A little after midnight in the late summer of 1859, campers dozing beneath the night sky in the Colorado Rockies woke to a display of auroral light “so bright one could easily read common print.” In their account of the event, published in the Rocky Mountain News, the party recalled that “some insisted it was daylight and began the preparation of breakfast.”

Thousands of miles away, crowds gathered in the streets of San Francisco with eyes turned skyward. “The whole sky appeared to undulate something like a field of grain in a high wind; the waters of the Bay reflected the brilliant hues of the Aurora,” wrote one journalist in the San Francisco Herald on September 5, 1859. “Nothing could exceed the grandeur and beauty of the sight; the effect was almost bewildering and was witnessed with mingled feelings of awe and delight by thousands.” City dwellers around the world shared this experience.

The two-day celestial event did more than inspire poetic musings and temporarily confuse songbirds who began chirping in the night. Almost immediately, the world’s 100,000 miles of telegraph lines fell silent, victim to a wave of space-borne electric current strong enough to fry the systems. The communications system of the time fell “so completely under the influence of the Aurora Borealis that it was found utterly impossible to communicate between the telegraph stations.”

These famous few days were termed the Carrington event, named after a British astronomer who connected the phenomenon with a huge solar flare that sent charged electrons and protons into the Earth’s magnetic field.

The History of the Cosmos, Hidden in Trees

While humanity stood frozen in bewilderment, awe, and sometimes terror, a Japanese cedar on Yaku Island silently gulped up carbon dioxide, converting the gas to sugar and embedding some of the carbon within its millimeter-thin growth rings.

Around 150 years later, in 2012, Nagoya University graduate student Fusa Miyake was carefully studying the faint growth rings of this 1,900-year-old Japanese cedar, which had been felled in 1956. Miyake was looking for a story bound in the cellulose of the tree’s rings. Specifically, she was looking for a surge of carbon-14.

Also called radiocarbon, carbon-14 is a slightly heavier version of the stable element carbon, or carbon-12. Whereas carbon-12 has six protons and neutrons, carbon-14 has six protons and eight neutrons. Carbon-14 is unstable and decays over time. This isotope accounts for around one part in one trillion of the carbon moving through the global carbon cycle. Still, its signal is strong enough for researchers to distinguish radiocarbon from stable carbon in organic remains such as tree rings.

However, the concentration of carbon-14 can vary. Most notably, violent space weather events, like the solar flare responsible for the 1859 Carrington event, can unleash short, exceptionally intense showers of high-energy particles and increase the atmospheric con