Eruption Status Explained
This page tracks the status of T Coronae Borealis (T CrB), the recurrent nova known as the Blaze Star, which astronomers predict will erupt in 2026. When the eruption occurs, T CrB will brighten from magnitude +10.2 (visible only in telescopes) to magnitude +2 (visible to the naked eye) within a few hours — a 1,500-fold increase in brightness.
Subscribe for eruption alerts
Bookmark this page and check back weekly. When the eruption begins, the status banner at the top will change within 24 hours. For real-time alerts, visit the AAVSO website and create an account to receive email or SMS notifications when T CrB's magnitude changes significantly. The AAVSO's automated alert system is the fastest way to learn about the eruption — it typically triggers within minutes of a confirmed magnitude change reported by an experienced observer.
Currently: Quiescent (Pre-Eruption)
Currently: Quiescent (Pre-Eruption)
- T CrB is faint at magnitude +10.2 — requires a 4-inch telescope or larger to see
- The star follows a predictable pre-eruption pattern with small brightness fluctuations
- A "pre-eruption dip" (a slight dimming) has been observed, consistent with the 1946 pattern
- Professional and amateur astronomers monitor it daily via the AAVSO network
- When the nova begins, the star will brighten detectably within hours
When Eruption Happens: What to Expect
- The "Eruption Status" banner at the top of this page will switch from yellow to green
- A detailed eruption report with magnitude, time, and visual description will appear below
- T CrB will become visible to the naked eye in Corona Borealis within hours of eruption onset
- The nova will remain visible to the naked eye for several days, then fade over weeks
- Binoculars and small telescopes will show it easily throughout the eruption period
Understanding T CrB: The Blaze Star Binary System
T Coronae Borealis is a symbiotic binary star system — a rare pairing of two very different stars that interact through mass transfer. The primary star is a white dwarf, the Earth-sized remnant of a Sun-like star that has exhausted its nuclear fuel and collapsed to an incredibly dense state. A single teaspoon of white dwarf material weighs about 15 tons. The white dwarf in T CrB is estimated to have a mass of about 1.37 solar masses — critically close to the Chandrasekhar limit of 1.44 solar masses, beyond which it would collapse into a neutron star or trigger a Type Ia supernova.
The companion star is a red giant — a swollen, cool star that has expanded to many times its original diameter as it nears the end of its life. The red giant in T CrB is losing mass at a steady rate through its outer atmosphere, which spills onto the white dwarf via an accretion disk. This mass transfer has been ongoing for thousands of years, and the resulting accumulation on the white dwarf's surface is what triggers the recurrent nova eruptions approximately every 80 years.
The binary nature of T CrB was first deduced from its spectrum, which shows features characteristic of both a hot (white dwarf) and cool (red giant) star. The two stars orbit each other every 228 days at a distance comparable to the Earth-Sun distance. This close orbit means the red giant's outer atmosphere is constantly being stripped by the white dwarf's powerful gravity — a process that accelerates as the white dwarf grows more massive over time. Eventually, in millions of years, the white dwarf may reach the Chandrasekhar limit and explode as a Type Ia supernova, but for now, the system produces spectacular but survivable nova outbursts instead.
Why T CrB's eruptions are predictable
The 80-year cycle of T CrB is determined by the mass transfer rate and the critical pressure needed to ignite hydrogen fusion on the white dwarf's surface. Think of it like a pressure cooker: the white dwarf's extreme gravity compresses the infalling hydrogen until the base of the accumulated layer reaches approximately 20 million Kelvin. At this temperature, hydrogen fusion ignites in a runaway reaction — a titanic thermonuclear explosion that blasts the accumulated material into space at thousands of kilometres per second. The 1946 eruption ejected material equivalent to about 10 Earth masses. After the explosion, the mass transfer resumes, and the 80-year countdown begins anew.
Current Magnitude and Comparison Stars
The chart below shows the current brightness of T CrB compared to reference stars of known magnitude in the Corona Borealis region. Use these comparison stars to estimate T CrB's brightness visually through your telescope — this is the same method used by professional variable star observers.
| Star | Magnitude (V) | Status |
|---|---|---|
| Alphacca (α CrB) | 2.2 | Naked-eye reference — 10,000× brighter than T CrB now |
| Theta CrB | 4.1 | Naked-eye reference — useful for estimating eruption peak |
| Sigma CrB | 5.2 | Binocular limit — good for tracking fading after eruption |
| HD 143914 | 8.5 | Comparison A — visible in 50mm binoculars |
| HD 144531 | 9.2 | Comparison B — visible in small telescopes |
| T CrB (current) | +10.2 | Quiescent — 4-inch telescope minimum |
| Comparison C (TYC 2018-) | 10.5 | Fainter than T CrB — good for depth comparison |
V-magnitude values from the AAVSO comparison star sequence for T CrB. Use these to make your own visual magnitude estimates through a telescope. Report your observations to AAVSO using their web form.
