X-class solar flares are the most powerful eruptions on the sun. When aimed directly at Earth, X-class flares can potentially pose a danger to astronauts and spacecraft in space, and interfere with navigation, radio and communications signals. M-class flares are ranked as moderate sun storms that can supercharge the Earth's aurora displays. There are also weaker classes of solar storms that have little effect on Earth, including C-class, B-class and even A-class storms.  - See more at: