When is the best time to observe Zeta Aquarii?

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

Where is Zeta Aquarii located in the sky?

Zeta Aquarii lies in the constellation Aquarius at right ascension 22h 29m and declination -00° 01′.

What telescope do I need to split Zeta Aquarii?

Splitting Zeta Aquarii requires an aperture of roughly 650 mm or larger — the components are separated by about 2.5″ at magnitudes near 4.4. The companion is about 6.9 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Zeta Aquarii — Double Star in Aquarius

HIP 110960; Zeta2 Aquarii; 55 Aquarii

Magnitude 4.4^m DoubleStar Aquarius (Aqr) Visible

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Observe

1Physical Properties

Magnitude 4.42

Spectral Type F3V

Star Color Yellow-white (B-V 0.38)

Distance 148 ly

2Position & Identifiers

RA 22h 28m 50.1s

Dec -00° 01' 12.0"

Constellation Aquarius (Aqr)

HR 8559

HIP 110960

HD 213052

SAO 146108

Bayer Zeta2

Flamsteed 55 Aqr

Double Cat 15971

SIMBAD Wikipedia

3How easy to split?

Primary 4.4 mag Companion 11.3 mag Separation 2.5″

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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.	V. hard	V. hard	V. hard
Celestron C8 (203 mm SCT) C8 203mm	V. hard	V. hard	V. 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 650 mm reflector.

4Visibility

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Best season Jul – Sep (peak: Aug)

5Multiple Star System Triple

Components 3 (triple)

Separation 2.5″

Companion Mag 11.3

Position Angle 154°

Star Colors A: Yellow-white

Notes

Binary with HR 8558. AB 4.31 F2IV, 4.51 F3IV, 856.0y, a = 5.055". Magnitude for blend 3.65V, combined colors. | Component B, HR 8558, is an astrometric binary.