Radiation astronomy/Showers

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The Aurigid meteor shower is observed by a group of astronomers on a NASA mission at 47,000 feet. Credit: Jeremie Vaubaillon, Caltech, NASA.{{free media}}

Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated. All of the orbits passed through the asteroid belt.[1]

"Named meteor showers recur at approximately the same dates each year. They appear to "radiate" from a certain point in the sky (the radiant) and vary in the speed, frequency and brightness of the meteors."[2]

As of November 2018, there are 112 established meteor showers.[3]

Radiants[edit]

Image shows a meteor shower, with the radiant marked by o. Credit: Anton~commonswiki.

The radiant, apparent radiant, or radiant point of a meteor shower is the celestial sphere point in the sky from the point of view of a terrestrial observer that the paths of meteors appear to originate.[4]

Nomenclature Rules for Meteor Showers[edit]

"The following nomenclature rules are adopted for meteor showers, keeping in mind that it is not always known precisely during discovery when is the peak of a meteor shower and what is the position of the radiant at that time. For known showers, the Working Group may choose a traditionally accepted name (e.g., alpha-Monocerotids) over the more correct name after a radiant has been established (which would have suggested the name of delta-Canis Minorids)."[5]

"The general rule is that a meteor shower (and a meteoroid stream) should be named after the constellation that contains the nearest star to the radiant point, using the possessive Latin form. The possessive Latin name for the constellations end in one of seven declensions:"[5]

  • ae (e.g., Lyrae),
  • is (e.g., Leonis),
  • i (e.g., Ophiuchi),
  • us (e.g.,Doradus),
  • ei (e.g., Equulei),
  • ium (e.g., Piscium), or
  • orum (e.g., Geminorum).

"Custom is to replace the final suffix for '-id', or plural '-ids'. Meteors from Aquarius (Aquarii) are Aquariids, not Aquarids. An exception is made for meteors from the constellation of Hydrus,which will be called 'Hydrusids', in order not to confuse with meteors from the constellation of Hydra."[5]

"When the constellation name has two parts, only the second declension is to be replaced by 'id'. Hence, meteors from Canes Venatici (Canum Venaticorum) would be 'Canum Venaticids'. When two constellations are grouped together, a bracket is used and both constellation names will have 'id'. Hence, Puppids-Velids. As a guideline, the order of the constellations should be in the same sequence as the radiant daily motion."[5]

"If a higher precision is needed, then the shower is named after the nearest (if in doubt: brightest) star with a Greek letter assigned, as first introduced in the Uranometria atlas by Johann Bayer (1603), or one with a later introduced Roman letter. If in doubt, the radiant position at the time of the peak of the shower (in the year of discovery) should be taken. Hence, the meteors of comet IRAS-Araki-Alcock would be named 'eta-Lyrids'."[5]

"In that case, if a meteor shower radiant is near the border of a constellation and the nearest such star is in the neighboring constellation, then the shower is named after that star."[5]

"Following existing custom, one may add the name of the month to distinguish among showers from the same constellation. In this case, one could call the shower from comet IRAS-Araki-Alcock the 'May Lyrids', in order to differentiate from the more familiar 'April Lyrids'."[5]

"For daytime showers, it is custom to add 'Daytime', hence the name for the 'Daytime Arietids' in June as opposed to the Arietids in October. As a guideline, the stream radiant should be less than 32 degs from the Sun to be called a daytime shower. This ensures that no where is the radiant more than 20 degs above the horizon at the start of local Nautical twilight."[5]

"South and North refer to 'branches' of a shower south and north of the ecliptic plane (stricktly the orbital plane of Jupiter), resulting from meteoroids of the same (original) parent body. Because they have nearly the same longitude of perihelion at a given solar longitude (the argument of perihelion and longitude of ascending node differing by 180 degrees between South and North), the two branches are active over about the same time period."[5]

"If the meteoroid stream is encountered at the other node, it is customary to speak of 'twin showers'. The Orionids and eta-Aquariids are twin showers, even though each represent dust deposited at different times and are now in quite different orbits. As a matter of custom, twin showers and the north and south branches of a stream carry different names. Meteor showers are not to be named after their parent bodies (e.g., Giacobinids, IRAS-Araki-Alcockids). The names of comets tend not to be Latin, making the naming not unique. Also, comet names can change when they get lost and are recovered."[5]

"The Working Group for Meteor Shower Nomenclature will choose among possible alternative proposed names for newly identified meteor showers, in order to establish a unique name for each meteor shower (e.g., eta-Lyrids, not May Lyrids)."[5]

Potential meteor shower nomenclatures[edit]

