Astronomers using NASA’s Solar Dynamics Observatory captured stunning images of a significant solar flare on May 5, 2015.

A solar flare is a tremendous explosion on the Sun that happens when energy stored in twisted magnetic fields, usually above sunspots, is suddenly released.

Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to X-rays and gamma rays at the short wavelength end.

The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time.

The first solar flare recorded in literature was on September 1, 1859.

Astronomers classify these events according to their brightness in the X-ray wavelengths.

There are three categories: X-class flares are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere; M-class flares are medium-sized; they generally cause brief radio blackouts that affect the polar regions of our planet; C-class flares are small with few noticeable consequences here on Earth.

The solar flare of 5 May 2015 is classified as an X2.7-class flare: the number provides information about its strength (an X2-class flare is twice as intense as an X1, an X3-class flare is three times as intense).

Solar flares are different to coronal mass ejections – gigantic bubbles of gas threaded with magnetic field lines that are ejected from the Sun over the course of several hours, which were once thought to be initiated by solar flares. Although some coronal mass ejections are accompanied by flares, astronomers now known that most of them are not associated with flares.