Leonids

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Leonids
Zenithal hourly rate
15[3]
See also: List of meteor showers

The Leonids (

meteors appear to radiate from that point in the sky. Their proper Greek name should be Leontids (Λεοντίδαι, Leontídai), but the word was initially constructed as a Greek/Latin hybrid[citation needed] and it has been used since. The meteor shower peak should be on 17 November, but any outburst in 2023 is likely to be from the 1767 meteoroid stream.[6]

evaporate under the heat of the Sun when it is near the Sun – typically closer than Jupiter's orbit. Due to the retrograde orbit of 55P/Tempel–Tuttle, the Leonids are fast moving streams which encounter the path of Earth and impact at 70 km/s (43 mi/s).[3] It is the fastest annual meteor shower.[3] Larger Leonids which are about 10 mm (0.4 in) across have a mass of 0.5 g (0.02 oz) and are known for generating bright (apparent magnitude −1.5) meteors.[7]
An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet.

The meteoroids left by the comet are organized in trails in orbits similar to – though different from – that of the comet. They are differentially disturbed by the planets, in particular Jupiter,[8] and to a lesser extent by radiation pressure from the Sun – the Poynting–Robertson effect and the Yarkovsky effect.[9] These trails of meteoroids cause meteor showers when Earth encounters them. Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around 18 November, but some are spread through several days on either side and the specific peak changes every year. Conversely, young trails are spatially very dense and the cause of meteor outbursts when the Earth enters one.

The Leonids also produce meteor storms (very large outbursts) about every 33 years, during which activity exceeds 1,000 meteors per hour,[10] with some events exceeding 100,000 meteors per hour,[11] in contrast to the sporadic background (5 to 8 meteors per hour) and the shower background (several meteors per hour).

Meteoroids[7]
Size
Apparent Magnitude
Comparable in brightness
2 mm (0.08 in) +3.7 (visual)
Delta Ursae Majoris
10 mm (0.4 in) −1.5 (bright) Sirius
20 mm (0.8 in) −3.8 (Fireball) Venus

History

1800s

The Leonids are famous because their meteor showers, or storms, can be among the most spectacular. Because of the storm of 1833 and the developments in scientific thought of the time (see for example the identification of Halley's Comet), the Leonids have had a major effect on the scientific study of meteors, which had previously been thought to be atmospheric phenomena. Although it has been suggested the Leonid meteor shower and storms have been noted in ancient times,[12] it was the meteor storm of November 12-13, 1833 that broke into people's modern-day awareness. One estimate of the peak rate is over one hundred thousand meteors an hour,[13] while another, done as the storm abated, estimated in excess of 240,000 meteors during the nine hours of the storm,[1] over the entire region of North America east of the Rocky Mountains.

The event was marked by several nations of

Christ.[28] Though it was noted in the midwest and eastern areas, it was also noted in Far West, Missouri.[29]

American Journal of Science and Arts, published in January–April 1834,[30] and January 1836.[31] He noted the shower was of short duration and was not seen in Europe, and that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space.[32] Accounts of the 1866 repeat of the Leonids counted hundreds per minute/a few thousand per hour in Europe.[33] The Leonids were again seen in 1867, when moonlight reduced the rates to 1,000 meteors per hour. Another strong appearance of the Leonids in 1868 reached an intensity of 1,000 meteors per hour in dark skies. It was in 1866–67 that information on Comet Tempel-Tuttle was gathered, pointing it out as the source of the meteor shower and meteor storms.[32]
When the storms failed to return in 1899, it was generally thought that the dust had moved on and the storms were a thing of the past.

The November Meteors by Étienne Léopold Trouvelot, 1868

1900s

In 1966, a spectacular meteor storm was seen over the Americas.

Sky and Telescope.[38]
It showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the meteoroids are mostly behind and outside the path of the comet, but paths of the Earth through the cloud of particles resulting in powerful storms were very near paths of nearly no activity. But overall the 1998 Leonids were in a favorable position so interest was rising.

Leading up to the 1998 return, an airborne observing campaign was organized to mobilize modern observing techniques by Peter Jenniskens at NASA Ames Research Center.[39] In 1999, there were also efforts to observe impacts of meteoroids on the Moon, as an example of transient lunar phenomenon. A particular reason to observe the Moon is that our vantage from a location on Earth sees only meteors coming into the atmosphere relatively close to us, while impacts on the Moon would be visible from across the Moon in a single view.[40] The sodium tail of the Moon tripled just after the 1998 Leonid shower which was composed of larger meteoroids (which in the case of the Earth was witnessed as fireballs).[41] However, in 1999 the sodium tail of the Moon did not change from the Leonid impacts.

