When is the best time to observe Kappa Cephei?

Kappa Cephei is best observed from June through August, with peak visibility during July when it transits around midnight in the Northern Hemisphere.

Where is Kappa Cephei located in the sky?

Kappa Cephei lies in the constellation Cepheus at right ascension 20h 09m and declination +77° 43′.

What telescope do I need to split Kappa Cephei?

Splitting Kappa Cephei requires an aperture of roughly 80 mm or larger — the components are separated by about 7.3″ at magnitudes near 4.4. The companion is about 4.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Kappa Cephei — Double Star in Cepheus

Observable Double Star Excellent (65/100)

Sep: 7.3", Companion: mag 8.3

Magnitude 4.4^m DoubleStar Cepheus (Cep) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.39

Spectral Type B9III giant

Star Color Blue-white (B-V -0.05)

Distance 3,262 ly

2Position & Identifiers

RA 20h 08m 53.3s

Dec +77° 42' 41.0"

Constellation Cepheus (Cep)

HR 7750

HIP 99255

HD 192907

SAO 9665

Bayer Kappa

Flamsteed 1 Cep

Double Cat 13524

SIMBAD

3How easy to split?

Primary 4.4 mag Companion 8.3 mag Separation 7.3″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Medium	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 Jun – Aug (peak: Jul)

5Multiple Star System Triple C: optical

Components 3 (triple)

Component IDs AB

Separation 7.3″

Companion Mag 8.3

Position Angle 121°

Star Colors A: Blue-white B: Yellow

Discoverer STF2675

Separation over time

Measured 1782 → 2021 (239 y)

Separation drift 5.8" → 7.3" (+1.50")

Rate +0.0063" / y

PA drift 123° → 121° (-2°, -0.008°/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.