When is the best time to observe Tau Hydrae?

Tau Hydrae is best observed from January through March, with peak visibility during February when it transits around midnight in the Northern Hemisphere.

Where is Tau Hydrae located in the sky?

Tau Hydrae lies in the constellation Hydra at right ascension 09h 29m and declination -02° 46′.

What telescope do I need to split Tau Hydrae?

Splitting Tau Hydrae requires an aperture of roughly 60 mm or larger — the components are separated by about 65.7″ at magnitudes near 4.6. Larger apertures and steady seeing help resolve the pair cleanly.

Tau Hydrae — Double Star in Hydra

HIP 46509; Tau1 Hydrae; 31 Hydrae

Observable Double Star Good (53/100)

Sep: 65.7", Companion: mag 7.3

Magnitude 4.6^m DoubleStar Hydra (Hya) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.60

Spectral Type F6V

Star Color Yellow (B-V 0.46)

Distance 45 ly

2Position & Identifiers

RA 09h 29m 08.9s

Dec -02° 46' 08.0"

Constellation Hydra (Hya)

HR 3759

HIP 46509

HD 81997

SAO 136895

Bayer Tau1

Flamsteed 31 Hya

SIMBAD Wikipedia

3How easy to split?

Primary 4.6 mag Companion 7.3 mag Separation 65.7″

Sign in and configure your equipment and default location to see a personalized row.

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
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

Set a location in User Settings to see visibility data.

Best season Jan – Mar (peak: Feb)

5Multiple Star System

Separation 65.7″

Companion Mag 7.3

Companion Sp K0

Position Angle 4°

Star Colors A: Yellow B: Orange

Discoverer HJ 1167

Notes

CPM.

Separation over time

Measured 1782 → 2016 (234 y)

Separation drift 61.7" → 65.7" (+4.00")

Rate +0.0171" / y

PA drift 359° → 4° (+5°, +0.021°/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.