Scientists classify the severity of solar flares according to the amount of X-rays they emit, known as X-ray flux. The GOES satellite measures the X-rays coming from the sun at any given time—see the graph of live data below.

Looking at this graph, you can easily identify flares as sharp spikes—the higher the spike, the larger the flare. A spike that reaches up into the zone marked 10 ^-5 or higher is likely to have effects here on earth. Spikes that don’t reach this high are generally inconsequential flares.

Use the horizontal scale (Universal Time) to figure out when the flare happened. The data on this graph are automatically updated every five minutes.