  1. Andromeda Andromedids
  2. Anser Anserids
  3. Antinous Antinousids
  4. Antlia Antliids
  5. Apus Apodids
  6. Aquarius Aquariids
  7. Aquila Aquilids
  8. Ara Arids
  9. Argo Navis Argus Navids
  10. Aries Arietids
  11. Officina Typographica Officinae Typographicids
  12. Auriga Aurigids
  13. Globus Aerostaticus Globus Aerostaticids
  14. Boötes Boötids
  15. Caelum Caelids
  16. Camelopardalis Camelopardalids
  17. Cancer Cancrids
  18. Canes Venatici Canum Venaticids
  19. Canis Major Canis Majorids
  20. Canis Minor Canis Minorids
  21. Capricornus Capricornids
  22. Caput Medusae Caput Medusids
  23. Carina Carinids
  24. Cassiopeia Cassiopeiids
  25. Centaurus Centaurids
  26. Cepheus Cepheids
  27. Cerberus Cerberids
  28. Cetus Cetids
  29. Chamaeleon Chamaeleontids
  30. Circinus Circinids
  31. Columba Columbids
  32. Coma Berenices Comae Berenicids
  33. Corona Australis Coronae Australids
  34. Corona Borealis Coronae Borealids
  35. Corvus Corvids
  36. Crater Craterids
  37. Crux Crucids
  38. Custos Messium Custus Messiids
  39. Cygnus Cygnids
  40. Delphinus Delphinids
  41. Dong’ou Dong’ouids
  42. Dorado Doradids
  43. Draco Draconids
  44. Equuleus Equuleids
  45. Eridanus Eridanids
  46. Felis Felids
  47. Fornax Fornacids
  48. Gemini Geminids
  49. Gloria Frederici Gloriae Fredericids
  50. Grus Gruids
  51. Hercules Herculids
  52. Horologium Horologiids
  53. Hut Hutids
  54. Hydra Hydrids
  55. Hydrus Hydrusids
  56. Indus Indids
  57. Lacerta Lacertids
  58. Legs Legsids
  59. Leo Leonids
  60. Leo Minor Leonis Minorids
  61. Lepus Leporids
  62. Libra Librids
  63. Lupus Lupids
  64. Lynx Lyncids
  65. Lyra Lyrids
  66. Machina Electrica Machinae Electricids
  67. Mensa Mensids
  68. Microscopium Microscopiids
  69. Monoceros Monocerotids
  70. Mons Mænalus Mons Mænalids
  71. Musca Muscids
  72. Noctua Noctuids
  73. Norma Normids
  74. Octans Octantids
  75. Ophiuchus Ophiuchids
  76. Orion Orionids
  77. Pavo Pavonids
  78. Pegasus Pegasids
  79. Perseus Perseids
  80. Phoenix Phoenicids
  81. Pictor Pictorids
  82. Pisces Piscids
  83. Piscis Australis Piscis Austrinids
  84. Psalterium Georgii Psalterii Georgiids
  85. Puppis Puppids
  86. Pyxis Pyxidids
  87. Quadrans Muralis Quadrantids
  88. Rangifer Rangiferids
  89. Reticulum Reticulids
  90. Sagitta Sagittids
  91. Sagittarius Sagittariids
  92. Sarvvis Sarvvids
  93. Scorpius Scorpiids
  94. Sculptor Sculptorids
  95. Scutum Scutids
  96. Serpens Caput Serpentids
  97. Serpens Cauda Serpentids
  98. Serpentarius Serpentariids
  99. Sextans Sextantids
  100. Tarandus Tarandids
  101. Taurus Taurids
  102. Telescopium Telescopiids
  103. Telescopium Hershelii Telescopii Hersheliids
  104. Tianmiao Tianmiaids
  105. Triangulum Triangulids
  106. Triangulum Australe Trianguli Australids
  107. Tucana Tucanids
  108. Taiwei Taiweids
  109. Ursa Major Ursae Majorids
  110. Ursa Minor Ursae Minorids
  111. Ursus Ursids
  112. Vela Velorids
  113. Virgo Virginids
  114. Volans Volantids
  115. Vulpecula Vulpeculids

Andromedids[edit]

The Andromedids of 27 November 1872 is a product of the breakup of Biela's Comet several decades previously. Credit: Amedee Guillemin.

The Andromedids meteor shower is associated with Biela's Comet, the showers occurring as Earth passes through old streams left by the comet's tail. The comet was observed to have broken up by 1846; further drift of the pieces by 1852 suggested the moment of breakup was in either 1842 or early 1843, when the comet was near Jupiter.[6][7] The breakup led to particularly spectacular showers in subsequent cycles (particularly in 1872 and 1885).[8][9]

Radiant of the Andromedids in December 2013 is near γ Cassiopeiae (near the middle of the W).[10] Right ascension = 01h 36m[11] and Declination = +37°[11]

Occurs during September 25 – December 6,[8] date of peak is November 9[11], Velocity = 19 km/s[11] and its Zenithal hourly rate = 3[11].

The first known sighting of the Andromedids was December 6, 1741, over St Petersburg, Russia.[9]

The 1872 shower consisted mainly of faint (5th to 6th magnitude) meteors with "broad and smoke-like" trains and a predominantly orange or reddish colouration.[12] The same shower produced at least 58,600 visible meteors between 5.50 and 10.30 pm, observed in England and that the meteors were much slower than the Leonids], with noises "like very distant gun-shots" several times to the north-west.[13] In Burma, the 1885 shower was perceived as a fateful omen and was indeed followed swiftly by the collapse of the Konbaung dynasty and the conquest by Britain.[14]

The November 27, 1885, shower was the occasion of the first known photograph of a meteor, taken by Austro-Hungarian astronomer, Ladislaus Weinek, who caught a 7 mm-long trail on a plate at his Prague observing station.[15]

Since the 19th century the Andromedids have faded so substantially that they are no longer generally visible to the naked eye, though some activity is still observable each year in mid-November given suitable detection equipment.[9] In recent years, peak activity had been less than three meteors per hour, around November 9[11] to 14.[8] Andromedid activity of November comes from the newest streams, while that of early December comes from the oldest.[8]

On December 4, 2011, six Canadian radar stations detected 50 meteors in an hour. The activity was likely from the 1649 stream.[16] On December 8, 2013, Meteor specialist Peter Brown reported that the Canadian Meteor Orbit Radar had recorded an outburst from the Andromedid meteors in the past 24 hours.[10] Scientists postulate a somewhat weaker return in 2018, but a yield of up to 200 meteors an hour in 2023.[16][17] Canadian Meteor Orbit Radar (CMOR) data also detected a spike of 30 meteors per hour on November 27, 2008.[16]

During the 2012 shower an inconspicuous maximum occurred on November 9.[11]

Anthelion[edit]

"The center of the large Anthelion (ANT) radiant is currently located at 19:24 (291) -22. This position lies in eastern Sagittarius, 1 degree east of the bright planet Saturn. This area of the sky is best placed near 02:00 LDST when it lies highest above the southern horizon. Due to the large size of this radiant, anthelion activity may also appear from Scutum as well as Sagittarius. Rates at this time should be near 2 per hour as seen from mid-northern latitudes (45 N) and 3 per hour as seen from the southern tropics (S 25). With an entry velocity of 30 km/sec., the average anthelion meteor would be of slow velocity."[18]

