In May 1921, a giant sunspot erupted, ejecting masses of solar material towards the Earth. This solar storm produced auroras visible all the way to the equator, and a rash of fires.
A telegraph exchange in Sweden was the first to burst into flames, followed by a control tower near New York’s Grand Central Station. Long stretches of telegraph wire were acting as aerials; the resulting induced currents were strong enough to blow fuses and cause overheating, sometimes resulting in fires.
Telegraph services were disrupted in the US, UK and across much of the rest of the world, including Australia. Railway signalling was also affected, and in Scandinavia and Canada some telephone lines were put out of action.
Scientists had difficulty assessing the magnetic strength of the New York Railroad Superstorm because it went off the scale of their instruments. It was certainly comparable to the Carrington Event of 1859, often considered the biggest known solar storm.
The next once-in-a-century storm will likely have more serious impact, due to the increase in infrastructure. We can expect power blackouts, satellite navigation failures and other issues. The UK’s Space Environment Impacts Expert Group recently put forward proposals for planning for and mitigating such a storm, comparing it to the slight but predictable risk of a pandemic.
