Variable Stars · Constellation Corona Borealis

R Coronae Borealis (HD 141527)

Coordinates, Gaia DR3 distance (1.30 kpc), hydrogen-deficient carbon supergiant, 9-magnitude soot-cloud fade-outs, and observing guide for R CrB.

Right Ascension (J2000.0)15h 48m 34.41s
Declination (J2000.0)+28° 26′ 45.3″
Primary ClassificationPrototype hydrogen-deficient carbon-rich supergiant ('reverse nova' variable)
Best Observing SeasonSpring to Summer (April–September)

Provenance-Backed Scientific Measurements

Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.

Astrometric, Photometric, and Physical Parameters for R Coronae Borealis (HD 141527)
ParameterValueUncertaintyMethod & EpochQuality StatusSource Archive
Quiescent maximum visual magnitude (V)5.85 mag± 0.15 magAAVSO V-band monitoring (plummets unpredictably from 5.71 down to 15.2 during soot eclipses!)definitiveSIMBAD Astronomical Database (CDS)
Trigonometric distance (Gaia DR3)1300 pc± 45 pcGaia DR3 astrometric parallax (0.768 ± 0.026 mas / 4,240 ± 150 ly) (J2016.0)definitiveESA Gaia Archive — Data Release 3
Bolometric luminosity10000 L☉± 1500 L☉Optical + mid-IR dust shell SED integration at 1.30 kpchigh-confidenceSIMBAD Astronomical Database (CDS)
Photospheric radius75 R☉± 10 R☉Derived from L ≈ 10,000 L☉ and Teff = 6,750 ± 250 Kmodel-dependentSIMBAD Astronomical Database (CDS)
Measurement Uncertainties & Competing Solutions: While Gaia DR3 resolves R Coronae Borealis's long-uncertain distance to 1,300 ± 45 pc (4,240 ly), its circumstellar dust puffs are ejected in random directions—only those puffs launched directly along Earth's line of sight trigger deep optical fade-outs.

J2000 Equatorial Sky Chart & Culmination Altitude

The chart below plots R Coronae Borealis (Reverse Nova Carbon Star) at RA 15h 48m 34.41s, Dec +28° 26′ 45.3″ within Corona Borealis, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.

J2000 Equatorial Sky Position (Corona Borealis) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 78° 40°N Lat 32° 30°S Lat RA: 15h 48m 34.41s Dec: +28° 26′ 45.3″ Epoch: J2000.0 · V = 5.85 mag First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Astrophysical Context & Structure

R Coronae Borealis (R CrB, HD 141527), discovered as a variable star by English astronomer Edward Pigott in 1795 inside the bowl of the Northern Crown, is the archetype of the 'reverse novae' (RCB variables). Whereas a classical nova spends years in obscurity before suddenly erupting in brightness, R Coronae Borealis shines for years at a steady naked-eye/binocular maximum around magnitude 5.8, only to plummet without warning over a few weeks by up to 9 magnitudes—a factor of 4,000 drop in visible light down to magnitude 14.8–15.2! Its historic 2007–2016 minimum kept the star faint for nearly a decade.

Spectroscopy reveals why R Coronae Borealis behaves this way: located 1,300 ± 45 parsecs (4,240 light-years) away, it is a rare, ultra-evolved yellow supergiant (6,750 K, ~0.8 solar masses, ~75 solar radii) whose atmosphere is 98% helium and ~1% carbon with almost zero hydrogen (less than 1 part in 100,000). Enriched in the uncommon oxygen isotope ¹⁸O, R CrB stars are believed to be the product of the merger of two white dwarfs (a carbon-oxygen white dwarf and a helium white dwarf) that reignited helium shell burning.

Every few years, convective pulsations lift a plume of carbon-rich gas to ~2 stellar radii above the photosphere where it cools below 1,500 K and condenses into an opaque cloud of amorphous carbon soot. When a soot cloud forms directly along our line of sight, it blots out the star in visible light like a natural coronagraph while glowing brightly in the infrared until radiation pressure blows the dust away.

Practical Visual Observing Guide

Minimum Instrument7×50 binoculars at maximum (mag 5.8); 250–350 mm telescope at deep minimum (mag 14–15)
Recommended Magnification7×–10× binoculars at maximum; 150×–250× at minimum
Best Evening SeasonSpring to Summer (April–September)
  • Situated right inside the U-shaped bowl of Corona Borealis (about 2° northeast of Alphecca / α CrB), R CrB is one of the most thrilling targets in amateur astronomy: check it with 7×50 or 10×50 binoculars every clear night!
  • When at maximum (~5.8 mag), R CrB is immediately obvious in binoculars inside the Crown; if you look into the Crown and R CrB has vanished from your binoculars, a carbon-soot eclipse is underway and you will need a 200–350 mm telescope to spot it at minimum.

Catalog Cross-Identifications & Aliases

Common Aliases: R CrB · HD 141527 · HIP 77442 · HR 5880

Cross-Catalog Identifiers for R Coronae Borealis (HD 141527)
Catalog AuthorityIdentifier
GAIADR31220266466159164544
HIPHIP 77442
HDHD 141527
SIMBADV* R CrB
WIKIDATAQ1334436
Related Object · Corona Borealis

T Coronae Borealis (The Blaze Star Nova)

Coordinates, Gaia DR3 distance (916 pc), 227.57-day symbiotic M4 III + 1.37-M☉ white dwarf orbit, 80-year recurrent nova cycle, and guide for T CrB.

Related Object · Cetus

Mira (Omicron Ceti Pulsating Giant)

Coordinates, Hipparcos distance (100 pc), 332-day pulsation cycle (mag 2.0 to 10.1), white dwarf companion, and observing guide for Mira.

Reference Guide

Apparent vs Absolute Magnitude Explained

Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.

Reference Guide

Stellar Spectral Classification (OBAFGKM)

Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.

Scientific Sources & Dataset Provenance