Level 1 — Absolute Beginner

Scientists in Japan have found a very old storm from the Sun. The storm happened about 800 years ago.

They looked inside very old trees. Trees grow one ring every year. The rings can show what the air was like long ago.

They also read an old book by a poet. The poet saw a strange red light in the night sky. He wrote it in his diary.

Now we know that big sun storms can happen. We must keep our lights and computers safe from the next one.

Sun

the bright star in the sky that gives us light and heat

storm

a violent event in the air or in space

year

twelve months

tree

a tall plant with a trunk and leaves

ring

a circle, here a layer of wood inside a tree

poet

a person who writes poems

diary

a book where you write what happens every day

computer

a machine that stores and uses information

Level 2 — Elementary

Japanese scientists have used two very different sources to find a hidden solar storm from the early 13th century. The first source is buried asunaro wood from Aomori in the north of Japan. The second is an old diary written by a famous poet.

Trees record the air around them inside their growth rings. When a strong solar storm hits the Earth, more carbon-14 forms in the atmosphere, and trees take it in. The team found a clear spike of carbon-14 dating to roughly 1200–1201 CE.

The poet Fujiwara no Teika kept a diary called the Meigetsuki. In February 1204 he wrote about red lights in the northern sky above Kyoto. Red auroras at low latitudes are a classic sign of a powerful solar event.

The new study, published in Science Advances, shows that around the year 1200 the Sun's activity cycle was only seven to eight years long, instead of the eleven years we see today. Big solar storms can damage electric grids and satellites, so finding old ones helps engineers plan for future events.

century

a period of one hundred years

diary

a book in which a person writes about daily events

growth ring

a layer of wood added to a tree each year

carbon-14

a heavier form of carbon that forms when cosmic rays hit the air

spike

a short, sharp rise in something

aurora

a coloured glow in the night sky caused by particles from space

latitude

the distance north or south from the equator

electric grid

the network that delivers electricity to homes and businesses

Level 3 — Intermediate

A Japanese-led team has pinned down a previously undocumented solar proton event in the early 13th century by combining tree-ring chemistry with the poetic chronicle of a Kamakura-era courtier. The study, published in Science Advances this week, dates the event to between the winter of 1200 and the spring of 1201 CE and places it within the family of so-called Miyake events — sudden, intense bursts of high-energy solar particles that leave a chemical fingerprint deep in the wood of trees alive at the time.

The radiocarbon evidence comes from buried asunaro (Thujopsis dolabrata) recovered from Aomori Prefecture, on the northern tip of Japan's main island. Tightly resolved annual sections of these growth rings revealed a clean spike in carbon-14 abundance corresponding to the 1200/1201 boundary. The team cross-checked the spike against beryllium-10 isotope data from Greenland ice cores, finding a corroborating peak in the same calendar window.

Independently, the researchers consulted Fujiwara no Teika's 'Meigetsuki,' one of the most important Japanese court diaries of its era. In February 1204 CE, Teika describes 'red lights' in the northern sky over Kyoto, an unambiguous account of low-latitude red auroras. Combined with similar Chinese and European sky-watching records, the diaries help anchor a sustained period of elevated solar activity that the team interprets as a string of energetic outbursts following the underlying 1200/1201 event.

The wider implication concerns the Sun's variability. The new chronology suggests medieval solar cycles ran in roughly seven-to-eight-year bursts rather than the eleven-year rhythm familiar from modern observations. That matters because Miyake-type events are the principal historical analogue used by space-weather agencies and electric-grid operators when stress-testing modern power, satellite and aviation infrastructure against an extreme proton-flare scenario.

solar proton event

a burst of high-energy protons emitted by the Sun

Miyake event

a sharp, brief surge in cosmogenic isotopes recorded in tree rings, named after Fusa Miyake

radiocarbon

the carbon-14 isotope used to date organic material

beryllium-10

a long-lived radioactive isotope produced when cosmic rays strike the atmosphere

ice core

a cylinder of ice drilled from a glacier that records past climate and atmospheric data

low-latitude aurora

an aurora seen well away from the polar regions, usually a sign of a strong geomagnetic storm

calendar window

a specific range of dates used to compare different records

space-weather agency

an organisation that monitors and forecasts conditions in near-Earth space

Level 4 — Advanced

A multi-institutional Japanese team has anchored a previously unrecognised solar proton event to the calendar window 1200/1201 CE, drawing simultaneously on tree-ring radiocarbon chemistry, Greenland beryllium-10 ice-core data, and the elegantly observational diaries of Kamakura-era Kyoto. The paper, in Science Advances, places the event within the canon of 'Miyake events' — sudden, high-amplitude excursions in cosmogenic isotopes that mark the passage of an exceptionally energetic burst of solar particles past Earth's atmosphere.

The dendrochemical signal comes from precisely sectioned annual rings of asunaro (Thujopsis dolabrata) recovered from Aomori Prefecture, where waterlogged subsoil preserved the wood at a level of detail rarely matched outside subfossil bog assemblages. Single-ring delta-14-C measurements reveal a step-change of roughly 9 per mille at the 1200/1201 boundary — well above the 6 per mille convention often used to flag a Miyake event. Greenland NEEM-core beryllium-10 abundances spike in the same year window, ruling out a purely local geochemical artefact and pointing to a global atmospheric injection consistent with a sustained burst of high-energy protons.

The textual layer is what gives the paper its breadth. Fujiwara no Teika's 'Meigetsuki' — among the most precisely dated medieval East Asian diaries — describes 'red lights' over the northern sky of Kyoto in February 1204 CE: an unmistakable description of a low-latitude red aurora, only generated by geomagnetic storms in the upper few per cent of the ground-induced-current distribution. Comparable Chinese chronicle entries and a few European astrological notices document repeated bright aurorae through this same span, which the team interprets as the aftermath of an underlying 1200/1201 outburst followed by a roughly four-year tail of heightened solar activity.

Two corollaries deserve emphasis. First, the team's spectral analysis of the medieval radiocarbon series suggests the Sun's modulation in this era ran on a roughly seven-to-eight-year quasi-periodicity, markedly shorter than the canonical eleven-year Schwabe cycle that organises modern space-weather forecasting. Second, Miyake-level events — historically the 774-775, 993-994, and now 1200/1201 cases — define the deterministic worst-case scenario stress-tested by space-weather agencies and grid operators. Knowing that they recur at a non-trivial cadence, and that the Sun's underlying cycle length has varied substantially within just the past millennium, materially tightens the case for hardening transformer infrastructure, satellite radiation shielding and aviation polar-route planning against the next exceedance event.

cosmogenic isotope

an isotope produced by the interaction of cosmic rays with atmospheric atoms

dendrochemical

relating to the chemical composition of tree rings

delta-14-C

the standard measure of relative deviation of carbon-14 from a reference value