When is the best time to observe Theta Gruis?

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

Where is Theta Gruis located in the sky?

Theta Gruis lies in the constellation Grus at right ascension 23h 07m and declination -43° 31′.

What telescope do I need to split Theta Gruis?

Splitting Theta Gruis requires an aperture of roughly 150 mm or larger — the components are separated by about 1.5″ at magnitudes near 4.3. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Gruis — Double Star in Grus

Observable Double Star Fair (24/100)

Sep: 1.5", Companion: mag 6.6

Magnitude 4.3^m DoubleStar Grus (Gru) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.28

Spectral Type F5mDel Del

Star Color Yellow-white (B-V 0.42)

Distance 192 ly

2Position & Identifiers

RA 23h 06m 52.8s

Dec -43° 31' 14.0"

Constellation Grus (Gru)

HR 8787

HIP 114131

HD 218227

SAO 231444

Bayer Theta

SIMBAD

3How easy to split?

Primary 4.3 mag Companion 6.6 mag Separation 1.5″

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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	Medium	Medium	Medium

Easy Medium Hard Very hard Impossible

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

4Visibility

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Best season Aug – Oct (peak: Sep)

5Multiple Star System Triple

Components 3 (triple)

Component IDs AB

Separation 1.5″

Companion Mag 6.6

Position Angle 115°

Star Colors A: Yellow-white B: Orange

Discoverer JC 20

Separation over time

Measured 1846 → 2013 (167 y)

Separation drift 3.1" → 1.5" (-1.60")

Rate -0.0096" / y

PA drift 12° → 115° (+103°, +0.617°/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.