The Sun looks like the one fixed, unchanging thing in the sky, and for almost all of human history that is exactly what it was assumed to be. Berman’s book is the story of how we learned it has a pulse, a violent temper, and a lifespan, and how each of those discoveries came from a stubborn amateur or a ridiculed outsider rather than the establishment.
The eleven-year heartbeat and the men who found it
The title refers to a real, measurable rhythm. Roughly every eleven years the Sun’s sunspot count swells to a maximum and then subsides to a near-blank minimum, and this cadence turns out to govern flares, auroras, and even small swings in Earth’s temperature. Nobody was looking for it. Heinrich Schwabe, a German pharmacist and amateur astronomer, spent seventeen years staring at the Sun hoping to catch a hypothetical planet crossing its face inside Mercury’s orbit. He never found the planet, but by 1843 his obsessive daily sunspot tallies had revealed a cycle nobody had suspected. Rudolf Wolf later dug back through old records, pinned the average period near eleven years, and created the sunspot-counting standard still used today. Walter and Annie Maunder added the strangest piece: their “butterfly diagram” showed that each cycle’s spots begin at high solar latitudes and march toward the equator as the cycle ages. Sunspots themselves are not holes or cinders but knots of ferocious magnetism, thousands of times stronger than Earth’s field, which chokes off the heat rising from below and leaves those patches cooler and therefore darker. The deeper machinery, an internal shear layer called the tachocline where the Sun’s rotation changes character, was not even identified until 1989.
How a star burns, and the ghost particles that prove it
The Sun runs on nuclear fusion, welding hydrogen into helium in the crushing heat of its core, and the tiny mass lost in each reaction becomes energy by Einstein’s E=mc2. The numbers are absurd on a human scale. The Sun sheds about four million tons of itself every second and pours out energy equivalent to many trillions of Hiroshima bombs each second, and it has done so for billions of years. A photon born in the core does not simply fly out. It ricochets through the dense interior in a random walk that can take anywhere from tens of thousands of years to roughly a million years before it reaches the surface, after which the trip to Earth takes a mere eight minutes and nineteen seconds. Fusion also spits out neutrinos, and their story is one of the book’s best. Wolfgang Pauli proposed the particle in 1930 to balance the books of a decaying neutron, Enrico Fermi named it “little neutral one,” and for decades no one could catch one. Ray Davis finally did, using a hundred thousand gallons of dry-cleaning fluid parked a mile underground in the Homestake gold mine in South Dakota, counting the rare argon atoms a passing neutrino would create. He kept finding only about a third of the neutrinos theory demanded, a “missing neutrino” scandal that dragged on until 2001, when a heavy-water detector in an Ontario nickel mine showed that neutrinos morph between three types in flight. Davis had been right all along, and won a share of the 2002 Nobel Prize.
Space weather, and the day the Sun reached out and touched our machines
When the Sun’s tangled magnetic field snaps and reconnects, it can hurl ten billion tons of charged particles outward as a coronal mass ejection, traveling at a million miles an hour or more. If one strikes Earth and its magnetism happens to point opposite ours, it dumps its energy into our atmosphere instead of sliding harmlessly around the magnetosphere. The benchmark disaster is the Carrington Event of late August and September 1859, the largest recorded solar storm, when a flare doubled the brightness of part of the Sun’s disk and the ejection reached Earth in only eighteen hours. Telegraph wires, the era’s only long cables, sparked and shocked operators, some of whom were knocked unconscious, and auroras blazed as far south as Cuba. A modern repeat would be catastrophic, because we have wrapped the planet in exactly the infrastructure such storms destroy. On March 13, 1989, a far smaller storm cascaded through Hydro-Québec’s grid in about ninety seconds, cut off 9,460 megawatts, and plunged three million people into a freezing blackout. The 2003 “Halloween storm” rerouted airline flights, forced space-station astronauts into shelter, and fried satellites. A 2008 government study estimated that a true Carrington-scale event today could cause one to two trillion dollars of damage in its first year and take four to ten years to recover from. A fleet of spacecraft, SOHO, ACE, GOES, STEREO, and SDO, now watches the Sun continuously, though ACE parked sunward of us gives only an hour or two of firm warning.
The impossible coincidence: eclipses and the geometry of totality
Berman treats a total solar eclipse as the single most powerful sight a human can witness, and insists a 99-percent partial eclipse is no substitute at all. The reason totality exists is a fluke: the Moon is about four hundred times smaller than the Sun but also four hundred times closer, so the two disks appear almost exactly the same size. That coincidence is temporary, because the Moon drifts away about an inch and a half a year, and in roughly seventy million years total eclipses will end forever. The ancients cracked the timing anyway. The Babylonians noticed that an eclipse repeats after eighteen years and about eleven days, a period the Greeks adopted under the name saros, and three saroses (an “exeligmos,” fifty-four years and a month) bring the shadow back to nearly the same place on Earth. During totality the sky darkens, stars appear, shadow bands ripple across the ground, and the corona blazes into view, a plasma structure whose shape betrays where in the eleven-year cycle the Sun sits. The United States endured a thirty-eight-year eclipse drought before the August 21, 2017 totality, with a second following on April 8, 2024.
