astronomy

T Coronae Borealis

T Coronae Borealis is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand T Coronae Borealis rather than just read about it. In short: T Coronae Borealis is a binary star and a recurrent nova about 3,000 light-years (920 parsecs) away in the constellation Corona Borealis. T Coronae Borealis is its variable-star designation and the name most frequently used in the astronomical literature, but it also has the official proper name Blaze Star.

Key takeaways

T Coronae Borealis belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect T Coronae Borealis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of T Coronae Borealis from memory before moving on to harder problems.

Reference excerpt

T Coronae Borealis is a binary star and a recurrent nova about 3,000 light-years (920 parsecs) away in the constellation Corona Borealis. T Coronae Borealis is its variable-star designation and the name most frequently used in the astronomical literature, but it also has the official proper name Blaze Star. The system was first observed in outburst in 1866 by John Birmingham, but had been observed earlier in quiescence as a 10th magnitude star. It may have been observed in 1217 and in 1787 as well. In February 1946, the flare-up was discovered independently by three observers: the Soviet amateur astronomer A. S. Kamenchuk, the 15-year-old schoolboy Michael Woodman from Wales, and the British variable star observer N. F. H. Knight. This led to the theory that the star flares every 80 years with the next nova expected to occur before 2027. Its apparent magnitude varies between 2.0 and 10.8, representing about a 3300-fold change in brightness. T Coronae Borealis enters solar conjunction and becomes hidden by the Sun's glare in late November.

Nomenclature T Coronae Borealis (abbreviated T CrB or unofficially T Cor Bor) is the star's variable star designation and is its most commonly used name. It also has the Bright Star Catalogue designation HR 5958 and the Henry Draper Catalogue designation HD 143454. The proper name Blaze Star has been used since its outburst in 1866, and was officially approved by the IAU Working Group on Star Names on 22 September 2025.

Description

T CrB normally has a magnitude of about 10, which is near the limit of typical binoculars. Two well-documented outbursts have been observed, reaching magnitude 2.0 on May 12, 1866 and magnitude 3.0 on February 9, 1946, though a more recent paper shows the 1866 outburst with a possible peak range of magnitude 2.5±0.5. When at peak magnitude of 2.5, this recurrent nova is dimmer than about 100 brightest stars in the night sky, but easily visible to the naked eye.

T CrB is a binary system containing a large cool component and a smaller hot component. The cool component is a red giant that transfers material to the hot component. The hot component, which initially was the most massive and brightest of the two stars, is now 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 overall luminosity of the system increases by orders of magnitude.

The two components of the system orbit each other every 227.5528 d. The orbit is almost circular and is inclined at an angle of 61.5°. The separation between the components is 0.960 AU.

2016–present activity On April 20, 2016, Sky & Telescope reported a sustained brightening since February 2015 from magnitude 10.5 to about 9.2. A similar event was reported in 1938, 8 years before the 1946 outburst. By June 2018, the star had dimmed slightly but still remained at an unusually high level of activity. By mid-2023, it had faded by 0.35 magnitude or about 28%; its lowest brightness seen since 2016. A similar dimming occurred in the year before the 1946 outburst, leading some to predict an eruption before September 2024. The eruption has repeatedly been predicted to be imminent, but no nova has been observed as of August 2026 and several predictions have already lapsed.

Outburst predictions Predictions of the next nova (in order of when the prediction was made):

Notes

References

Further reading Wallerstein, George; Tanya Harrison; Ulisse Munari; Andrew Vanture (May 11, 2008). "The Metallicity and Lithium Abundances of the Recurring Novae T CrB and RS Oph". Publications of the Astronomical Society of the Pacific. 120 (867). University of Chicago Press: 492–497. Bibcode:2008PASP..120..492W. doi:10.1086/587965. ISSN 1538-3873. OCLC 40768120. S2CID 106406607. MacRobert, Alan M. (April 6, 2012). Naeye, Robert (ed.). "R and T Coronae Borealis: Two Stellar Opposites". Sky & Telescope. Sky Publishing. ISSN 0037-6604. OCLC 1765612. Archived from the original on April 6, 2012.

External links Blaze Star, The Worlds of David Darling AAVSO: Check Recent Observations (get recent magnitude estimates for T CrB)

Illustrations

Worked examples

Example 1 — a first encounter with T Coronae Borealis

Start with the simplest possible case. Write down what T Coronae Borealis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to T Coronae Borealis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about T Coronae Borealis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of T Coronae Borealis

In research: T Coronae Borealis appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses T Coronae Borealis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: T Coronae Borealis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1866, Corona Borealis, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for T Coronae Borealis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study T Coronae Borealis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what T Coronae Borealis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain T Coronae Borealis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is T Coronae Borealis in simple terms?

Why does T Coronae Borealis matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study T Coronae Borealis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on T Coronae Borealis.