When is the best time to observe Tau Aquarii?

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

Where is Tau Aquarii located in the sky?

Tau Aquarii lies in the constellation Aquarius at right ascension 22h 48m and declination -14° 03′.

What telescope do I need to split Tau Aquarii?

Splitting Tau Aquarii requires an aperture of roughly 60 mm or larger — the components are separated by about 21.0″ at magnitudes near 5.7. The companion is about 3.9 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Tau Aquarii — Double Star in Aquarius

HIP 112542; Tau1 Aquarii; 69 Aquarii

Magnitude 5.7^m DoubleStar Aquarius (Aqr) Visible

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Observe

1Physical Properties

Magnitude 5.66

Spectral Type A0V

Star Color Blue-white (B-V -0.05)

2Position & Identifiers

RA 22h 47m 42.8s

Dec -14° 03' 23.0"

Constellation Aquarius (Aqr)

HR 8673

HIP 112542

HD 215766

SAO 165298

Bayer Tau1

Flamsteed 69 Aqr

Double Cat 16268

SIMBAD Wikipedia

3How easy to split?

Primary 5.7 mag Companion 9.6 mag Separation 21.0″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Medium+	Medium+	Medium
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 Jul – Sep (peak: Aug)

5Multiple Star System Triple B: optical

Components 3 (triple)

Component IDs AB

Separation 21.0″

Companion Mag 9.6

Companion Sp A9

Position Angle 127°

Star Colors A: Blue-white B: Yellow-white

Discoverer STF2943

Notes

AB optical.

Separation over time

Measured 1782 → 2017 (235 y)

Separation drift 36.8" → 21.0" (-15.80")

Rate -0.0672" / y

PA drift 110° → 127° (+17°, +0.072°/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.