When is the best time to observe AB Ceti?

AB Ceti is best observed from September through November, with peak visibility during October when it transits around midnight in the Northern Hemisphere.

Where is AB Ceti located in the sky?

AB Ceti lies in the constellation Cetus at right ascension 02h 26m and declination -15° 20′.

What telescope do I need to split AB Ceti?

Splitting AB Ceti requires an aperture of roughly 60 mm or larger — the components are separated by about 12.2″ at magnitudes near 5.8. The companion is about 3.3 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

AB Ceti — Double Star in Cetus

DoubleStar Cetus (Cet) Visible

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Observe

1Physical Properties

Magnitude 5.83

Range 5.71 - 5.88

Period 3.0 days

Variable Type ACV:

Spectral Type A6VpSrCr

Star Color Yellow-white (B-V 0.15)

Distance 217 ly

2Position & Identifiers

RA 02h 26m 00.3s

Dec -15° 20' 28.0"

Constellation Cetus (Cet)

HR 710

HIP 11348

HD 15144

Variable ID AB Cet

Double Cat 1849

SIMBAD

3How easy to split?

Primary 5.8 mag Companion 9.1 mag Separation 12.2″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Medium+	Medium+
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) C8 203mm	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Sep – Nov (peak: Oct)

5Light Curve

6Multiple Star System Triple

Components 3 (triple)

Component IDs AB

Separation 12.2″

Companion Mag 9.1

Position Angle 297°

Star Colors A: Yellow-white B: Yellow

Discoverer H 3 80

Notes

AB CPM.

Separation over time

Measured 1782 → 2024 (242 y)

Separation drift 11.3" → 12.2" (+0.90")

Rate +0.0037" / y

PA drift 292° → 297° (+5°, +0.021°/y)

Slow change over generations — observable in lifetime comparisons.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.