The solar storm of 1859

Also known as the Carrington Event, the solar storm of 1859 was a powerful geomagnetic storm. An incredible storm of charged particles sent by the Sun slammed into Earth’s atmosphere, overpowered it, and caused havoc on the ground. Telegraph wires, the high-tech stuff of the time, suddenly shorted out in the United States of America and Europe, igniting widespread fires. Colourful aurora, normally visible only in Polar Regions, were seen as far south as Cuba and Hawaii.

Earth’s magnetic field normally protects the surface of the planet from some storms. In 1859, the planet’s defences were totally overwhelmed. Over the past decade, similar but less powerful storms have likewise busted through, giving scientists insight into what will eventually happen again.

Geomagnetic storm

A geomagnetic storm (commonly referred to as a solar storm) is a temporary disturbance of the Earth’s magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth’s magnetic field.

The disturbance that drives the storm may be a solar coronal mass ejection (CME) or a co-rotating interaction region (CIR), a high speed solar wind originating from a coronal hole (areas where the Sun’s corona is colder, hence darker, and has lower-density plasma than average because there is lower energy and gas levels). The frequency of geomagnetic storms increases and decreases with the sunspot cycle. During solar maximum (a regular period of greatest Sun activity during the 11-year solar cycle), geomagnetic storms occur more often, with the majority driven by CME’s. During solar minimum, storms are mainly driven by CIR’s (though CIR storms are more frequent at solar maximum than at minimum).

The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind’s magnetic field interacts with the Earth’s magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and ionosphere. During the main phase of a geomagnetic storm, electric current in the magnetosphere creates a magnetic force that pushes out the boundary between the magnetosphere and the solar wind.

The largest recorded geomagnetic storm, the Carrington Event in September 1859, took down parts of the recently created U.S. telegraph network, starting fires and shocking some telegraph operators. In 1989, a geomagnetic storm energised ground induced currents that disrupted electric power distribution throughout most of Québec and caused aurorae as far south as Texas.

The solar storm of 1859

From August 28 to September 2, 1859, many sunspots (temporary phenomena on the Sun’s photosphere that appear as spots darker than the surrounding areas) appeared on the Sun. On August 29, southern auroras were observed as far north as Queensland, Australia. Just before noon on September 1, the English amateur astronomers Richard Carrington and Richard Hodgson independently recorded the earliest observations of a solar flare.

Richard Carrington and Richard Hodgson compiled independent reports which were published side-by-side in the Monthly Notices of the Royal Astronomical Society, and exhibited their drawings of the event at the November 1859 meeting of the Royal Astronomical Society.

The flare was associated with a major coronal mass ejection (CME) that travelled directly toward Earth, taking seventeen and a half hours to make the one hundred and fifty million kilometre journey. It is believed that the relatively high speed of this CME was made possible by a prior CME, perhaps the cause of the large aurora event on August 29, 1859 that “cleared the way” of ambient solar wind plasma for the Carrington Event.

On September 1859, one of the largest recorded geomagnetic storms (as recorded by ground-based magnetometers) occurred. Auroras were seen around the world, those in the northern hemisphere as far south as the Caribbean; those over the Rocky Mountains in the U.S. were so bright that the glow woke gold miners, who began preparing breakfast because they thought it was morning.

People in the north-eastern United States of America could read a newspaper by the aurora’s light. The aurora was visible from the poles to the low latitude area, such as south-central Mexico, Queensland, Cuba, Hawaii, southern Japan and China, and even at lower latitudes very close to the equator, such as in Colombia.

Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks. Telegraph pylons threw sparks. Some telegraph operators could continue to send and receive messages despite having disconnected their power supplies. “Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the Moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested”.

The Carrington Event had great contemporary importance in Victorian science. It heightened an already increasing interest in Sun-Earth connections, and helped stimulate astronomers to look for further connections, including possible solar influences on terrestrial weather that might be used to predict droughts and associated famines.

However, the event’s significance for the twenty-first century is that it was one of the most powerful solar explosions ever recorded. The largest flare of modern times occurred on November 4, 2003. This originated in a complex sunspot group similar to the one that caused the Carrington Event. Across much of its passage across the Sun the previous two weeks, the 2003 sunspot had been unleashing many flares and CMEs.

These had not only sparked powerful aurorae: the magnetic effects caused damage to communications satellites and some airlines flying near the arctic regions had to be re-routed, due to dangerous radiation levels in the upper atmosphere. By November, when the most powerful flare took place, the parent sunspot was moving off the Sun’s visible disc and the resulting CME was directed at ninety degrees to the Earth. Had it travelled directly towards the Earth, its consequences for communications systems and transport could have been devastating.

Research by scientists into the recorded magnetic effects of the solar storm of 1859 suggests that it might well have been as powerful as the 2003 one. The explosion’s effects on the Victorian electric telegraph were as nothing to the consequences of a Carrington-type event for the communications and power supplies we rely on in the modern world. That is why the solar storm of 1859 forms a benchmark for a potentially disastrous modern-day space weather event – and why scientists and governments need to understand and monitor the Sun’s emissions, in preparation for another such event.