When is the best time to observe Theta Hydrae?

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

Where is Theta Hydrae located in the sky?

Theta Hydrae lies in the constellation Hydra at right ascension 09h 14m and declination +02° 19′.

What telescope do I need to split Theta Hydrae?

Splitting Theta Hydrae requires an aperture of roughly 60 mm or larger — the components are separated by about 20.6″ at magnitudes near 3.9. The companion is about 6.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Hydrae — Double Star in Hydra

Magnitude 3.9^m DoubleStar Hydra (Hya) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 3.88

Spectral Type A0V

Star Color Blue-white (B-V -0.06)

Distance 128 ly

2Position & Identifiers

RA 09h 14m 21.9s

Dec +02° 18' 51.0"

Constellation Hydra (Hya)

HR 3665

HIP 45336

HD 79469

SAO 117527

Bayer Theta

Flamsteed 22 Hya

Double Cat 7253

SIMBAD

3How easy to split?

Primary 3.9 mag Companion 9.9 mag Separation 20.6″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Medium+	Medium	Hard+
150 mm Newton 150mm Newt.	Easy	Easy	Medium+
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 Jan – Mar (peak: Feb)

5Multiple Star System Quadruple optical

Components 4 (quadruple)

Component IDs AB

Separation 20.6″

Companion Mag 9.9

Position Angle 256°

Star Colors A: Blue-white

Discoverer HJ 2489

Notes

AB optical.

Separation over time

Measured 1782 → 2022 (240 y)

Separation drift 60.0" → 20.6" (-39.40")

Rate -0.1642" / y

PA drift 165° → 256° (+91°, +0.379°/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.