Tales of Hyperborea

At the heart of our solar system our star, the Sun, consists of a vast and tumultuous tangle of magnetic fields, invisibly stretching outwards to Earth and beyond. Charged particles race out from this unfathomably powerful nuclear fusion reactor and on arrival they interact with Earth’s magnetic field. That field, which acts like a shield around our planet, buckles and deforms in response to the imposing power of the Sun. Humans have experienced the tangible effects of this power during peaks in solar activity such as the 19th century ‘Carrington Event’. This saw the visibility of the Aurora Borealis extend as far south as Mexico and Italy, bright enough to read by. These natural light shows are the result of charged solar particles racing along the magnetic field lines that loop from pole to pole like a jumbo-sized bar magnet. When the particles collide with our atmosphere, they excite atoms of Oxygen and Nitrogen, which in turn release energy in the form of green and reddish light. Earth observation satellites can observe the aurorae from high above as a ring of red and green light around each pole.

Alongside these amplified auroral displays during the Carrington Event of September 1859, there were reports of sparking telegraph lines and garbled messages as the changing magnetic fields generated a ground current travelling along the best conductors available at that time - only a few hundred miles of copper wires. Today, with our insatiable preoccupation with electronics, we study the Sun in part to safeguard our technologically fragile society. Through an eleven-year cycle of ebbing and flowing solar activity, Earth and humanity are subject to geomagnetic storms, often called ‘solar storms’. They can wreak havoc upon satellites, radio communication and power supplies alongside breath taking and geographically widespread aurorae.

The origin of these solar storms are rooted in dark marks on the Sun’s surface called sunspots - ‘cool’ spots enclosed by transient magnetic activity. In centuries past, these were sometimes misinterpreted as planets between the Earth and the Sun, and more wildly as a parting in the Sun’s atmosphere to peer into a dark and solid surface beneath that we know today does not exist. Prior to this, ancient Sun-worshipping civilisations were struck with fear when large sunspots were seen through the smoke of forest fires or thick fog - ghastly blemishes on an otherwise perfect disc of pure light.

Much of our understanding of the Sun is owed to a convergence of science, society, and invention. This is exemplified by early photographic techniques that safely and accurately captured the blinding light of the Sun to record solar features, surpassing sketching via projection through a glass lens onto a white surface.

Many of the pieces in the exhibition evoke early experimentation in solar photography with the stark contrast of white on black. With the modern imaging systems of today, features seen include the fine hair-like structures around the edge of the solar disc called spicules, and gradients of dark to light that surround each dark sunspot called the penumbra. Before the advent of space telescopes and digital photography, experiments in glass and chemistry were the key to unlocking solar secrets.

With techniques developed over centuries, solar physicists are equipped with a full arsenal of tools to better predict solar storms. And yet, with no control over the Sun’s activity, we can only mitigate damage by taking measures such as backing up data storage, temporarily shutting down power facilities and elevating satellites. The magnetic mysteries of the Sun have yet to be unravelled in their entirety as we remain uncertain of the grand magnetic cycles deep in the solar interior. We can model magnetic activity, but such is the dynamic complexity of the Sun’s makeup that we are only making crude sketches that allude to its true nature. However, with each new solar observatory and advancement in computing power the sketch is refined and clarified, bringing us ever closer to a more complete understanding of the Sun and its mysteries.

Brendan Owens, December 2021

Astronomer Emeritus for the Royal Observatory Greenwich and researcher at Trinity College Dublin.