When is the best time to observe Theta Bootis?

Theta Bootis is best observed from March through May, with peak visibility during April when it transits around midnight in the Northern Hemisphere.

Where is Theta Bootis located in the sky?

Theta Bootis lies in the constellation Boötes at right ascension 14h 25m and declination +51° 51′.

What telescope do I need to split Theta Bootis?

Splitting Theta Bootis requires an aperture of roughly 60 mm or larger — the components are separated by about 69.4″ at magnitudes near 4.0. The companion is about 7.4 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Bootis — Double Star in Boötes

Magnitude 4.0^m DoubleStar Boötes (Boo) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.05

Range 4.04 - 4.06

Period 2.9 days

Variable Type ROT

Spectral Type F7V

Star Color Yellow (B-V 0.50)

Distance 45 ly

2Position & Identifiers

RA 14h 25m 11.8s

Dec +51° 51' 03.0"

Constellation Boötes (Boo)

HR 5404

HIP 70497

HD 126660

SAO 29137

Bayer Theta

Flamsteed 23 Boo

SIMBAD

3How easy to split?

Primary 4.1 mag Companion 11.5 mag Separation 69.4″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Hard	Hard	V. hard+
150 mm Newton 150mm Newt.	Medium+	Medium	Hard+
Celestron C8 (203 mm SCT) C8 203mm	Medium+	Medium+	Medium

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Mar – May (peak: Apr)

5Light Curve

6Multiple Star System

Separation 69.4″

Companion Mag 11.5

Companion Sp M2.5V

Position Angle 182°

Star Colors A: Yellow B: Red

Discoverer STT 580

Notes

CPM.

Separation over time

Measured 1854 → 2023 (169 y)

Separation drift 69.1" → 69.4" (+0.30")

Rate +0.0018" / y

PA drift 182° → 182° (+0°, +0.000°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

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.