C/2021 T4 (Lemmon)

C/2021 T4 (Lemmon) is an inbound long period comet discovered by the Mount Lemmon Observatory on 7 October 2021.[2] This passage through the planetary region of the Solar System will reduce the orbital period from millions of years to thousands of years.[1]

C/2021 T4 (Lemmon)
The comet on 21 December 2022, by ZTF
Discovery
Discovery date7 October 2021
Designations
CK21T040, C6131F2
Orbital characteristics
Observation arc1.7 years
Aphelion≈44,000 AU (inbound)[1]
≈2,200 AU (outbound)
Perihelion1.4823 AU
Eccentricity0.99970
Orbital periodmillions of years (inbound)[1]
≈36,000 years (outbound)
Inclination160.76°
257.79°
Argument of
periapsis		329.78°
Next perihelion31 July 2023
Earth MOID0.497 AU (74.4 million km)
Jupiter MOID0.869 AU (130.0 million km)
Comet total
magnitude (M1)		6.9

It has been south of the celestial equator since October 2022. On 13 June it was 1.5 degrees from magnitude 2 Beta Ceti. Closest approach to Earth was on 20 July 2023 at a distance of 0.54 AU (81 million km).[3] The next day it reached its southernmost declination, at -56 degrees. On 25 July it passed next to the globular cluster NGC 6397.[4] It reached perihelion on 31 July 2023 at a solar distance of 1.48 AU. The comet brightened to around apparent magnitude 8.[5]

References
  1. Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2021 T4 (Lemmon)". Retrieved 2023-04-26. (Solution using the Solar System's barycenter (Sun+Jupiter). Select Ephemeris Type:Elements and Center:@0) Epoch 1800 has PR= 1E+9 / 365.25 days = millions of years
  2. "MPEC 2021-U187 : COMET C/2021 T4 (Lemmon)". minorplanetcenter.net. Retrieved 2021-10-30.
  3. Earth Approach 2023 (delta. Close approach occurs when deldot flips from negative to positive.)
  4. Dickinson, David (25 July 2023). "A Fine Southern Apparition for Comet T4 Lemmon". Universe Today. Retrieved 29 July 2023.
  5. C/2021 T4 ( Lemmon ) mag chart by Seiichi Yoshida
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