When is the best time to observe Theta Coronae Borealis?

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

Where is Theta Coronae Borealis located in the sky?

Theta Coronae Borealis lies in the constellation Corona Borealis at right ascension 15h 33m and declination +31° 22′.

What telescope do I need to split Theta Coronae Borealis?

Splitting Theta Coronae Borealis requires an aperture of roughly 280 mm or larger — the components are separated by about 0.8″ at magnitudes near 4.1. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Coronae Borealis — Double Star in Corona Borealis

Magnitude 4.1–4.3^m DoubleStar Corona Borealis (CrB) Visible

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Observe

1Physical Properties

Magnitude 4.14

Range 4.06 - 4.33

Variable Type BE

Spectral Type B6Vnne

Star Color Blue-white (B-V -0.13)

Distance 121 ly

2Position & Identifiers

RA 15h 32m 55.8s

Dec +31° 21' 33.0"

Constellation Corona Borealis (CrB)

HR 5778

HIP 76127

HD 138749

SAO 64769

Bayer Theta

Flamsteed 4 CrB

SIMBAD

3How easy to split?

Primary 4.1 mag Companion 6.3 mag Separation 0.9″

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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 280 mm reflector.

4Visibility

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Best season Apr – Jun (peak: May)

5Multiple Star System

Separation 0.8″

Companion Mag 6.3

Position Angle 198°

Star Colors A: Blue-white B: Yellow-white

Discoverer COU 610

Separation over time

Period: 361.1 y Eccentricity: 0.780 Now: 0.85", PA 197° + 0.00" in 5 years

Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.

Eyepiece View

Telescope Eyepiece

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80x Dawes: 1.9″ TFOV: 0.6°

Seeing

Scale Realistic = true angular size

A: 4.1 · B: 6.3 · Sep: 0.8″ · PA: 198° · N up, E right

Unresolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″

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Size Comparison

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Compare Stars

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Spectral Classification

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Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map

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Stellar Lifecycle

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Blackbody Spectrum

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Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

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Stellar Fusion

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15Stellar Notes

Variable Star

Component A is NSV 7134, 4.12V, amp. 0.7m. However, 1300 UBV observations on 57 nights (1984-6) revealed no variation | over 0.06 mag. R-I also found at -0.16. Component B, the rarely seen companion, is NSV 7135, 5.5, 7.8v.

Group/Cluster

Member of the local association (Pleiades group).

Radial Velocity

Primary probably not variable and velocity probably constant.

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