Observing T CrB Tonight — Finder Guide
Corona Borealis is well-placed for evening observing from May through October 2026. The constellation culminates (reaches its highest point) around 10 PM local time in June and July, making T CrB accessible for the entire evening.
To locate T CrB, first find Corona Borealis — a distinctive U-shaped arc of stars between Boötes (with bright Arcturus) and Hercules. The brightest star in Corona Borealis is Alphacca (α CrB, magnitude 2.2), which marks the crown's brightest jewel. T CrB is located approximately 1 degree south of Epsilon CrB (ε CrB, magnitude 4.1) — about the width of a pinky finger at arm's length. Through a 4-inch or larger telescope at 50–60×, T CrB appears as a faint star slightly dimmer than its nearest comparison stars.
For a detailed finder chart with star-hopping instructions from Alphacca, telescope recommendations, and binocular settings, see our complete T CrB guide with finder chart.
Tonight's observing window (example)
For mid-northern latitudes (40°N) on July 1, 2026: Corona Borealis rises by 9 PM local time and is well-placed for observing from 10 PM through 2 AM. The constellation reaches an altitude of 60° above the southern horizon at culmination — comfortable for all telescope types including Dobsonians. Moon phase is critical — check a lunar calendar to pick a night within a few days of New Moon for the deepest view of T CrB's current magnitude.
Eruption History and Pattern
T CrB has been observed erupting in 1866, 1946, and (predicted) 2026. The pattern between the first two eruptions was remarkably consistent, giving astronomers confidence in the 2026 prediction.
| Date | Peak Magnitude | Duration at Peak | Observer |
|---|---|---|---|
| May 12, 1866 | +2.0 | ~3 days | John Birmingham (Ireland) |
| February 9, 1946 | +2.5 | ~2 days | Multiple observers worldwide |
| Predicted 2026 | ~+2 (expected) | ~2–3 days (est.) | Global AAVSO network |
In both 1866 and 1946, T CrB faded from peak brightness over approximately 3–5 months, with some brightness oscillations during the decline. Observers with binoculars can track the fading phase for weeks after the naked-eye visibility ends.
What Will Happen When T CrB Erupts — A Timeline
When T CrB begins its eruption, the sequence of events follows a well-documented pattern based on the 1866 and 1946 eruptions. Here is what astronomers expect will happen, hour by hour:
Trigger event — the eruption begins
The first sign of eruption is a rapid, continuous brightening of T CrB over approximately 2 hours. The star rises from magnitude +10.2 through magnitude +8, then +6 — faster than any known variable star phenomenon except for cataclysmic variables. The AAVSO alert system will trigger when the magnitude crosses the +9 threshold, sending notifications to thousands of observers worldwide. This is the moment to grab your binoculars and head outside.
Peak brightness reached
Within 4–6 hours of the trigger, T CrB reaches magnitude +2 to +2.5 — comparable to Polaris (the North Star). At this brightness, the nova is easily visible to the naked eye even from suburban skies. The star will appear as a distinct orange-red point of light in Corona Borealis, noticeably warmer in colour than the white-blue stars of Vega and Altair nearby. Through binoculars, the colour contrast is striking — T CrB appears as a vivid orange star against the more neutral white of its neighbours.
First night of naked-eye visibility
The nova remains at or near peak brightness for approximately 24–48 hours. This is the prime observing window for most people. The star may fluctuate slightly in brightness (by 0.1–0.3 magnitudes) during this period. Sketch the position of T CrB relative to Alphacca and the Corona Borealis arc — your drawings will be historically valuable for documenting the eruption's visual appearance.
Fading begins — steady decline
After 2–3 days at peak, T CrB begins a steady, gradual decline of approximately 0.1 magnitudes per day. The star remains visible to the naked eye for about 7–10 days after eruption, fading from magnitude +2 to +4. During this period, binoculars become increasingly useful, and the star's colour may shift slightly as different emission lines dominate the spectrum. The star may show small "bumps" in its light curve — brief brightenings of 0.2–0.5 magnitudes — as it fades.
Late-stage fading — telescope only
After approximately one month, T CrB fades below naked-eye visibility (magnitude +5 and dimmer). Small telescopes (4–6 inch) continue to show it clearly as a faint star. The decline continues for 3–5 months total before T CrB returns to its quiescent magnitude of +10.2. The exact shape of the light curve — how fast it fades and whether it shows oscillations — depends on the amount of material ejected and the structure of the white dwarf's accretion disk.
The 1866 and 1946 Eruptions — Historical Observations
The first recorded eruption of T CrB was discovered on May 12, 1866, by Irish astronomer John Birmingham, observing from his private observatory in Millbrook, County Mayo. Birmingham noticed a star of magnitude 2.0 in Corona Borealis where no star had been visible before — the quiescent T CrB at magnitude +10 was too faint for his 4.5-inch telescope to detect. He immediately reported his observation to the Royal Astronomical Society. The nova remained at peak brightness for approximately three days before beginning its decline. British astronomer William Huggins, a pioneer of stellar spectroscopy, studied the 1866 eruption with his spectroscope — one of the first spectroscopic analyses of a nova. He identified bright emission lines of hydrogen (particularly H-alpha) superimposed on a continuous spectrum, confirming the eruption involved hot, fast-moving gas. Birmingham died in 1884, never knowing the star he discovered would erupt again 80 years later and become one of the most important recurrent novae in astronomy.