RA 18:24 (291 RA in degrees) Declination -22, entry velocity 30 km/s, hourly rate = 2-3, Class 11.[18]

Alpha Antliids[edit]

"From the IMO working list of meteor showers, 𝛅-Leonids and meteors from the Antihelion Source were detected. For the first time, 𝛂-Antliids were detected in the optical domain."[19]

A "possible weak shower from February 2 to 7 (solar longitude 313-318°), [is] based on just 66 shower members. On February 4, the average radiant lies at 𝛂 = 162°, 𝛅 = -14° [...]. The mean meteor shower velocity is 45 km/s."[19]

The "IAU Working list of meteor showers lists the 𝛂-Antliids (AAN) shower (No. 110) with quite similar characteristics (𝛂 = 140°, 𝛅 = -10°, vini = 43 km/s) on February 2. It appears that the shower was first detected by the Advanced Meteor Orbit Radar (AMOR) at 𝛂 = 162°, 𝛅 = -13°, vini = 43 km/s (Galligan & Baggaley, 2002). The shower was also found by the Canadian Meteor Orbit Radar (CMOR) (Brown et al., 2008). According to their latest analysis, 𝛂-Antliids are active between solar longitude 308 and 321 degrees. On February 4 the shower lies at 𝛂 = 162°, 𝛅 = -12° [...]. Also the meteor shower velocity (44 km/s) matches well to the video data. Thus the existence of the 𝛂-Antliids is now also proved in the optical domain. [...] The activity profile [...] shows that the ZHR will hardly exceed 1 in the full activity interval."[19]

Eta Aquariids[edit]

Animation is of 1P/Halley orbit - 1986 apparition.   1P/Halley   Earth   Sun. Credit: Phoenix7777.

The current orbit of Halley's Comet does not pass close enough to the Earth to be a source of meteoric activity.[20]

The shower is best viewed from the equator to 30 degrees south latitude.[20]

The meteoroids are from very old ejection from the parent 1P/Halley and are trapped probably in resonances to Jupiter's orbit (similar to the Orionids observed between 2007 and 2010).[21]

The peak ZHR reached 135 ± 16.[22] Updated information on the expected time and rates of the shower is provided through the annual IMO Meteor Shower Calendar.[21]

"At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."[23]

Southern Delta Aquariids[edit]

Meteors radiating from near the star Delta Aquarii (declension "-i") are called the Delta Aquariids.

Parent body = 96P/Machholz[24]

Zenithal hourly rate = 16[24]

The Southern Delta Aquariids[25] are a meteor shower visible from mid July to mid August each year with peak activity on 28 or 29 July. The shower originated from the breakup of what are now the Marsden and Kracht Sungrazing comets.[24]

Both accurate velocity and orbit of the δ Aquariids was determined with a "more selective beamed aerial" (echo radio) to identify probable member meteors and plotted an accurate orbital plane, as a broad "system of orbits" that are probably "connected and produced by one extended stream."[26]

Radiant: 22:40 -16.4°, Velocity: 26 miles/sec (medium - 41km/sec).[27]

Arietids[edit]

The Arietids are a strong meteor shower that lasts from May 22 to July 2 each year, and peaks on June 7. The Arietids, along with the Zeta Perseids, are the most intense daylight meteor showers of the year.[28] The source of the shower is unknown, but scientists suspect that they come from the asteroid 1566 Icarus,[28][29] although the orbit also corresponds similarly to 96P/Machholz.[30]

First discovered at Jodrell Bank Observatory in England during the summer of 1947, the showers are caused when the Earth passes through a dense portion of two interplanetary meteoroid streams, producing an average of 60 shooting stars each hour, that originate in the sky from the constellation Aries and the constellation Perseus.[8] However, because both constellations are so close to the Sun when these showers reach their peak, the showers are difficult to view with the naked eye.[28] Some of the early meteors are visible in the very early hours of the morning, usually an hour before dawn.[31] The meteors strike Earth's atmosphere at speeds around 39 km/s.[28]

By June 22 the radiant has migrated to the constellation Taurus (3h 51m +27) which is the same constellation that the Beta Taurids peak on June 28.[32]

Aurigids[edit]

Aurigids is a meteor shower occurring primarily within September.[33]

The comet Kiess (C/1911 N1) is the source of the material that causes the meteors, with an orbital period as approximately 1800 to 2000 years, and showers observed in the years 1935, '86, '94 and 2007 .[34][35]

The Alpha were discovered by C. Hoffmeister and A. Teichgraeber, during the night of 31 August 1935.[8][36]

June Bootids[edit]

The meteor shower Bootids during the maximum in 2016. Credit: HemelWaarnemen.{{free media}}

"The June Bootid meteor shower is active each year from June 26th until July 2nd. It peaks on June 27th. Normally the shower is very weak, but occasional outbursts produce a hundred or more meteors per hour."[37]

"The shower's radiant lies in the constellation Bootes (right ascension 14h 56m, declination 48°)."[37]

"The source of the June Bootids is periodic comet 7P/Pons-Winnecke."[37]

"June Bootid meteoroids hit Earth's atmosphere with a velocity of 18 km/s (40,000 mph).They are considered slow-moving meteors."[37]

"On June 27th, 1998, northern sky watchers were surprised when meteors suddenly began to stream out of the constellation Bootes. Observers saw as many as 100 meteors per hour during the 7-hour-long outburst. It wasn't the first time: similar outbursts from Bootes had been recorded in 1916, 1921 and 1927. Astronomers call these unpredictable meteors the June Bootids."[37]

Delta Cancrids[edit]

The Delta Cancrids is a medium strength meteor shower lasting from December 14 to February 14,[38] the main shower from January 1 to January 24.[39][40] The radiant is located in the constellation of Cancer, near Delta Cancri. It peaks on January 17 each year, with only four meteors per hour.[39][40] It was first discovered in 1872, but the first solid evidence of this phenomenon came in 1971.[38] The source of this meteor shower is unknown, it has been suggested that it is similar to the orbit of asteroid 2001 YB5.[41]

