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On 10 October the comet showed a short but dense dust [[comet tail|tail]].<ref>{{Cite web|date=2021-10-13|title=How Bright Will Comet Leonard Get?|url=https://skyandtelescope.org/astronomy-news/how-bright-will-comet-leonard-get/|access-date=2021-10-20|website=Sky & Telescope|language=en-US}}</ref> In early December the comet had an [[apparent magnitude]] (coma+nucleus) of around 6.<ref name=vanbuitenen/> The first reports of naked-eye observations by experienced observers started coming in on 5 December 2021.<ref>[https://twitter.com/martinastro2005/status/1467467074331099136 Martin McKenna naked eye]</ref> Much like observing [[Messier 33]], the low [[surface brightness]] of the comet can make it difficult to observe near [[urban area]]s. On the morning of 6 December 2021 the comet was about 5 degrees from the star [[Arcturus]]. On 14 December 2021 the comet was 14.7 degrees from the Sun<ref name=sol-elong/> and quickly became better seen from the southern hemisphere.
On 10 October the comet showed a short but dense dust [[comet tail|tail]].<ref>{{Cite web|date=2021-10-13|title=How Bright Will Comet Leonard Get?|url=https://skyandtelescope.org/astronomy-news/how-bright-will-comet-leonard-get/|access-date=2021-10-20|website=Sky & Telescope|language=en-US}}</ref> In early December the comet had an [[apparent magnitude]] (coma+nucleus) of around 6.<ref name=vanbuitenen/> The first reports of naked-eye observations by experienced observers started coming in on 5 December 2021.<ref>[https://twitter.com/martinastro2005/status/1467467074331099136 Martin McKenna naked eye]</ref> Much like observing [[Messier 33]], the low [[surface brightness]] of the comet can make it difficult to observe near [[urban area]]s. On the morning of 6 December 2021 the comet was about 5 degrees from the star [[Arcturus]]. On 14 December 2021 the comet was 14.7 degrees from the Sun<ref name=sol-elong/> and quickly became better seen from the southern hemisphere.


The [[forward scatter]]ing of light helped the comet to briefly brighten to as much as magnitude 2.5,<ref name="vanbuitenen"/><ref name=Yoshida/><ref>[https://twitter.com/aciqra/status/1471356456922320897 Qiсһеng Ζһаng from Pasadena on 14 Dec 2021]</ref> but was also enhanced by a modest outburst.<ref name=COBS>[https://cobs.si/show?id=679 What happened to C/2021 A1 (Leonard)?]</ref> The comet experienced outbursts on December 15, 20 and 23, thus reaching third magnitude before dimming back to 4th magnitude. The ion tail of the comet appeared complex, with knots and steamers.<ref name="chistmasskyandtelescope">{{cite web |title=Comet Leonard: A Gift at Christmastime |url=https://skyandtelescope.org/astronomy-news/comet-leonard-a-gift-at-christmastime/ |website=Sky & Telescope |access-date=17 January 2022 |date=25 December 2021}}</ref> In stacked photos the tail could be traced for 60 degrees in the sky.<ref>{{cite web |title=APOD: 2021 December 30 - The Further Tail of Comet Leonard |url=https://apod.nasa.gov/apod/ap211230.html |website=apod.nasa.gov |access-date=17 January 2022}}</ref> While the comet is lower in the sky, [[atmospheric extinction]] will offset much of the brightening. As of 22 December 2021, the comet was around apparent magnitude 4, making it a good [[binoculars|binocular]] comet for the Southern hemisphere.<ref name="vanbuitenen"/><ref name="chistmasskyandtelescope"/> It was the brightest comet of 2021.<ref name="disintegrated"/>
The [[forward scatter]]ing of light helped the comet to briefly brighten to as much as magnitude 2.5,<ref name="vanbuitenen"/><ref name=Yoshida/><ref>[https://twitter.com/aciqra/status/1471356456922320897 Qiсһеng Ζһаng from Pasadena on 14 Dec 2021]</ref> but was also enhanced by a modest outburst.<ref name=COBS>[https://cobs.si/show?id=679 What happened to C/2021 A1 (Leonard)?]</ref> The comet experienced outbursts on December 15, 20 and 23, thus reaching third magnitude before dimming back to 4th magnitude. The ion tail of the comet appeared complex, with knots and steamers.<ref name="chistmasskyandtelescope">{{cite web |title=Comet Leonard: A Gift at Christmastime |url=https://skyandtelescope.org/astronomy-news/comet-leonard-a-gift-at-christmastime/ |website=Sky & Telescope |access-date=17 January 2022 |date=25 December 2021}}</ref> In stacked photos the tail could be traced for 60 degrees in the sky.<ref>{{cite web |title=APOD: 2021 December 30 - The Further Tail of Comet Leonard |url=https://apod.nasa.gov/apod/ap211230.html |website=apod.nasa.gov |access-date=17 January 2022}}</ref> While the comet was lower in the sky, [[atmospheric extinction]] offset much of the brightening.{{cn|date=April 2022}} As of 22 December 2021, the comet was around apparent magnitude 4, making it a good [[binoculars|binocular]] comet for the Southern hemisphere.<ref name="vanbuitenen"/><ref name="chistmasskyandtelescope"/> It was the brightest comet of 2021.<ref name="disintegrated"/>