Research by Kondrat'eva, Reznikov and colleagues

Kazan University had shown how meteor storms could be accurately predicted, but for some years the worldwide meteor community remained largely unaware of these results. The work of David J. Asher, Armagh Observatory and Robert H. McNaught, Siding Spring Observatory[8] and independently by Esko Lyytinen[43][44] in 1999, following on from the Kazan research, is considered by most meteor experts as the breakthrough in modern analysis of meteor storms. Whereas previously it was hazardous to guess if there would be a storm or little activity, the predictions of Asher and McNaught timed bursts in activity down to ten minutes by narrowing down the clouds of particles to individual streams from each passage of the comet, and their trajectories amended by subsequent passage near planets. However, whether a specific meteoroid trail will be primarily composed of small or large particles, and thus the relative brightness of the meteors, was not understood. But McNaught did extend the work to examine the placement of the Moon with trails and saw a large chance of a storm impacting in 1999 from a trail while there were less direct impacts from trails in 2000 and 2001 (successive contact with trails through 2006 showed no hits).[41]

Leonids as seen from space in 1997, NASA

2000s

Viewing campaigns resulted in spectacular footage from the 1999, 2001, and 2002 storms which produced up to 3,000 Leonid meteors per hour.[39] Predictions for the Moon's Leonid impacts also noted that in 2000 the side of the Moon facing the stream was away from the Earth, but that impacts should be in number enough to raise a cloud of particles kicked off the Moon which could cause a detectable increase in the sodium tail of the Moon.[41] Research using the explanation of meteor trails/streams have explained the storms of the past. The 1833 storm was not due to the recent passage of the comet, but from a direct impact with the previous 1800 dust trail.[45] The meteoroids from the 1733 passage of Comet Tempel-Tuttle resulted in the 1866 storm[46] and the 1966 storm was from the 1899 passage of the comet.[47] The double spikes in Leonid activity in 2001 and in 2002 were due to the passage of the comet's dust ejected in 1767 and 1866.[48] This ground breaking work was soon applied to other meteor showers – for example the 2004 June Bootids. Peter Jenniskens has published predictions for the next 50 years.[49] However, a close encounter with Jupiter is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many decades. Recent work tries to take into account the roles of differences in parent bodies and the specifics of their orbits, ejection velocities off the solid mass of the core of a comet, radiation pressure from the Sun, the Poynting–Robertson effect, and the Yarkovsky effect on the particles of different sizes and rates of rotation to explain differences between meteor showers in terms of being predominantly fireballs or small meteors.[9]

Year Leonids active between Peak of shower
ZHRmax
2006 19 Nov. Outburst of ZHR=35–40 was predicted from the 1932 trail.[50] 78[51]
2007 19 Nov. Outburst of ZHR=~30 from the 1932 trail was predicted for 18 Nov.[50] 35[52]
2008 14–22 November 17 Nov.[39] Considerable outburst of ZHR=130 from the 1466 trail was predicted for 17 Nov.[50] 99[53]
2009 10–21 November ZHRmax ranging from 100[54][55] to over 500[39][56][57] on 17 Nov. The peak was observed at predicted time.[58] 79[58]
2010 10–23 November 18 Nov 32±4[59][60]
2011 6–30 November 18 Nov 22±3[59][61]
2012 6–30 November 20 Nov. Nov 17 ZHR=5–10 (predicted) / 20 Nov ZHR=10–15 (predicted from 1400 trail)[50] 47±11[59][62]
2013 15–20 November 17 Nov but was washed out by a Full moon on 17 Nov
2014 6–30 November 18 Nov 15±4[59][63]
2015 6–30 November 18 Nov[59] 15[64]
2016 6–30 November 17 Nov[65] 10–15[66]
2017 6–30 November 17 Nov[67] ~17[68]
2018 6–30 November 17 Nov[69] 15–20[70]
2019 6–30 November 17 Nov 10–15[71]
2020 6–30 November 17 Nov 10–15[72]
2021 6–30 November 17 Nov[73] 10–15[74]
2022 17-21 November 17 Nov (there was a low possibility of an outburst from the 1733 meteoroid stream on 19 November) 15 (predicted) - 300 (unlikely)[6]
2023 3 Nov - 2 Dec 17 Nov (a modest increase is possible from the 1767 meteoroid stream on 21 November)[6] 15 (predicted)[6]
2024 17 Nov 15–20 (predicted)[6]
2025 17 Nov (any outburst is likely to be from the 1699 meteoroid stream) 10–15 (predicted)[6]
2026 17 Nov 15 (predicted)[6]
2027 17 Nov (possible activity from 1167 meteoroid stream on 20 November) 40–50 (predicted)[6]
2028 17 Nov 30–40 (predicted)[6]
2029 17 Nov (possible activity from 1998 meteoroid stream) 30–40 (predicted)[6]
2030 17 Nov 15-20 (predicted)[6]
2031 17 Nov <10 (predicted)[75]
2032 17 Nov <10 (predicted)[75]
2033 17 Nov (Outburst likely from 1899 meteoroid stream. Encountering a younger stream typically generates more activity.) 35-400 (predicted)[75]
2034 17–18 Nov (probable outburst from the young 1932 meteoroid stream on 18 November) 40–500 (predicted)[75]
2061 (Possible outburst from the young 1998 meteoroid stream on 19 November) 50 (predicted) – 5100 (unlikely)[75]
2099 (Possible outburst from dense stream)[76] 1000+?

Predictions until the end of the 21st century have been published by Mikhail Maslov.[50]

See also

References

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Further reading

External links