Alpha Capricornids[edit]

Alpha Capricornids is a meteor shower that takes place as early as 15 July and continues until around 10 August.[42]

The parent body is asteroid 2002 EX12 [169P/NEAT], which in the return of 2005 was found weakly active near perihelion.[43]

"Minor planet 2002 EX12 ... is identified as the parent body of the alpha Capricornid shower, based on a good agreement in the calculated and observed direction and speed of the approaching meteoroids for ejecta 4500-5000 years ago....The bulk of this matter still passes inside Earth's orbit, but will cross Earth's orbit 300 years from now. As a result, the alpha Capricornids are expected to become a major annual shower in 2220-2420 A.D., stronger than any current annual shower"[43]

The meteor shower was created about 3,500 to 5,000 years ago, when about half of the parent body disintegrated and fell into dust.[43]

The Alpha Capricornids are expected to become a major annual storm in 2220–2420 A.D., one that will be "stronger than any current annual shower."[43]

Alpha Centaurids[edit]

"The Alpha Centaurids are a meteor shower in the constellation Centaurus, peaking in early February each year. The average magnitude is around 2.5, with a peak of about three meteors an hour."[44] "They have been observed since 1969".[44]

"The Alpha Centaurids emanate from α=216°, δ=-60° [...] The Alpha Centaurids have maximum hourly rates of 3 [...] The Alpha Centaurids have an average magnitude of 2.45 [...] During 1979, members of the Western Australia Meteor Section (WAMS) managed to observe the "Alpha Centaurids" during February 2-18. At maximum on February 7, the radiant is at α=216°, δ=-59°. [...] First of all, the Alpha Centaurids are apparently a consistent shower, with Buhagiar assigning an hourly rate of 3, and WAMS observers detecting high rates of 2 (ZHR calculated as 8.56+/-4.94) in 1979. [...] The Alpha Centaurids may have been detected by radar at Adelaide Observatory during 1969. G. Gartrell and W. G. Elford operated the radar system during February 10-17. Two meteors were noted from a radiant of α=223°, δ=-61°, with the date of nodal passage being determined as February 15. Assuming these meteors are members of the Alpha Centaurids, then this stream orbit has an inclination near 105°, and a semimajor axis near 2.5 AU. This identification would also indicate that the radiant's daily motion is very close to +1° in α. The movement in δ can not be determined from the available observations."[45]

Beta Centaurids[edit]

The "Beta Centaurids have a radiant of α=208°, δ=-58°. [...] the Beta Centaurids can reach hourly rates as high as 14. [...] the Beta Centaurids are probably about 1.6. [...] M. Buhagiar (Western Australia),[...] obtained observations of both Centaurid radiants during 1969-1980. In his "Southern Hemisphere Meteor Stream List" of 1980, Buhagiar listed two radiants which reached maximum on February 7. "Radiant 290" was active during February 6-8, from α=206°, δ=-57°, while "radiant 299" was active during February 5-9, from α=214°, δ=-64°. Both radiants were referred to as "Beta Centaurids." [...] During 1980, the same group observed members of the "Alpha Centaurids" during February 2-24. [...] the 1980 radiant is the Beta Centaurids. [...] The Beta Centaurids are apparently variable in activity, according to Buhagiar, with his 1969-1980 observations revealing high rates of 10 meteors per hour. WAMS observers obtained maximum rates of 11-14 per hour (ZHR calculated as 28.48+/-4.88) during a one-hour interval on 1980 February 8/9. [...] during 1980, 169 Beta Centaurids revealed an average magnitude of 1.6 (the latter number is an approximation by the Author based on a table published in the October 1980 issue of Meteor News)."[45]

Kappa Cygnids[edit]

Kappa Cygnids, abbreviated KCG, is a minor meteor shower that takes place in August along with the larger Perseids meteor shower.[46]

The Kappa Cygnids in 2009 were Active between August 3-August 25 August, with Peak of shower at August 17, and ZHR = 3 km/s.[47]

Draconids[edit]

Composite image of Draconid meteors taken from Petnica Meteor Group (http://www.meteori.rs) video camera stationed at Institute of Physics, Belgrade. Credit: Petnica Meteor Group.{{free media}}

The October Draconids, in the past also unofficially known as the Giacobinids, are a meteor shower whose parent body is the periodic comet 21P/Giacobini-Zinner.[8] They are named after the constellation Draco, where they seemingly come from. Almost all meteors which fall towards Earth ablate long before reaching its surface. The Draconids are best viewed after sunset in an area with a clear dark sky. RA 17.467h[8] and Declination = +54°[8]. Velocity = 20 km/s.[48]

The 1933[49][50][51] and 1946[49] Draconids had Zenithal Hourly Rates of thousands of meteors visible per hour, among the most impressive meteor storms of the 20th century. Rare outbursts in activity can occur when the Earth travels through a denser part of the cometary debris stream; for example, in 1998, rates suddenly spiked[52][53] and spiked again (less spectacularly) in 2005.[54] A Draconid meteor outburst occurred[55] as expected[56][57][58] on 2011 October 8, though a waxing gibbous Moon reduced the number of meteors observed visually.

"Observers in the UK and Northern Europe are ideally placed to see the peak of the Draconids. Unfortunately the peak occurs in the day time for North America. There will also be a bright Moon which may drown out many but the brightest meteors, but if predictions are correct, you will still see many. You may see Draconid meteors on the 7th an the 9th also, so it is worth going out and checking the skies."[56]

During the 2012 shower radar observations detected up to 1000 meteors per hour. The 2012 outburst may have been caused by the narrow trail of dust and debris left behind by the parent comet in 1959.[59]

Geminids[edit]

A Geminid meteor in 2007, seen from San Francisco. Credit: Brocken Inaglory.
Geminid meteors clearly show the position of the radiant. Credit: Berkó Ernő.

