Editing Leonids (section)

{{Short description|Meteor shower associated with the comet Tempel–Tuttle}}
{{Other uses|Leonid (disambiguation)}}
{{Use dmy dates|date=October 2020}}
{{Infobox meteor shower
| name          = Leonids
| image         = [[File:Leonid Meteor.jpg|245px]]
| caption       = A Leonid meteor during the peak of the Leonids in 2009
| pronounce     = {{IPAc-en|ˈ|l|iː|ən|ɪ|d|z}}
| date          = 902 AD (first record)<ref name=MAC/>
| parent        = [[55P/Tempel–Tuttle]]<ref name=moore_rees2011/>
<!-- Radiant -->
| constellation = [[Leo (constellation)|Leo]]
| ra            = {{RA|10|17}}<ref name="AMS2023"/>
| dec           = {{DEC|+21.6}}<ref name="AMS2023"/>
<!-- Properties -->
| month         = {{nowrap|3 November – 2 December}}<ref name="AMS2023"/>
| peak          = 17&nbsp;November
| velocity      = 70–71<ref name="AMS2023"/><ref name=aj116_1_499/>
| zhr           = 15<ref name="AMS2023"/>
| notes         = 
}}

The '''Leonids''' ({{IPAc-en|ˈ|l|iː|ən|ɪ|d|z}} {{respell|LEE|ə-nidz}}) are a prolific annual [[meteor shower]] associated with the [[comet]] [[55P/Tempel–Tuttle|Tempel–Tuttle]], and are also known for their spectacular meteor storms that occur about every 33 years.<ref name="2019 Leonids">{{cite web |last=Byrd |first=Deborah |title=All you need to know: 2019's Leonid meteor shower |url=https://earthsky.org/?p=29831 |url-status=live |publisher=EarthSky |date=15 November 2018 |access-date=26 February 2019 |archive-url=https://web.archive.org/web/20191111225720/https://earthsky.org/?p=29831 |archive-date=11 November 2019}}</ref> The Leonids get their name from the location of their [[Radiant (meteor shower)|radiant]] in the [[constellation]] [[Leo (constellation)|Leo]]: the [[meteor]]s appear to radiate from that point in the [[sky]]. The name is derived from [[Greek language|Greek]] and [[Latin|Latin]] with the prefix ''Leo-'' referring to the constellation and the suffix ''-ids'' signifying that the meteor shower is the offspring of, descendent of, the constellation Leo. <ref name="Dictionary.com">{{cite web|url=https://www.dictionary.com/browse/id#american-id-2-definitions|title=Id|author=dictionary.com|publisher=dictionary.com|date=12 February 2025|access-date=12 February 2025|archive-date=7 February 2025|archive-url= https://web.archive.org/web/20250207000614/https://www.dictionary.com/browse/id#american-id-2-definitions|url-status=live}}</ref>

[[Earth]] moves through meteoroid streams left from passages of a comet. The streams consist of solid particles, known as [[meteoroid]]s, normally ejected by the comet as its frozen gases [[evaporate]] under the heat of the [[Sun]] once within Jupiter's orbit. Due to the [[Retrograde and prograde motion|retrograde orbit]] of 55P/Tempel–Tuttle, the Leonids are fast moving streams which encounter the path of Earth and impact at {{cvt|70|km/s}}.<ref name="AMS2023"/> It is the fastest annual meteor shower.<ref name="AMS2023"/> Larger Leonids which are about {{cvt|10|mm|sigfig=1}} across have a mass of {{cvt|0.5|g|oz|sigfig=1}} and are known for generating bright ([[apparent magnitude]] −1.5) meteors.<ref name=jenniskens2006/> 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{{snd}}though different from{{snd}}that of the comet. They are differentially disturbed by the planets, in particular [[Jupiter]],<ref name="Asher&McNaught99">{{cite journal |last1=McNaught |first1=Robert H. |author1-link=Robert H. McNaught | last2 = Asher | first2 = David J. | author2-link = David J. Asher | title = Leonid Dust Trails and Meteor Storms | journal = WGN, Journal of the International Meteor Organization | volume = 27 | issue = 2 | pages = 85–102 | date = 1999 |bibcode = 1999JIMO...27...85M}}</ref> and to a lesser extent by [[radiation pressure]] from the Sun{{snd}}the [[Poynting–Robertson effect]] and the [[Yarkovsky effect]].<ref name="BrownThesis">{{cite thesis |last=Brown |first=Peter Gordon |title=Evolution of Two periodic Meteoroid Streams: the Perseids and Leonids |url=http://aquarid.physics.uwo.ca/~pbrown/thesis.html |url-status=live |year=1999 |page=4005 |access-date=24 December 2009 |bibcode=1999PhDT.........7B |archive-url=https://web.archive.org/web/20100605010213/http://aquarid.physics.uwo.ca/~pbrown/thesis.html |archive-date=5 June 2010}}</ref> 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 {{em|meteor storms}} (very large outbursts) about every 33 years, during which activity exceeds 1,000 meteors per hour,<ref>{{cite web|url=https://www.cbsnews.com/news/leonids-meteor-shower-2019-will-light-up-the-sky-heres-how-to-watch/|title=Leonids meteor shower will soon light up the sky. Here's how to watch.|author=Sophie Lewis|publisher=CBS News|date=16 November 2019|access-date=18 August 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031231913/https://www.cbsnews.com/news/leonids-meteor-shower-2019-will-light-up-the-sky-heres-how-to-watch/|url-status=live}}</ref> with some events exceeding 100,000 meteors per hour,<ref>{{cite news|url=https://www.washingtonpost.com/weather/2019/11/18/leonid-shower-dud-past-years-have-featured-extreme-meteor-storms/|title=Leonid shower a dud in 2019, but past years have featured extreme 'meteor storms'|author=Matthew Cappucci|newspaper=[[The Washington Post]]|date=18 November 2019|access-date=18 August 2020|archive-date=26 September 2020|archive-url=https://web.archive.org/web/20200926175816/https://www.washingtonpost.com/weather/2019/11/18/leonid-shower-dud-past-years-have-featured-extreme-meteor-storms/|url-status=live}}</ref> in contrast to the sporadic background (5 to 8 meteors per hour) and the shower background (several meteors per hour).

{| class="wikitable" style="font-size: 0.9em"
|+Meteoroids<ref name=jenniskens2006/>
! Size
! [[Apparent Magnitude]]
! Comparable in brightness
|-
| {{convert|2|mm|sigfig=1|abbr=on}} || +3.7 (visual) || [[Delta Ursae Majoris]]
|-
| {{convert|10|mm|sigfig=1|abbr=on}} || [[Apparent_magnitude#Sirius|−1.5]] (bright) || [[Sirius]]
|-
| {{convert|20|mm|sigfig=1|abbr=on}} || −3.8 ([[Meteoroid#Fireball|Fireball]]) || [[Venus]]
|}