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Early warning for newly discovered comets and unconfirmed objects.

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C/2023 H5

C/2023 H5 (Lemmon)

CometClass Ecatalogued
Southern hemisphere

Not visible to typical instruments. Current estimate mag 18.1. Historic peak was mag 16.3. Visual and most CCD amateur setups will not see it. Space telescopes or large ground telescopes are the remaining path.

Active comet in COBS

JSONCSV

Right ascension

00h 50m 37s

J2000

Declination

−70° 07′ 54″

J2000

Estimated magnitude

18.1

Professional survey · COBS consensus

Confidence

33

Class E · priority 60

Observations

297

Arc unknown

Last observation

10d ago

Sun, 06 Sep 2026 19:55:12 GMT · COBS consensus

Perihelion

2025-06-30

4.310 au

Peak window

2025-03-01 → 2025-07-03

COBS peak mag 16.3 on 2025-03-04 · perihelion 2025-06-30. Window is those dates ±3 days — not a light-curve fit.

Historic peak

16.3

COBS / analyzed peak 2025-03-04

Catalog ingest

14m ago

Venator last wrote this row 2026-09-16 22:00:04 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

4.310 au

e

1.0000

i

97.90°

Ω

159.00°

ω

60.10°

a

-5560.000 au

MOID

—

H

—

H0 / n

2.2 / 7.2

NEO score

—

PHA score

—

RMS

—

Elongation

111°

Reporting sources

  • COBS comet list

    ok

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

  • COBS orbits

    ok

    Osculating elements and photometric parameters (H0, n) for active comets.

Name history

  • C/2023 H5 (Lemmon)

    Informal: Lemmon

    C/2023 H5 · 2026-09-13 22:21:23 UTC → current

Discoverers

  • Lemmon

    Discoverer · parsed-name · 2026-09-13 22:21:23 UTC → current

Contributors

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