Epoch J2000 Equinox J2000
|Right ascension||15h 59m 30.1622s|
|Declination||25° 55′ 12.613″|
|Apparent magnitude (V)||2.0–10.8|
|Evolutionary stage||Red giant + white dwarf|
|Variable type||recurrent nova|
|Radial velocity (Rv)||−27.79 km/s|
|Proper motion (μ)|| RA: −4.220 mas/yr |
Dec.: 12.364 mas/yr
|Parallax (π)||1.2127 ± 0.0488 mas|
|Period (P)||227.8 d|
|Semi-major axis (a)||0.54 AU|
|Surface gravity (log g)||2.0 cgs|
T Coronae Borealis (T CrB), is a recurring nova in the constellation Corona Borealis. It was first discovered in outburst in 1866 by John Birmingham, although it had been observed earlier as a 10th magnitude star.
T CrB normally has a magnitude of about 10, which is near the limit of typical binoculars. It has been seen to outburst twice, reaching magnitude 2.0 on May 12, 1866 and magnitude 3.0 on February 9, 1946, although a more recent paper shows the 1866 outburst with a possible peak range of magnitude 2.5 ± 0.5. Even when at peak magnitude of 2.5, this recurrent nova is dimmer than about 120 stars in the night sky. It is sometimes nicknamed the Blaze Star.
T CrB is a binary system containing a large cool component and a smaller hot component. The cool component is a red giant which is transferring material to the hot component. The hot component is a white dwarf surrounded by an accretion disc, all hidden inside a dense cloud of material from the red giant. When the system is quiescent, the red giant dominates the visible light output and the system appears as an M3 giant. The hot component contributes some emission and dominates the ultraviolet output. During outbursts, the transfer of material to the hot component increases greatly, the hot component expands, and the luminosity of the system increases. 
The two components of the system orbit each other every 228 days. The orbit is almost circular and is inclined at an angle of 67°. The stars are separated by 0.54 AU.
On 20 April 2016, the Sky and Telescope website reported a sustained brightening since February 2015 from magnitude 10.5 to about 9.2. A similar event was reported in 1938, shortly before the 1946 outburst. By June 2018, the star had dimmed slightly but still remained at an unusually high level of activity. Since then, according to observations sent to the AAVSO, the star has hovered around magnitude 10.0.