The Geminids are a prolific meteor shower caused by the object 3200 Phaethon,[60] which is thought to be a Palladian asteroid[61] with a "rock comet" orbit.[62]

Leonids[edit]

The photograph shows the meteor, afterglow, and wake as distinct components of a meteor during the peak of the 2009 Leonid Meteor Shower. Credit: Navicore.
This photograph shows the Leonids as many begin contacting the Earth's atmosphere. Credit: NASA.

"The Leonid meteor shower peaked early Saturday (Nov. 17 [2012]), and some night sky watchers caught a great view. The Leonids are a yearly meteor display of shooting stars that appear to radiate out of the constellation Leo. They are created when Earth crosses the path of debris from the comet Tempel-Tuttle, which swings through the inner solar system every 33 years."[63]

Leonis Minorids[edit]

Parent body: C/1739 K1 (Zanotti).[64]

June Librids[edit]

The "June Librid shower, which had not been observed since 1937, was active in 1992."[65]

The "Librid meteor shower (RA = 227.2°, Dec = -28.3°) [...] was optically observed by Cuno Hoffmeister on 1937 June 8-9, but, to the knowledge of the authors, not since (Hoffmeister 1948; Cook 1973; M. Gyssens & P. Roggemans, personal communication, 1992)."[65]

An "initial set of data collected on 1992 June 6-9 [...] indicate that the June Librid shower was active in 1992, having only previously been observed (visually) in 1937."[65]

Only "about 10 June Librids were detected in total."[65]

"The observations by Link (1975) had shown that there was a certain correlation between enhanced twilight scattering above 70 km and the occurrences of Orionid, Geminid and Librid meteor showers."[66]

Lyrids[edit]

Radiant point of the April Lyrid meteor shower is shown, active each year around April 22. Credit: NASA/Don Pettit.
On the night of April 21, the 2012 Lyrid meteor shower peaked in the skies over Earth. While NASA allsky cameras were looking up at the night skies, astronaut Don Pettit aboard the International Space Station trained his video camera on Earth below. Credit: NASA/Don Pettit.{{free media}}

The April Lyrids (LYR, IAU shower number 6)[67] is a meteor shower lasting from April 16 to April 26[68]

The source of the meteor shower is particles of dust shed by the long-period Comet C/1861 G1 Thatcher.[24]

The Lyrids have been observed and reported since 687 BC; no other modern shower has been recorded as far back in time.[69]

The shower usually peaks on around April 22 and the morning of April 23. Counts typically range from 5 to 20 meteors per hour, averaging around 10.[68]

April Lyrid meteors are usually around magnitude +2. However, some meteors can be brighter, known as "Lyrid fireballs", cast shadows for a split second and leave behind smokey debris trails that last minutes.[70]

Occasionally, the shower intensifies when the planets steer the one-revolution dust trail of the comet into Earth's path, an event that happens about once every 60 years.[24]

The one-revolution dust trail is dust that has completed one orbit: the stream of dust released in the return of the comet prior to the current 1862 return. This mechanism replaces earlier ideas that the outbursts were due to a cloud of dust moving in a 60-year orbit.[71]

In 1982, amateur astronomers counted 90 April Lyrids per hour at the peak and similar rates were seen in 1922. A stronger storm of up to 700 per hour occurred in 1803,[72] observed by a journalist in Richmond, Virginia:

"Shooting stars. This electrical [sic] phenomenon was observed on Wednesday morning last at Richmond and its vicinity, in a manner that alarmed many, and astonished every person that beheld it. From one until three in the morning, those starry meteors seemed to fall from every point in the heavens, in such numbers as to resemble a shower of sky rockets ...[70]"[72]

The oldest known outburst, the shower on March 23.7,[73] 687 BC (proleptic Julian calendar) was recorded in Zuo Zhuan, which describes the shower as "On the 4th month in the summer in the year of Sexagenary cycle (xīn-mǎo) (of year 7 of King Zhuang of the State of Lu), at night, (the sky is so bright that some) fixed stars become invisible (because of the meteor shower); at midnight, stars fell like rain."[74] In the Australian Aboriginal astronomy of the Boorong tribe, the Lyrids represent the scratchings of the Mallee fowl (represented by Vega), coinciding with its nest-building season.[75]

Monocerotids[edit]

"Monocerotids is a reliable minor meteor shower that takes place from December 20th to December 7th and peaks on December 9th."[76]

Parent body: C/1917 F1 (Mellish).[77]

Alpha Monocerotids[edit]

This picture is of the Alpha-Monocerotid meteor outburst in 1995. It is a timed exposure where the meteors have actually occurred several seconds to several minutes apart. Credit: NASA Ames Research Center/S. Molau and P. Jenniskens.

Most years, those trails would miss the Earth altogether, but in some years the Earth is showered by meteors. This effect was first demonstrated from observations of the 1995 alpha Monocerotids,[78][79]

The swarm is visible every year from 15 to 25 November; its peak occurs on 21 or 22 November.[79]

The speed of its meteors is 65 km/s.[79]

Normally it has a low Zenithal Hourly Rate (ZHR), but occasionally it produces remarkable meteor storms that last less than an hour: such outbursts were observed in 1925, 1935, 1985, and 1995.[79]

The 1995 return was predicted based on the hypothesis that these outbursts were caused by the dust trail of a long period comet occasionally wandering in Earth's path due to planetary perturbations, during observations in southern Spain, assisted by a team of observers of the Dutch Meteor Society, and confirmed the brevity of Alpha Monocerotids outbursts as less than one hour, where the parent body, probably a long-period comet, is unknown.[79]

Gamma Normids[edit]

Discovery date = 1929[80]

Right ascension = 16h 24m, Declination = -51°[81]

Date of peak = March 15[80] Velocity = 68 km/s[81] Zenithal hourly rate = <1-2[81]

