"First-look data from Stereo-B are not sufficient to determine if the cloud is heading for Earth," astronomer Tony Phillips wrote on his website Spaceweather.com, which monitors space weather events. "Our best guess is 'probably, yes, but not directly toward Earth.' A glancing blow to our planet's magnetosphere is possible on March 8th or 9th." [Worst Solar Storms in History]
According to Phillips, the big X5.4 solar flare erupted from the giant active sunspot AR1429, which was also responsible for the major sun storm on Sunday.
When aimed directly at Earth, X-class solar flares can endanger astronauts and satellites in orbit, interfere with satellite communications and damage power grids on Earth. They can also amplify the Earth's display of northern and southern lights, also known as auroras. Charged particles from the solar storms can interact with Earth's upper atmosphere, resulting in a glow that is typically visible to observers at high northern or southern latitudes.
Astronomers rank solar flares by strength using five categories: A, B, C, M and X. The A-class flares are the weakest sun storms, while the X-class events are the most powerful solar flares.
This ranking system was designed by the National Oceanic and Atmospheric Administration and resembles the Richter scale used for earthquakes in that each category is 10 times stronger than the one before it, NASA officials have said. So a B-class solar flare is 10 times stronger than an A-class event, while a C-class solar storm releases 10 times more energy than B-class flare (or 100 times more energy than an A-class event).
The categories are also broken down into subsets, from 1 to 9, to pinpoint a solar flare's strength. Only X-class solar flares have subcategories that go higher than 9. The most powerful solar flare on record occurred in 2003 and was estimated to be an X28 on the solar flare scale, NASA officials said.