The Sun’s grip on Earth’s climate
The Sun’s variability leaves fingerprints on climate, most famously the Maunder Minimum of roughly 1645 to 1715, a stretch when sunspots nearly vanished and Europe shivered through the depths of the Little Ice Age. But short solar swings cannot explain ice ages, and here Berman credits the Serbian astrophysicist Milutin Milankovitch, initially ignored, later vindicated by deep-sea sediment cores in 1968. Ice ages track slow changes in Earth’s orbit and tilt: the eccentricity of our orbit over about a hundred thousand years, the tilt of the axis swinging between 22.1 and 24.5 degrees over roughly 41,000 years, and the precession of the axis over some 26,000 years. The other great lever is the atmosphere. The British engineer Guy Callendar argued in 1938, well ahead of his peers, that human fossil-fuel burning was measurably raising carbon dioxide and warming the planet. Over the past 780,000 years CO2 swung between about 180 and 280 parts per million; human activity has pushed it past 388 and climbing. Berman lays out four competing influences on temperature: the Sun’s changing brightness, volcanic dust, El Niño, and carbon dioxide. Solar variability dominated the record until about the mid-1990s, which is precisely when rising CO2 overtook it, making the Sun no longer the prime mover. The unusually deep, prolonged solar minimum around 2006 to 2009 briefly masked warming, buying time the book warns we may squander.
Auroras and the sky’s quieter gifts
Auroras are space weather made beautiful. The pieces fell into place through outsiders again: Eugene Parker, ridiculed in the 1950s, correctly insisted the Sun blows a constant “solar wind” spiraling outward, and James Van Allen, using instruments aboard Explorer 1 in 1958, discovered the radiation belts of the magnetosphere that trap solar particles. When charged particles funnel down near the magnetic poles, they excite oxygen sixty to two hundred miles up, and as excited electrons drop back they emit a characteristic pale green at 557.7 nanometers, with a rarer deep red at 630 nanometers. The currents involved are enormous, millions of amps and tens of thousands of volts. Auroras encircle each pole in a glowing oval, brightest for observers under it near Fairbanks, and the southern lights mirror the northern ones second by second. Alone among these spectacles the aurora rises and falls with the eleven-year heartbeat. Berman rounds out the chapter with the Sun’s steadier optical gifts, rainbows arcing 42 degrees around the point opposite the Sun, halos and sun dogs from ice crystals, and iridescent clouds, phenomena that, unlike the aurora, depend on Earth’s water and ice rather than on the solar cycle.
The life and death of the Sun
The Sun is not like us, and Berman spends the final chapter on how differently a star ages. It has been brightening about ten percent every billion years, and in roughly 1.1 billion years it will grow hot enough to boil away Earth’s oceans and stabilize surface temperatures near 710 degrees Fahrenheit, ending complex life long before the Sun itself changes much. About four billion years after that, its core chemistry shifts toward fusing helium into carbon and oxygen, its outer layers balloon to near Earth’s orbit, and it becomes a red giant, cool-surfaced and orange, a hundred times its present width. The red-giant phase lasts less than a billion years before the core’s final fusion flares blow off the outermost one percent as a glowing shell, a “planetary nebula” (a misnamed object with nothing to do with planets) lit by a central star seething at 180,000 degrees. That ring fades in about fifty thousand years. What remains collapses under gravity until quantum mechanics intervenes, with electron degeneracy pressure halting the fall at roughly Earth’s size: a white dwarf, a sphere of crushed carbon and oxygen so dense a cupful outweighs a cement truck. It then simply cools, over an unimaginably long time, to a cold, dark, perfectly smooth black dwarf, a process whose full span is about twenty billion years, so long that the universe is not yet old enough for a single black dwarf to exist. The Sun’s most extreme adventures, Berman notes, all happen only after it has already destroyed every living thing that depended on it.
Lessons worth keeping
- The Sun has a measurable pulse, an eleven-year sunspot cycle, and it was found by an amateur hunting for something else entirely.
- Nearly every breakthrough here (Schwabe, Parker, Van Allen, Callendar, Milankovitch, Davis) came from someone initially ignored or ridiculed.
- Fusion converts four million tons of the Sun to energy per second, and a photon may take up to a million years to escape the core before its eight-minute trip to Earth.
- Our modern grid, satellites, and aircraft are exactly what a Carrington-scale solar storm would wreck, and the warning time is minimal.
- The Moon being 400 times smaller and 400 times nearer than the Sun is a temporary coincidence that makes total eclipses possible.
- The Sun drove Earth’s climate until the mid-1990s, when rising CO2 overtook solar variability as the dominant factor.
- Stars do not die like people; the Sun’s fate runs from red giant to white dwarf to black dwarf over about twenty billion years.
Sources
- Book: The Sun’s Heartbeat by Bob Berman