When is the best time to observe Sigma Gruis?

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

Where is Sigma Gruis located in the sky?

Sigma Gruis lies in the constellation Grus at right ascension 22h 37m and declination -40° 35′.

What telescope do I need to split Sigma Gruis?

Splitting Sigma Gruis requires an aperture of roughly 210 mm or larger — the components are separated by about 2.6″ at magnitudes near 5.9. The companion is about 4.2 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Sigma Gruis — Double Star in Grus

HIP 111643; Sigma2 Gruis

Magnitude 5.9^m DoubleStar Grus (Gru) Visible

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Observe

1Physical Properties

Magnitude 5.86

Spectral Type A1V

Star Color White (B-V 0.06)

2Position & Identifiers

RA 22h 36m 58.8s

Dec -40° 35' 28.0"

Constellation Grus (Gru)

HR 8602

HIP 111643

HD 214150

SAO 231217

Bayer Sigma2

SIMBAD Wikipedia

3How easy to split?

Primary 5.9 mag Companion 10.0 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.	Hard	Hard	Hard
Celestron C8 (203 mm SCT) C8 203mm	Hard+	Hard+	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 210 mm reflector.

4Visibility

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Best season Jul – Sep (peak: Aug)

5Multiple Star System E: optical

Separation 2.6″

Companion Mag 10.0

Companion Sp A3Vn

Position Angle 267°

Star Colors A: White B: White

Discoverer BU 771

Notes

CPM.

Separation over time

Measured 1879 → 2016 (137 y)

Separation drift 1.3" → 2.6" (+1.30")

Rate +0.0095" / y

PA drift 270° → 267° (-3°, -0.022°/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.