The 1946 eruption was detected on February 9 by multiple observers simultaneously, often credited to American amateur astronomer Leslie Peltier, who spotted the nova during a routine variable star observation using his 6-inch refractor. Peltier's telegram to Harvard College Observatory triggered a worldwide observing campaign involving both professional observatories and amateur astronomers across the northern hemisphere. The 1946 eruption peaked at magnitude +2.5 — slightly fainter than the 1866 event — and lasted approximately two days at maximum brightness. Astronomers at Mount Wilson Observatory recorded the nova's spectrum at multiple stages, tracking ejection velocities of approximately 3,000 km/s. Observations also revealed enhanced mass transfer in the years preceding the eruption, providing crucial evidence for the accretion-triggered nova model. After the 1946 eruption, T CrB faded below magnitude +10 by 1951 and has remained in quiescence ever since. The 80-year cycle — combined with matching pre-eruption brightness fluctuations in the 1930s–1940s and 2010s–2020s — underpins the confident prediction that the next eruption will occur in 2026.
Best Gear for Nova Watching
A nova like T CrB is one of the few astronomical events where binoculars are actually preferable to large telescopes. The nova becomes visible to the naked eye, and binoculars enhance the view without sacrificing the context of the surrounding constellation.
Celestron UpClose G2 10×50 Binoculars
A good pair of 10×50 binoculars is the single best instrument for nova observing. Once T CrB erupts, it will be visible to the naked eye — but binoculars will show its orange-red colour, allow you to track its brightness changes night-to-night, and let you compare it directly to Alphacca and other reference stars in the same field of view. The 10×50 format is handheld-stable and frames Corona Borealis beautifully.
Sky-Watcher Heritage 130P
For observing T CrB in quiescence now (before eruption), a 5-inch aperture is ideal to see the faint +10.2 magnitude star clearly.
Celestron SkyMaster 15×70
15×70 binoculars on a tripod reveal the nova's colour and allow accurate magnitude estimates using the comparison star chart above.
Observing Conditions and Timing
The visibility of T CrB and the quality of your observation depend on several factors that you can optimise. Moon phase is the most important: the nova will be most easily observed near New Moon, when the sky is darkest. In mid-2026, the best New Moon weekends for nova observing are June 13–15, July 13–15, August 11–13 (which coincides with the Perseid meteor shower peak — a spectacular bonus), September 10–12, and October 10–12. During a Full Moon, the glare washes out faint stars, making it harder to see T CrB in its current quiescent state at magnitude +10.2.
Altitude and light pollution also affect your view. From mid-northern latitudes (40°N), Corona Borealis reaches an altitude of 60–70° above the southern horizon during summer evenings — high enough to minimise atmospheric extinction and provide a steady, crisp view. From suburban skies (Bortle 5–6), T CrB at peak magnitude +2 will be easily visible to the naked eye. From urban skies (Bortle 7–9), the fainter comparison stars may be difficult to see, but the nova itself should still be visible at peak brightness because magnitude +2 is bright enough to cut through most light pollution. For the best experience, observe from a dark-sky park where the Milky Way itself provides a stunning backdrop for the nova event.
Corona Borealis's position in the summer sky is ideal for evening observing from May through October. The constellation culminates around 10 PM local time in June and July, placing T CrB at its highest and clearest during the prime evening hours. By September, the constellation is already well-placed at sunset and sets around midnight. Binoculars (10×50 or larger) are the recommended instrument for regular monitoring because they provide a wide enough field to show both T CrB and its comparison stars in the same view, enabling accurate magnitude estimates. A telescope at 40–60× is useful for confirming the nova's colour and for observing the structure of the accretion disk during the eruption's later stages.
How to Contribute: Report Your Observation
Amateur astronomers play a critical role in monitoring T CrB. The AAVSO (American Association of Variable Star Observers) maintains a worldwide network of observers who submit magnitude estimates. You can contribute even with basic equipment:
1. Estimate the Magnitude
Using the comparison stars in the table above, visually compare T CrB to the two nearest comparison stars and estimate its brightness to ±0.1 magnitude. The AAVSO provides detailed training on this method.
2. Submit to AAVSO
Submit your observation at aavso.org/webobs. Use the identifier "T CRB" and your estimated magnitude. Submit even if you see nothing — "fainter than" observations are valuable.
3. Report an Eruption
If you suspect T CrB has begun erupting (it appears significantly brighter than expected), report immediately to AAVSO via their alert system. This is a time-critical observation for professional astronomers worldwide.
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