On 23 February 2022 the comet was observed with the [[Slooh|SLOOH]] telescope in Chile, operated by Martin Masek. The comet lacked a central concetration, which indicates that the nucleus of the comet disintegrated or evaporated completely. Further observations confirmed the lack of concetration.<ref name="disintegrated">{{cite web |last1=Machholz |first1=Donald |title=Comet Leonard has disintegrated |url=https://earthsky.org/space/comet-leonard-has-disintegrated/ |website=earthsky.org |access-date=22 March 2022 |date=21 March 2022}}</ref>
On 23 February 2022 the comet was observed with the [[Slooh|SLOOH]] telescope in Chile, operated by Martin Masek. The comet lacked a central concetration, which indicates that the nucleus of the comet disintegrated or evaporated completely. Further observations confirmed the lack of concetration.<ref name="disintegrated">{{cite web |last1=Machholz |first1=Donald |title=Comet Leonard has disintegrated |url=https://earthsky.org/space/comet-leonard-has-disintegrated/ |website=earthsky.org |access-date=22 March 2022 |date=21 March 2022}}</ref>

Revision as of 02:07, 11 April 2022

C/2021 A1 (Leonard)
C/2021 A1 (Leonard) on December 28, 2021
Discovery
Discovered byGreg J. Leonard
Discovery date3 January 2021[1]
Designations
C4AGJ62
Orbital characteristics
Orbit typelong period (inbound)
hyperbolic (outbound)
Aphelion≈3700 AU (barycentric epoch 1950)[2]
Perihelion0.6151 AU
Eccentricity0.99966 (barycentric epoch 1950)[2]
1.00004 (barycentric epoch 2100)
Orbital period≈80000 yr (inbound)[2]
Inclination132.68°
Last perihelion3 January 2022
Earth MOID0.231 AU (34.6 million km)[3]
Jupiter MOID0.296 AU (44.3 million km)
Comet total
magnitude (M1)		5.3

C/2021 A1 (Leonard) was a long period comet[4] that was discovered by G. J. Leonard at the Mount Lemmon Observatory on 3 January 2021 (a year before perihelion) when the comet was 5 AU (750 million km) from the Sun.[1] It had a retrograde orbit. The nucleus was about 1 km (0.6 mi) across. It came within 4 million km (2.5 million mi) of Venus, the closest-known cometary approach to Venus.[5]

Observational history

The comet was discovered by G. J. Leonard at the Mount Lemmon Observatory on 3 January 2021 (a year before perihelion) when the comet was 5 AU (750 million km) from the Sun. The comet appeared to have a 10" coma and a 5" broad tail in the photographs taken as part of the Mt. Lemmon Survey and its magnitude was estimated to be 19.0. Precovery images dated back to April 11, 2020.[1]

On 10 October the comet showed a short but dense dust tail.[6] In early December the comet had an apparent magnitude (coma+nucleus) of around 6.[7] The first reports of naked-eye observations by experienced observers started coming in on 5 December 2021.[8] Much like observing Messier 33, the low surface brightness of the comet can make it difficult to observe near urban areas. On the morning of 6 December 2021 the comet was about 5 degrees from the star Arcturus. On 14 December 2021 the comet was 14.7 degrees from the Sun[9] and quickly became better seen from the southern hemisphere.

