A solar flare and a coronal mass ejection (CME) both erupted from the Sun on the summer solstice — June 20, 2013, right around 11:24 pm. The CME was Earth-directed, but not of particular strength — a mild geomagnetic storm is expected. According to current NASA estimates, the CME left the Sun at speeds of about 1350 miles per second. The estimates are based on observations taken by NASA’s Solar Terrestrial Relations Observatory and the ESA/NASA’s Solar and Heliospheric Observatory.
A coronal mass ejection (CME) is a type of solar eruption that results in huge masses of particles being sent into space at very high speeds — if Earth-directed these particles typically reach the Earth within 1-3 days. The particles typically cannot make it through the atmosphere though, so humans themselves are usually unaffected, but electronic systems and satellites are often affected.
Earth-directed CMEs can cause a space weather phenomenon called a geomagnetic storm, which occurs when they funnel energy into Earth’s magnetic envelope, the magnetosphere, for an extended period of time. The CME’s magnetic fields peel back the outermost layers of Earth’s fields changing their very shape. Magnetic storms can degrade communication signals and cause unexpected electrical surges in power grids. They also can cause aurora. Storms are rare during solar minimum, but as the sun’s activity ramps up every 11 years toward solar maximum — currently expected in late 2013 — large storms occur several times per year.
The eruptions also pose a significant theoretical problem with regards to travel through deep space — such as would be necessary during a trip to Mars. Without significant shielding astronauts exposed to theses eruptions could face significant health problems.