The sky over Bulgaria was lit up by an aurora borealis on Sunday. The unusual sight of the red-coloured sky prompted many questions on social networks. 

"Such a phenomenon can be seen from Bulgaria only in rare cases, after a powerful coronal mass ejection from the sun," physicist Pencho Markishki of the Institute of Astronomy at the Bulgarian Academy of Sciences told BTA. After the stream of charged particles bombards the Earth's magnetosphere, the solar plasma particles create the auroras. They can be observed very rarely at lower latitudes, when the process is very intense, the physicist explained. They are accompanied by a geomagnetic storm that can disrupt radio communications, Markisky added.