Lights and colors of lightning and thunder

The lightning is accompanied by sound waves and a sound called thunder that results from the lightning heating the air and causing its expansion, just as thunder occurs immediately after the appearance of the lightning flash. As for the sound waves of thunder, the reason is that the sound waves coming from the distant parts arrive later than those coming from the nearby parts. The resulting time delay causes the time difference between the flash of lightning and the sound of thunder, as the time period was estimated to be about 3 seconds per 1 km.