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Early warning for newly discovered comets and unconfirmed objects.

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C/2021 A4

C/2021 A4 (NEOWISE)

CometClass Ecatalogued
Unknown

Not currently visible. Last report 1984 days ago at mag 33.8. Historic peak was mag 15.3. Typical backyard telescopes will not show it. HST, JWST, or an 8–10 m class telescope might recover it with a good ephemeris.

Active comet in COBS

JSONCSV

Right ascension

—

J2000

Declination

—

J2000

Estimated magnitude

33.8

Professional survey · COBS consensus

Confidence

33

Class E · priority 60

Observations

70

Arc unknown

Last observation

1984d ago

Mon, 12 Apr 2021 09:36:00 GMT · COBS consensus

Perihelion

2021-03-19

1.150 au

Peak window

2021-02-11 → 2021-03-22

COBS peak mag 15.3 on 2021-02-14 · perihelion 2021-03-19. Window is those dates ±3 days — not a light-curve fit.

Historic peak

15.3

COBS / analyzed peak 2021-02-14

Catalog ingest

11h ago

Venator last wrote this row 2026-09-16 13:20:19 UTC

Light curve

Brightness over time (V mag)

Gold = reported observations. Steel dashed family = ensemble (nominal / outburst / fade / disruption).

Tail length

Converted to degrees from COBS (d / arcmin / arcsec). Empty until analysis has pulled the archive.

Ensemble is a first-pass H0/n photometric model plus observed samples — not a trained ML forecast yet. The background analyzer walks the catalog one object at a time so COBS is not flooded. Disruption track rises after perihelion to stand in for solar-wind stripping.

Orbital elements

q

1.150 au

e

0.9730

i

112.00°

Ω

307.00°

ω

205.00°

a

—

MOID

—

H

—

H0 / n

—

NEO score

—

PHA score

—

RMS

—

Elongation

—

Reporting sources

  • COBS comet list

    ok

    Comet Observation Database magnitudes and perihelion data for the full COBS list (active and inactive).

Name history

  • C/2021 A4 (NEOWISE)

    Informal: NEOWISE

    C/2021 A4 · 2026-09-14 18:28:00 UTC → current

Discoverers

  • NEOWISE

    Discoverer · parsed-name · 2026-09-14 18:28:00 UTC → current

Contributors

Pips are observation weight on this object (log of report count). Hover for catalog-wide weight.