IAU Constellation (CrB) · Genitive: Coronae Borealis · Northern Sky

Corona Borealis (Northern Crown) Guide

Corona Borealis IAU constellation (179 sq deg, rank 73): July semicircular crown between Boötes and Hercules, led by Alphecca (+2.23) and T CrB.

Solid-Angle Area179 sq deg (Rank #73 of 88)
Best Evening MonthJuly
Visibility Latitudes+90° to −50°
Brightest StarAlphecca (Alpha Coronae Borealis) (+2.23)

Sky Navigation & Astrophysical Context

Nestled between the Herdsman Boötes to the west and the Keystone of Hercules to the east, Corona Borealis covers 179 square degrees of the northern summer sky. Its seven main stars—Theta, Beta (Nusakan), Alpha (Alphecca/Gemma), Gamma, Delta, Epsilon, and Iota Coronae Borealis—form one of the most convincing and compact C-shaped diadem arcs in the heavens, associated in Greek myth with the jewel-studded crown presented by Dionysus to Ariadne.

The central jewel of the Crown is Alphecca (Alpha Coronae Borealis, also called Gemma, V = +2.23), an A0 V + G5 V eclipsing binary at 23 parsecs that belongs to the coeval Ursa Major Moving Group and dips slightly by 0.11 magnitudes every 17.36 days when the solar-type companion transits the primary.

Corona Borealis is a famous laboratory for stellar variability: inside the bowl of the Crown sits R Coronae Borealis, the hydrogen-deficient carbon supergiant prototype that shines near magnitude +5.8 for years before unpredictably fading down to 14th magnitude as it ejects clouds of amorphous carbon soot; just 1° southeast of Epsilon CrB lies T Coronae Borealis ('The Blaze Star'), a recurrent symbiotic nova that erupts from magnitude +10.0 to naked-eye magnitude +2.0 roughly every 80 years (1866, 1946, 2020s).

Bordering IAU Constellations: Boötes, Hercules, Serpens Caput.

Equatorial Center Position & Transit Altitude

Corona Borealis is centered near Right Ascension 15h 50m 24s, Declination +32° 37′ 12″ (The Northern Crown).

J2000 Equatorial Sky Position (Corona Borealis) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 83° 40°N Lat 27° 30°S Lat RA: 15h 50m 24s Dec: +32° 37′ 12″ Epoch: J2000.0 · 179 sq deg (Rank #73) First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Practical Star-Hopping & Observing Tips

  • Locate the C-shaped arc of Corona Borealis one-third of the way along a line from orange Arcturus toward Vega.
  • Check R Coronae Borealis (inside the bowl between Alpha and Iota CrB) with 10×50 binoculars to see whether it is at its normal +5.8 plateau or in a carbon-dust fade.
  • Monitor the position 1° southeast of Epsilon Coronae Borealis for the recurrent nova T Coronae Borealis ('The Blaze Star').

Notable Celestial Objects in & Near Corona Borealis

Cataloged Stars and Deep-Sky Objects Associated with Corona Borealis
ObjectFamilyClassificationRA (J2000)Dec (J2000)Min. Instrument
Arcturus (Alpha Bootis Red Giant)starsK-type red giant branch star (thick-disk / Arcturus stream)14h 15m 39.67s+19° 10′ 56.7″Naked eye
Messier 13 (Hercules Globular Cluster)globular-clustersGlobular cluster16h 41m 41.24s+36° 27′ 35.5″7×50 binoculars (naked eye under dark skies)
R Coronae Borealis (Reverse Nova Carbon Star)variable-starsPrototype hydrogen-deficient carbon-rich supergiant ('reverse nova' variable)15h 48m 34.41s+28° 26′ 45.3″7×50 binoculars at maximum (mag 5.8); 250–350 mm telescope at deep minimum (mag 14–15)
T Coronae Borealis (The Blaze Star Nova)variable-starsSymbiotic recurrent nova binary (massive accreting white dwarf + M4 III red giant)15h 59m 30.16s+25° 55′ 12.6″60 mm telescope / 15×70 binoculars in quiescence (mag 10.0); naked eye in outburst (mag 2.0)

Scientific Sources Cited