When is the best time to observe Xi Bootis?

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

Where is Xi Bootis located in the sky?

Xi Bootis lies in the constellation Boötes at right ascension 14h 51m and declination +19° 06′.

What telescope do I need to split Xi Bootis?

Splitting Xi Bootis requires an aperture of roughly 100 mm or larger — the components are separated by about 4.7″ at magnitudes near 4.5. Larger apertures and steady seeing help resolve the pair cleanly.

Xi Bootis — Double Star in Boötes

Observable Double Star Excellent (64/100)

Sep: 4.7", Companion: mag 7.0

Magnitude 4.5–4.7^m DoubleStar Boötes (Boo) Visible

Star Map + List + Plan

About Xi Boo

Description

Xi Boötis is a colourful binary about 22.0 light-years away — a G7 V yellow primary at magnitude 4.55 paired with a K5 V orange-red companion of magnitude 7.0. They orbit each other every 152 years, currently around 5–6″ apart. Both components are young (about 200 million years), chromospherically active, and rotating fast — Xi Boo A has one of the strongest activity cycles measured for a sun-like star.

Observing Tips

A showpiece colour double for any small telescope — the yellow + orange contrast at 100× is striking and instantly memorable. Currently near maximum apparent separation, so the next two decades are an excellent observing window. Located 8° north-west of Arcturus.

History

Discovered as a binary by William Herschel in 1780. Used for over 200 years as a benchmark for stellar dynamos: Olin Wilson's 1960s–80s Mount Wilson HK survey showed Xi Boo A has a clear ~13-year activity cycle and Xi Boo B has shorter, more chaotic variations — a textbook example of how stellar activity depends on rotation rate.

Fun Facts

Xi Boo's high proper motion (0.5″/yr) carries the pair noticeably across the sky on multi-decade timescales. The system was a candidate target in early SETI listings because of its sun-like primary and proximity, although the youth of the system makes hosted life less likely.

Observe

1Physical Properties

Magnitude 4.55

Range 4.52 - 4.67

Period 10.1 days

Variable Type BY Draconis (Spotted Rotating)

Spectral Type G8Ve+K4Ve

Star Color Orange (B-V 0.76)

Distance 21 ly

2Position & Identifiers

RA 14h 51m 23.3s

Dec +19° 06' 04.0"

Constellation Boötes (Boo)

HR 5544

HIP 72659

HD 131156

SAO 101250

Bayer Xi

Flamsteed 37 Boo

Variable ID Xi Boo

Double Cat 9413

SIMBAD

3How easy to split?

Primary 4.6 mag Companion 7.0 mag Separation 4.7″

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Medium+	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 Mar – May (peak: Apr)

5Light Curve

6Multiple Star System Quadruple C,D,E,F: optical

Components 4 (quadruple)

Component IDs AB

Separation 4.7″

Companion Mag 7.0

Companion Sp K5V

Position Angle 292°

Star Colors A: Orange B: Red

Discoverer STF1888

Notes

AB 4.74 G8V, 6.9 K4V, 151.505y, a = 4.904". Combined mag., colors. Masses 0.89 and 0.74 solar. Perturbation period | 2.2y, a = 0.020" suspected; unresolved by speckle interferometry. Component C optical.