When is the best time to observe 39 Eridani?

39 Eridani is best observed from October through December, with peak visibility during November when it transits around midnight in the Northern Hemisphere.

Where is 39 Eridani located in the sky?

39 Eridani lies in the constellation Eridanus at right ascension 04h 14m and declination -10° 15′.

What telescope do I need to split 39 Eridani?

Splitting 39 Eridani requires an aperture of roughly 80 mm or larger — the components are separated by about 6.7″ at magnitudes near 4.9. The companion is about 3.7 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

39 Eridani — Double Star in Eridanus

Observable Double Star Excellent (61/100)

Sep: 6.7", Companion: mag 8.5

Magnitude 4.9^m DoubleStar Eridanus (Eri) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.87

Spectral Type K3III giant

Star Color Red (B-V 1.17)

Distance 217 ly

2Position & Identifiers

RA 04h 14m 23.7s

Dec -10° 15' 23.0"

Constellation Eridanus (Eri)

HR 1318

HIP 19777

HD 26846

SAO 149478

Flamsteed 39 Eri

Double Cat 3079

SIMBAD

3How easy to split?

Primary 4.9 mag Companion 8.5 mag Separation 6.7″

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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 Oct – Dec (peak: Nov)

5Multiple Star System Triple C: optical

Components 3 (triple)

Component IDs AB

Separation 6.7″

Companion Mag 8.5

Companion Sp G2V

Position Angle 143°

Star Colors A: Red B: Yellow

Discoverer STF 516

Notes

AB binary, B is G2V.

Separation over time

Measured 1831 → 2021 (190 y)

Separation drift 8.0" → 6.7" (-1.30")

Rate -0.0068" / y

PA drift 154° → 143° (-11°, -0.058°/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.