When is the best time to observe Chi Eridani?

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

Where is Chi Eridani located in the sky?

Chi Eridani lies in the constellation Eridanus at right ascension 01h 56m and declination -51° 37′.

What telescope do I need to split Chi Eridani?

Splitting Chi Eridani requires an aperture of roughly 650 mm or larger — the components are separated by about 2.6″ at magnitudes near 3.7. The companion is about 7.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Chi Eridani — Double Star in Eridanus

Magnitude 3.7^m DoubleStar Eridanus (Eri) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 3.70

Spectral Type G8IV subgiant

Star Color Orange (B-V 0.85)

Distance 56 ly

2Position & Identifiers

RA 01h 55m 57.5s

Dec -51° 36' 32.0"

Constellation Eridanus (Eri)

HR 566

HIP 9007

HD 11937

SAO 232573

Bayer Chi

SIMBAD

3How easy to split?

Primary 3.7 mag Companion 10.7 mag Separation 2.6″

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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 650 mm reflector.

4Visibility

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Best season Sep – Nov (peak: Oct)

5Multiple Star System

Separation 2.6″

Companion Mag 10.7

Position Angle 208°

Star Colors A: Orange

Discoverer HJ 3473

Notes

CPM.

Separation over time

Measured 1834 → 2015 (181 y)

Separation drift 12.0" → 2.6" (-9.40")

Rate -0.0519" / y

PA drift 192° → 208° (+16°, +0.088°/y)

Apparent motion is significant on a human timescale — worth revisiting in a decade.

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.