When is the best time to observe Epsilon Trianguli?

Epsilon Trianguli is best observed from September through November, with peak visibility during October when it transits around midnight in the Northern Hemisphere.

Where is Epsilon Trianguli located in the sky?

Epsilon Trianguli lies in the constellation Triangulum at right ascension 02h 03m and declination +33° 17′.

What telescope do I need to split Epsilon Trianguli?

Splitting Epsilon Trianguli requires an aperture of roughly 250 mm or larger — the components are separated by about 4.4″ at magnitudes near 5.5. The companion is about 5.9 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Epsilon Trianguli — Double Star in Triangulum

Magnitude 4.5–6.0^m DoubleStar Triangulum (Tri) Visible

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Observe

1Physical Properties

Magnitude 5.50

Spectral Type A2V

Star Color White (B-V 0.03)

Distance 326 ly

2Position & Identifiers

RA 02h 02m 58.0s

Dec +33° 17' 02.0"

Constellation Triangulum (Tri)

HR 599

HIP 9570

HD 12471

SAO 55218

Bayer Epsilon

Flamsteed 3 Tri

Double Cat 1621

SIMBAD

3How easy to split?

Primary 5.5 mag Companion 11.4 mag Separation 4.4″

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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	Hard+	Hard+	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 250 mm reflector.

4Visibility

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Best season Sep – Nov (peak: Oct)

5Multiple Star System

Separation 4.4″

Companion Mag 11.4

Position Angle 120°

Star Colors A: White

Discoverer STF 201

Separation over time

Measured 1827 → 2016 (189 y)

Separation drift 3.0" → 4.4" (+1.40")

Rate +0.0074" / y

PA drift 100° → 120° (+20°, +0.106°/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.