The first observations were made by R A McIntosh from Auckland, New Zealand in 1929, with confirmation coming from observations made by M. Geddes in 1932.[80] The shower was virtually ignored until radar equipment used by A A Weiss in Adelaide, South Australia detected activity 15–16 March 1953.[80] An attempt to observe the shower with radar in 1956 was unsuccessful, however the shower was observed again with radar in 1969.[80]

Members of the Western Australia Meteor Section made extensive observations in the 1970s and 1980s. In 1983 the average magnitude of the 63 meteors was 2.68 and 9.5% had trains with the highest Zenithal Hourly Rate (ZHR) of 9.6±2.3 recorded on the night of March 13/14. In 1986 273 meteors were observed, and the highest ZHR (3.49) was recorded on March 14/15. Nearly 20% of the meteors left trains.[80]

In 2005 the Liga IberoAmericana De Astronomía noted meteors from this stream every night during the observation period of March 8–17. The highest number of meteors seen was 5, on the night of March 10/11 with a ZHR of 14 ± 6.[80]

Orionids[edit]

Two Orionids meteors and the Milky Way are shown. Credit: Brocken Inaglory.{{free media}}

"The Orionid meteor shower [leftover bits of Halley's Comet] is scheduled to reach its maximum before sunrise on Sunday morning (Oct. 21 [2012]). This will be an excellent year to look for the Orionids, since the moon will set around 11 p.m. local time on Saturday night (Oct. 20) and will not be a hindrance at all ... The orbit of Halley's Comet closely approaches the Earth's orbit at two places. One point is in the early part of May producing a meteor display known as the Eta Aquarids. The other point comes in the middle to latter part of October, producing the Orionids."[82]

Perseids[edit]

Perseid meteor shower is from September 6 and 7, 1880-81. Credit: unknown.{{free media}}
A Perseid shower occurs in 2007. Credit: Brocken Inaglory.
Animation of 109P/Swift–Tuttle orbit from 1875 to 2100.
   Sun ·   Earth ·    Jupiter  ·   Saturn ·   Uranus ·   109P/Swift–Tuttle. Credit: Phoenix7777.{{free media}}
Radiant point is from August 8, 2006. Credit: Olga Berrios.{{free media}}

In 1835, Adolphe Quetelet identified the shower as emanating from the constellation Perseus.[83][8]

Right ascension = 03h 04m[84] and Declination = +58°[84]

The Perseid meteor shower, usually the richest meteor shower of the year, peaks in August. Over the course of an hour, a person watching a clear sky from a dark location might see as many as 50-100 meteors. Parent body is Comet Swift–Tuttle.[84] The first record is from 36 CE.[83][8]

The radiant point image on the right is from September 6 and 7, 1880-81.[85]

Velocity = 58 km/s[48] and Zenithal hourly rate = 100[84].

The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift–Tuttle. The cloud consists of particles ejected by the comet as it travels on its 133-year orbit.[86] Most of the particles have been part of the cloud for around a thousand years. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1865, which can give an early mini-peak the day before the maximum shower.[87] The dimensions of the cloud in the vicinity of the Earth are estimated to be approximately 0.1 AU across and 0.8 AU along the latter's orbit, spread out by annual interactions with the Earth's gravity.[88]

The shower is visible from mid-July each year, with the peak in activity between 9 and 14 August, depending on the particular location of the stream. During the peak, the rate of meteors reaches 60 or more per hour. They can be seen all across the sky; however, because of the shower's radiant in the constellation of Perseus, the Perseids are primarily visible in the Northern Hemisphere.[89] As with many meteor showers the visible rate is greatest in the pre-dawn hours, since more meteoroids are scooped up by the side of the Earth moving forward into the stream, corresponding to local times between midnight and noon, as can be seen in the accompanying diagram.[90] While many meteors arrive between dawn and noon, they are usually not visible due to daylight. Some can also be seen before midnight, often grazing the Earth's atmosphere to produce long bright trails and sometimes fireballs. Most Perseids burn up in the atmosphere while at heights above 80 kilometres (50 mi).[91]

Phoenicids[edit]

The Phoenicids get their name from the location of their radiant, which is in the constellation Phoenix, active from 29 November to 9 December, with a peak occurring around 5/6 December each year,[92] and are best seen from the Southern Hemisphere.

The Phoenicids appear to be associated with a stream of material from the disintegrating comet D/1819 W1 (Blanpain).[93]

A very minor meteor shower with a radiant in Phoenix also occurs in July; this shower is referred to as the July Phoenicids.[94]

Pi Puppids[edit]

"The Pi Puppids are a meteor shower associated with the comet 26P/Grigg-Skjellerup."[95]

"The Pi Puppids get their name because their radiant appears to lie in the constellation Puppis, at around Right ascension 112 degrees and Declination -45 degrees."[95]

Quadrantids[edit]

The Quadrantids (QUA) are a January meteor shower, with the zenithal hourly rate (ZHR) of this shower as high as that of two other reliably rich meteor showers, the Perseids in August and the Geminids in December.[96]

The meteor rates exceed one-half of their highest value for only about eight hours (compared to two days for the August Perseids), which means that the stream of particles that produces this shower is narrow, and apparently deriving within the last 500 years from some orbiting body.[97] The parent body of the Quadrantids was tentatively identified in 2003[98] as the minor planet (196256) 2003 EH1, which in turn may be related to the comet C/1490 Y1[99] that was observed by Chinese, Japanese and Korean astronomers some 500 years ago.

