When is the best time to observe Delta Bootis?

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

Where is Delta Bootis located in the sky?

Delta Bootis lies in the constellation Boötes at right ascension 15h 16m and declination +33° 19′.

What telescope do I need to split Delta Bootis?

Splitting Delta Bootis requires an aperture of roughly 60 mm or larger — the components are separated by about 104.7″ at magnitudes near 3.5. The companion is about 4.4 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Delta Bootis — Double Star in Boötes

Observable Double Star Good (48/100)

Sep: 104.7", Companion: mag 7.9

Magnitude 3.5^m DoubleStar Boötes (Boo) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 3.47

Spectral Type G8IV subgiant

Star Color Orange (B-V 0.95)

Distance 122 ly

2Position & Identifiers

RA 15h 15m 30.2s

Dec +33° 18' 53.0"

Constellation Boötes (Boo)

HR 5681

HIP 74666

HD 135722

SAO 64589

Bayer Delta

Flamsteed 49 Boo

Double Cat 9559

SIMBAD

3How easy to split?

Primary 3.5 mag Companion 7.9 mag Separation 104.7″

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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

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Best season Apr – Jun (peak: May)

5Multiple Star System C: optical

Separation 104.7″

Companion Mag 7.9

Companion Sp G0V

Position Angle 78°

Star Colors A: Orange B: Yellow

Discoverer STFA 27

Notes

CPM.

Separation over time

Measured 1780 → 2023 (243 y)

Separation drift 135.0" → 104.7" (-30.30")

Rate -0.1247" / y

PA drift 84° → 78° (-6°, -0.025°/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.