When is the best time to observe Eta Gruis?

Eta Gruis is best observed from July through September, with peak visibility during August when it transits around midnight in the Northern Hemisphere.

Where is Eta Gruis located in the sky?

Eta Gruis lies in the constellation Grus at right ascension 22h 46m and declination -53° 30′.

What telescope do I need to split Eta Gruis?

Splitting Eta Gruis requires an aperture of roughly 60 mm or larger — the components are separated by about 25.6″ at magnitudes near 4.8. The companion is about 6.7 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Eta Gruis — Double Star in Grus

Magnitude 4.8^m DoubleStar Grus (Gru) Visible

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1Physical Properties

Magnitude 4.85

Spectral Type K2IIICNIV giant

Star Color Red (B-V 1.18)

Distance 652 ly

2Position & Identifiers

RA 22h 45m 37.9s

Dec -53° 30' 01.0"

Constellation Grus (Gru)

HR 8655

HIP 112374

HD 215369

SAO 247570

Bayer Eta

SIMBAD

3How easy to split?

Primary 4.9 mag Companion 11.5 mag Separation 25.6″

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

Easy Medium Hard Very hard Impossible

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

4Visibility

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Best season Jul – Sep (peak: Aug)

5Multiple Star System

Separation 25.6″

Companion Mag 11.5

Position Angle 187°

Star Colors A: Red

Discoverer CRU 4

Separation over time

Measured 1879 → 2012 (133 y)

Separation drift 27.6" → 25.6" (-2.00")

Rate -0.0150" / y

PA drift 185° → 187° (+2°, +0.015°/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.