Beta Taurids[edit]

The Beta Taurids are normally active from June 5 to July 18.[8] They emanate from an average radiant of right ascension 5h18m, declination +21.2 and exhibit maximum activity around June 28–29 (Solar Longitude=98.3 deg). The sun has a solar longitude (λ⊙) of 90 degress on June 21 (Summer solstice) and as there are 365 days/year moves roughly 1 degree/day. The meteor shower radiant of RA=79.4 degrees converts to 5h 18m as each hour is 15 degrees. The Zenithal Hourly Rate typically reaches about 25 km/s as seen on radar.[8] Non-radio observers are faced with a very difficult prospect, because the Beta Taurid radiant is just 10–15 degrees west of the Sun on June 28.[100][101]

Asteroids associated with the β–Taurids include 2201 Oljato, 5143 Heracles, 6063 Jason, (8201) 1994 AH2 and 1991 BA.[102]

2019 will be the closest post-perihelion encounter with Earth since 1975. The Taurid swarm is expected to pass 0.06 AU (9,000,000 km; 5,600,000 mi) below the ecliptic between June 23 – July 17.[103]

During 2019 astronomers hope to search for hypothesized asteroids ~100 meters in diameter from the Taurid swarm between July 5–11, and July 21 – August 10.[104] There is circumstantial evidence that the daytime June 30 Tunguska event came from the same direction in the sky as the Beta Taurids.[104] The next June close approach to the Taurid swarm is expected in 2036.[105]

Northern Taurids[edit]

11/6/2015 - Image shows the Taurid Meteor Shower - Joshua Tree , CA. Credit: Channone Arif.{{free media}}

Parent body = 2004 TG10[106][84]

Radiant point = RA 03h 52m Dec = +22°.[107]

Occurs during October 20 – December 10, with a peak at 12 November.[107]

Velocity = 29 km/s.[107]

Zenithal hourly rate is 5.[107]

The Northern Taurids originated from the asteroid 2004 TG10.[108]

The Taurids are also made up of weightier material, pebbles instead of dust grains.[109]

Typically, Taurids appear at a rate of about 5 per hour, moving slowly across the sky at about 28 km/s (17 mi/s), or 100,800 km/h (65,000 mph).[109] If larger than a pebble, these meteors may become bolides as bright as the moon and leave behind smoke trails.[109]

The Beta Taurids could be the cause of the Tunguska event of June 30, 1908.[110]

In 1962 and 1963, the Mars 1 probe recorded one micrometeorite strike every two minutes at altitudes ranging from 6,000 to 40,000 km (3,700 to 24,900 mi) from Earth's surface due to the Taurids meteor shower, and also recorded similar densities at distances from 20 to 40 million kilometres (12,000,000 to 25,000,000 mi) from Earth.[111][112]

The Taurid stream has a cycle of activity that peaks roughly every 2,500 to 3,000 years,[110] when the core of the stream passes nearer to Earth and produces more intense showers. In fact, because of the separate "branches" (night-time in one part of the year and daytime in another; and Northern/Southern in each case) there are two (possibly overlapping) peaks separated by a few centuries, every 3000 years. The next peak is expected around 3000 AD.[110]

Over Poland in 1995, all-sky cameras imaged an absolute magnitude –17 Taurid bolide that was estimated to be 900 kg and perhaps a meter in diameter.[113]

In 1993, it was predicted that there would be a swarm of activity in 2005.[109] Around Halloween in 2005, many fireballs were witnessed that affected people's night vision.[109] Astronomers have taken to calling these the "Halloween fireballs."[109] The Tunguska event may have been caused by a Beta Taurid.[114]

A brief flash of light from a lunar impact event was recorded on November 7, 2005, while testing a new 250 mm (10 in) telescope and video camera built to monitor the Moon for meteor strikes.[115] This may be the first photographic record of such a strike.[116]

Southern Taurids[edit]

During the Southern Taurid meteor shower in 2013, fireball sightings were spotted over southern California, Arizona, Nevada, and Utah.[117]

The Southern Taurids originated from Comet Encke, while the Northern Taurids originated from the asteroid 2004 TG10.[118]

Encke and the Taurids are believed to be remnants of a much larger comet, which has disintegrated over the past 20,000 to 30,000 years.[119]

Gamma Ursae Minorids[edit]

Dates of occurrence 15 Jan - 25 Jan, with a peak (as of 2017) on 20 Jan, Celestial longitude of 299 , RA 15.2 Dec +67, speed = 31 km/s speed, ZHR = 3.[120]

Ursids[edit]

The Ursids were probably discovered by William F. Denning who observed them for several years around the start of the 20th century.[121] While there were sporadic observations after, the first coordinated studies of shower didn't begin until Dr. A. Bečvář observed an outburst of 169 per hour in 1945.[8] Further observations in the 1970s and ongoing to current have established a relationship with comet 8P/Tuttle.[121]

Parent body = 8P/Tuttle.[121]

Right ascension = 14h 28m[84], Declination = +78°[84]

Constellation = Ursa Minor (near Kochab)

Occurs during December 17 – December 26.[121]

Date of peak = December 22.[121]

Velocity = 33 km/s.[122]

Zenithal hourly rate = 10.[121]

Eta Virginids[edit]

Parent body: D/1766 G1 (Helfenzrieder)?[123]

Mercury[edit]

Meteors or meteor showers have been discussed for most of the objects in the Solar System with an atmosphere: Mercury,[124]

Venus[edit]

Venus can receive meteor showers from P/Halley Stream.[125]

Earth crossers[edit]

The close approach of apollo asteroid 2007 VK184 was in May 2014. Credit: Osamu Ajiki (AstroArts) and Ron Baalke (JPL).

EC denotes Earth-crossing.[126]

"50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs".[126]

This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere. Credit: NASA/Planetary Science.

"This diagram [center] maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors, technically called "bolides" and commonly referred to as "fireballs". Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size."[127]

"A map released [...] by NASA's Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in the Earth's atmosphere with random distribution around the globe. Released to the scientific community, the map visualizes data gathered by U.S. government sensors from 1994 to 2013. The data indicate that Earth's atmosphere was impacted by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event which was the largest asteroid to hit Earth in this period."[127]

Apollo asteroids[edit]

This a diagram showing the Apollo asteroids, compared to the orbits of the terrestrial planets of the Solar System.
  Mars (M)
  Venus (V)   Mercury (H)
  Sun
  Apollo asteroids
  Earth (E)
Credit: AndrewBuck.
Photograph of the full disc of the asteroid 162173 Ryugu, as it appeared to the Hayabusa2 spacecraft's Optical Navigation Camera – Telescopic (ONC-T) at a distance of 20 kilometres (12 miles) at 03:50 UTC on 26 June 2018. Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.{{fairuse}}
Asteroid Bennu imaged by the OSIRIS-REx probe on arrival 3 December 2018. Credit: NASA/Goddard/University of Arizona.{{free media}}
Photo of 101955 Bennu was taken by the OSIRIS-REx probe on 3 December 2018. Credit: NASA/Goddard/University of Arizona.

