C/2015 D4
C/2015 D4 (Borisov)
Not currently visible. Last report 4224 days ago at mag 33.6. Historic peak was mag 12.2. Typical backyard telescopes will not show it. HST, JWST, or an 8–10 m class telescope might recover it with a good ephemeris.
Right ascension
—
J2000
Declination
—
J2000
Estimated magnitude
33.6
Professional survey · COBS consensus
Confidence
33
Class E · priority 60
Observations
1
Arc unknown
Last observation
4224d ago
Mon, 23 Feb 2015 02:52:48 GMT · COBS consensus
Perihelion
2014-10-26
0.880 au
Peak window
2014-10-21 → 2014-10-29
COBS peak mag 12.2 on 2014-10-24 · perihelion 2014-10-26. Window is those dates ±3 days — not a light-curve fit.
Historic peak
12.2
COBS / analyzed peak 2014-10-24
Catalog ingest
15h ago
Venator last wrote this row 2026-09-16 13:20:17 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.
No tail measures stored yet for this object.
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
0.880 au
e
0.9890
i
77.30°
Ω
306.00°
ω
315.00°
a
—
MOID
—
H
—
H0 / n
—
NEO score
—
PHA score
—
RMS
—
Elongation
—
Reporting sources
COBS comet list
okComet Observation Database magnitudes and perihelion data for the full COBS list (active and inactive).
Name history
C/2015 D4 (Borisov)
Informal: Borisov
C/2015 D4 · 2026-09-14 18:27:56 UTC → current
Discoverers
Discoverer · parsed-name · 2026-09-14 18:27:56 UTC → current
Contributors
CCD Observer · PRY01 · 1 reports · last 4224d ago
Pips are observation weight on this object (log of report count). Hover for catalog-wide weight.