Hi,

Our current definition of solar storms encompasses a wide range of phenomena, not all of which were possible to observe long ago. We have records and indications of people observing sunspots going back to 800 BC (and some suggestion of well before that). I think one of the first times someone connected activity on the Sun with geomagnetic activity was Edward Sabine in 1852.

In terms of observing solar flares and connecting them to effects on Earth, it was Richard Carrington that noted the great event of 1859. This is still considered to be the biggest solar storm/geomagnetic storm that the Earth has experienced. The magnetic response of the Earth actually induced currents in telegraph machines that gave their operators shocks and even set paper on fire, as well as causing aurora to be seen as far south as Mexico and Hawaii.

Most of us believe that if such a strong event happened these days it would disable many of our satellites and cause power failures over large swaths of the world. Some estimates put the cost of recovering from such an event at $40 billion per day! This is one of the reasons we're working to be able to understand and then predict these events and the Earth's response. Given enough lead time power companies and satellite operators can take action to protect equipment.

-Christina