Note that sizes and distances of bodies and orbits are not to scale in the image on the right.

As of 2015, the Apollo asteroid group includes a total of 6,923 known objects of which 991 are numbered (JPL SBDB).

Ryugu shown on the left was discovered on 10 May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.[128]

The asteroid was officially named "Ryugu" by the Minor Planet Center on 28 September 2015.[129]

Initial images taken by the Hayabusa-2 spacecraft on approach at a distance of 700 km were released on 14 June 2018 and revealed a diamond shaped body and confirmed its retrograde rotation.[130]

Between 17 and 18 June 2018, Hayabusa 2 went from 330 km to 240 km from Ryugu and captured a series of additional images from the closer approach.[131]

On 21 September 2018, the first two of these rovers, which will hop around the surface of the asteroid, were released from Hayabusa2.[132]

On September 22, 2018, JAXA confirmed the two rovers had successfully touched down on Ryugu's surface which marks the first time a mission has completed a successful landing on a fast-moving asteroid body.[133]

"This series of images [second down on the right] taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained the 36 2.2-millisecond frames over a period of four hours and 18 minutes."[134]

101955 Bennu (provisional designation 1999 RQ36[135], a C-type carbonaceous asteroid in the Apollo group discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) Project on September 11, 1999, is a potentially hazardous object that is listed on the Sentry monitoring system, Sentry Risk Table, with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale.[136] It has a cumulative 1-in-2,700 chance of impacting Earth between 2175 and 2199.[137][138]

101955 Bennu has a mean diameter of approximately 492 m (1,614 ft; 0.306 mi) and has been observed extensively with the Arecibo Observatory planetary radar and the Goldstone Deep Space Communications Complex NASA Deep Space Network.[139][140][141]

Asteroid Bennu has a roughly spheroidal shape, resembling a spinning top, with the direction of rotation about its axis retrograde with respect to its orbit and a fairly smooth shape with one prominent 10–20 m boulder on its surface, in the southern hemisphere.[138]

There is a well-defined ridge along the equator of asteroid Bennu that suggests that fine-grained regolith particles have accumulated in this area, possibly because of its low gravity and fast rotation.[138]

Observations of this minor planet by the Spitzer Space Telescope in 2007 gave an effective diameter of 484±10 m, which is in line with other studies. It has a low visible geometric albedo of 0.046±0.005. The thermal inertia was measured and found to vary by ±19% during each rotational period suggesting that the regolith grain size is moderate, ranging from several millimeters up to a centimeter, and evenly distributed. No emission from a potential dust coma has been detected around asteroid Bennu, which puts a limit of 106 g of dust within a radius of 4750 km.[142]

Astrometric observations between 1999 and 2013 have demonstrated that 101955 Bennu is influenced by the Yarkovsky effect, causing the semimajor axis to drift on average by 284±1.5 meters/year; analysis of the gravitational and thermal effects give a bulk density of ρ = 1,260±70 kg/m3, which is only slightly denser than water, the predicted macroporosity is 40±10%, suggesting that the interior has a rubble pile structure, with an estimated mass is 7.8±0.9×1010
 kg
.[143]

Photometric observations of Bennu in 2005 yielded a synodic rotation period of 4.2905±0.0065 h, a B-type asteroid classification, which is a sub-category of C-type asteroid or carbonaceous asteroids. Polarimetric observations show that Bennu belongs to the rare F-type asteroid or F subclass of carbonaceous asteroids, which is usually associated with cometary features.[144] Measurements over a range of phase angles show a phase function slope of 0.040 magnitudes per degree, which is similar to other near-Earth asteroids with low albedo.[145]

Asteroid Bennu's basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation into more complex minerals.[138] Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100 km, where simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the 495 Eulalia (Eulalia family).[146]

Subsequently, the orbit drifted as a result of the Yarkovsky effect and mean motion resonances with the giant planets, such as Jupiter and Saturn modified the asteroid, possibly changing its spin, shape, and surface features.[147]

A possible cometary origin for Bennu, based on similarities of its spectroscopic properties with known comets, with the estimated fraction of comets in the population of Near Earth asteroids is 8±5 %.[144]

Moon[edit]

As the Moon is in the neighborhood of Earth it can experience the same showers, but will have its own phenomena due to its lack of an atmosphere per se, such as vastly increasing its sodium tail.[148] NASA now maintains an ongoing database of observed impacts on the moon[149] maintained by the Marshall Space Flight Center whether from a shower or not.

Mars[edit]

Mars meteor is photographed by the MER Spirit rover. Credit: .

Mars, and thus its moons, is known to have meteor showers.[150]

Only the relatively slower motion of the meteoroids due to increased distance from the sun should marginally decrease meteor brightness. This is somewhat balanced in that the slower descent means that Martian meteors have more time in which to ablate.[151]

On March 7, 2004, the panoramic camera on Mars Exploration Rover Spirit recorded a streak shown in he image on the right which is now believed to have been caused by a meteor from a Martian meteor shower associated with comet 114P/Wiseman-Skiff. A strong display from this shower was expected on December 20, 2007. Other showers speculated about are a "Lambda Geminid" shower associated with the Eta Aquariids of Earth (i.e., both associated with Comet 1P/Halley), a "Beta Canis Major" shower associated with Comet 13P/Olbers, and "Draconids" from 5335 Damocles.[152]

Hypotheses[edit]

  1. All Zodiac constellations should have meteor showers.
  2. All constellations some 80-90° away from the Zodiac should not have meteor showers.

See also[edit]

References[edit]

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