When is the best time to observe AD Ceti?

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

Where is AD Ceti located in the sky?

AD Ceti lies in the constellation Cetus at right ascension 00h 14m and declination -07° 47′.

What telescope do I need to split AD Ceti?

Splitting AD Ceti requires an aperture of roughly 450 mm or larger — the components are separated by about 2.8″ at magnitudes near 5.1. The companion is about 6.3 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

AD Ceti — Double Star in Cetus

DoubleStar Cetus (Cet) Visible

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Observe

1Physical Properties

Magnitude 5.12

Range 4.90 - 5.16

Variable Type Semi-Regular Variable

Spectral Type M3+III

Star Color Red (B-V 1.62)

Distance 1,087 ly

2Position & Identifiers

RA 00h 14m 27.6s

Dec -07° 46' 50.0"

Constellation Cetus (Cet)

HR 46

HIP 1158

HD 1014

Variable ID AD Cet

Double Cat 180

SIMBAD

3How easy to split?

Primary 5.1 mag Companion 11.4 mag Separation 2.8″

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

Easy Medium Hard Very hard Impossible

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

To reach "Medium" at Bortle 3, you'd need at least a 450 mm reflector.

4Visibility

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Best season Aug – Oct (peak: Sep)

5Multiple Star System

Separation 2.8″

Companion Mag 11.4

Position Angle 2°

Star Colors A: Red

Discoverer BU 486

Notes

CPM.

Separation over time

Measured 1878 → 2015 (137 y)

Separation drift 3.1" → 2.8" (-0.30")

Rate -0.0022" / y

PA drift 5° → 2° (-3°, -0.022°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

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.