The forward scattering of light helped the comet to briefly brighten to as much as magnitude 2.5,[7][10][11] but was also enhanced by a modest outburst.[12] The comet experienced outbursts on December 15, 20 and 23, thus reaching third magnitude before dimming back to 4th magnitude. The ion tail of the comet appeared complex, with knots and steamers.[13] In stacked photos the tail could be traced for 60 degrees in the sky.[14] While the comet was lower in the sky, atmospheric extinction offset much of the brightening.[citation needed] As of 22 December 2021, the comet was around apparent magnitude 4, making it a good binocular comet for the Southern hemisphere.[7][13] It was the brightest comet of 2021.[15]

On 23 February 2022 the comet was observed with the SLOOH telescope in Chile, operated by Martin Masek. The comet lacked a central concetration, which indicates that the nucleus of the comet disintegrated or evaporated completely. Further observations confirmed the lack of concetration.[15]

Orbit

Animation of C／2021 A1's orbit around Sun - 2021 close approach
   C/2021 A1 ·   Sun ·   Mercury  ·   Venus ·   Earth ·   Mars

C/2021 A1 has been inside of the orbit of Neptune since May 2009.[16] Using an epoch of 1950 which is well before the comet entered the planetary region of the Solar System, a barycentric orbit solution suggests the comet had an approximately 80,000-year orbital period.[2] Thus, the comet has spent the last 40,000 years inbound from approximately 3,700 AU (550 billion km). After perihelion, the comet will be ejected from the Solar System. The barycentric orbit will remain hyperbolic after September 2022.[2]

On 12 December 2021 the comet was 0.233 AU (34.9 million km) from Earth and on 18 December 2021 it was 0.028 AU (4.2 million km) from Venus.[3] It made its closest approach to the Sun on 3 January 2022.

  • Conjunction of Comet C/2021 A1 and Messier 3, captured on 3 Dec 2021 from Summerville, SC
    Conjunction of Comet C/2021 A1 and Messier 3, captured on 3 Dec 2021 from Summerville, SC
  • Wide angle view of C/2021 A1 on December 28, 2021
    Wide angle view of C/2021 A1 on December 28, 2021
  • The comet over Tenerife on 31 December 2021
    The comet over Tenerife on 31 December 2021
  • Comet Leonard on January 2, 2022, one day before perihelion
    Comet Leonard on January 2, 2022, one day before perihelion

See also

References

  1. ^ a b c "MPEC 2021-A99 : COMET C/2021 A1 (Leonard)". Minor Planet Center. Retrieved 2021-01-10.
  2. ^ a b c d e Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2021 A1 (Leonard)". Retrieved 2021-01-13. (Solution using the Solar System's barycenter (Sun+Jupiter). Select Ephemeris Type:Elements and Center:@0) Epoch 1950 has PR= 2.91E+07 / 365.25 = 79700 years
  3. ^ a b "JPL Small-Body Database Browser: C/2021 A1". JPL. Retrieved 2021-09-29.
  4. ^ CBET 4907: original 1/a = +0.000575 (long-period) and future 1/a = -0.000030 (hyperbolic). The orbital energy is inversely proportional to negative semi-major axis. Objects in hyperbolic orbits have negative semi major axis, giving them a positive orbital energy.
  5. ^ Weule, Genelle (8 December 2021). "Astronomers anxiously watch Comet Leonard to see if it will live up to predictions as a Christmas treat over Australia". ABC News. Australian Broadcasting Corporation. Retrieved 8 December 2021.
  6. ^ "How Bright Will Comet Leonard Get?". Sky & Telescope. 2021-10-13. Retrieved 2021-10-20.
  7. ^ a b c "C/2021 A1 (Leonard)". Gideon van Buitenen. Retrieved 2021-11-16.
  8. ^ Martin McKenna naked eye
  9. ^ Horizons output. "Solar elongation Comet C/2021 A1 (Leonard) in mid-December 2021". Retrieved 2021-10-17. Sun-Observer-Target (S-O-T)
  10. ^ Magnitude estimate – Seiichi Yoshida
  11. ^ Qiсһеng Ζһаng from Pasadena on 14 Dec 2021
  12. ^ What happened to C/2021 A1 (Leonard)?
  13. ^ a b "Comet Leonard: A Gift at Christmastime". Sky & Telescope. 25 December 2021. Retrieved 17 January 2022.
  14. ^ "APOD: 2021 December 30 - The Further Tail of Comet Leonard". apod.nasa.gov. Retrieved 17 January 2022.
  15. ^ a b Machholz, Donald (21 March 2022). "Comet Leonard has disintegrated". earthsky.org. Retrieved 22 March 2022.
  16. ^ Neptune has perihelion (closest approach to the Sun) at 29.8 AU. C/2021 A1 has been inside that distance since May 2009.
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