When is the best time to observe Theta Persei?

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

Where is Theta Persei located in the sky?

Theta Persei lies in the constellation Perseus at right ascension 02h 44m and declination +49° 14′.

What telescope do I need to split Theta Persei?

Splitting Theta Persei requires an aperture of roughly 60 mm or larger — the components are separated by about 21.2″ at magnitudes near 4.1. The companion is about 5.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Persei — Double Star in Perseus

Magnitude 4.1^m DoubleStar Perseus (Per) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.12

Spectral Type F8V

Star Color Yellow (B-V 0.49)

Distance 42 ly

2Position & Identifiers

RA 02h 44m 12.0s

Dec +49° 13' 42.0"

Constellation Perseus (Per)

HR 799

HIP 12777

HD 16895

SAO 38288

Bayer Theta

Flamsteed 13 Per

Double Cat 2081

SIMBAD

3How easy to split?

Primary 4.1 mag Companion 9.1 mag Separation 21.2″

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	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

Set a location in User Settings to see visibility data.

Best season Sep – Nov (peak: Oct)

5Multiple Star System Triple C: optical

Components 3 (triple)

Component IDs AB

Separation 21.2″

Companion Mag 9.1

Companion Sp M1.5

Position Angle 305°

Star Colors A: Yellow B: Red

Discoverer STF 296

Notes

AB 4.13 F7V, 9.87 M1V, 2720y, a = 22.289". C probably optical.

Separation over time

Measured 1782 → 2023 (241 y)

Separation drift 13.5" → 21.2" (+7.70")

Rate +0.0320" / y

PA drift 290° → 305° (+15°, +0.062°/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.