A solar flare isn't just an explosion of hot gases. It pushes out waves of light all across the spectrum. That includes light we can't see -- including radiation in the form of X-rays and gamma rays. These rays can be dangerous to humans. Fortunately, the Earth's atmosphere absorbs most of these high-energy rays.
That's not to say everyone is in the clear after a solar flare. Humans in space or at high altitudes -- on board an airplane, for example -- could risk exposure to intense radiation. Short-term damage could include skin irritation. Long-term consequences might include an increased risk of developing skin cancer. But it's likely that any affected human would eventually recover from the exposure.
Electronics are also vulnerable to these rays. If high-energy rays were to hit a satellite, they could strip electrons from the metal components, ionizing them. As electrons break free, they could short out the electronics within a satellite. They could also create a magnetic field that would damage the satellite's systems. Some satellites have shielding to protect them from these rays, but many are still vulnerable.
Because our atmosphere absorbs most of these dangerous rays, terrestrial systems are fairly safe from solar flares. But another solar event called a coronal mass ejection (CME) can cause serious problems for electrical systems here on Earth. During a CME, the fluctuations of the sun's magnetic fields cause a large portion of the surface of the sun to expand rapidly, ejecting billions of tons of particles out into space. Sometimes CMEs accompany solar flares -- but not all solar flares produce CMEs and not all CMEs accompany solar flares.
Unlike a solar flare, a CME doesn't produce intense light. But it does produce a magnetic shockwave that extends billions of miles out into space. If Earth is in the path of that shockwave, our planet's magnetic field will react to the event. It's similar to what happens if you put a weak magnet next to a strong one. The weak magnet's field will align itself to the strong magnet's field. A magnetic shockwave from the sun could cause the alignment of the Earth's magnetic field to shift unpredictably.
Pretty lights aren't the only consequence from a CME. The magnetic fluctuations can cause compasses to fail. And since magnetic fields can induce electricity, any conductor could become an inductor. A powerful CME could induce electricity in large, powerful conductors. That could overload electrical systems and cause massive damage.
Next, we'll take a look at exactly how badly off we could be after a massive CME event.