When is the best time to observe HIP 21377?

HIP 21377 is best observed from October through December, with peak visibility during November when it transits around midnight in the Northern Hemisphere.

Where is HIP 21377 located in the sky?

HIP 21377 lies in the constellation Eridanus at right ascension 04h 35m and declination -09° 44′.

What telescope do I need to split HIP 21377?

Splitting HIP 21377 requires an aperture of roughly 60 mm or larger — the components are separated by about 12.8″ at magnitudes near 6.4. Larger apertures and steady seeing help resolve the pair cleanly.

HIP 21377 — Double Star in Eridanus

Magnitude 6.4^m DoubleStar Eridanus (Eri) Visible

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Observe

1Physical Properties

Magnitude 6.37

Spectral Type A1m

Star Color White (B-V 0.11)

2Position & Identifiers

RA 04h 35m 14.0s

Dec -09° 44' 12.0"

Constellation Eridanus (Eri)

HR 1460

HIP 21377

HD 29173

SAO 131335

Double Cat 3318

SIMBAD

3How easy to split?

Primary 6.4 mag Companion 7.6 mag Separation 12.8″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
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

Separation 12.8″

Companion Mag 7.6

Position Angle 260°

Star Colors A: White B: Yellow-white

Discoverer STF 570

Notes

CPM. Companion A7V.

Separation over time

Measured 1783 → 2018 (235 y)

Separation drift 11.9" → 12.8" (+0.90")

Rate +0.0038" / y

PA drift 254° → 260° (+6°, +0.026°/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.