was discovered recently called 2003 WY25. It was small, but still weakly active at perihelion. The Northern Taurids and Southern Taurids continue into December. Just west of the Southern Tuarids are the Southern chi Orionids (ORS), a shower that is now confirmed. The 74¼ inclined Halley-type December kappa Draconids (KDR) were first recognized in SonotaCo data and later also detected in the CMOR radar observations. The December alpha Draconids (DAD) are a 72¼ short-period JFC stream. The 170¼ retrograde long-period December chi Virginids (XVI) are now also verified. The 119¼ inclined Halley-type psi Ursae Majorids (PSU) were detected by CMOR and are now confirmed.
December 18-25 (2805 SonotaCo)
The Ursids (URS) originate from Halley-type comet 8P/Tuttle. The shower has occasional outbursts. This time of year, in late December, the December Comae Berenicids (COM) peak, but the shower is active throughout December and January. The 107¼ inclined long-period alpha Lyncids (ALY) are confirmed by CAMS. Finally, radar observations find two nearby daytime radiants with slightly different speed in Serpens: the omega Serpentids (OSE) and the sigma Serpentids (SSE). A few meteors of these showers were detected by CAMS in early morning hours.