Why Do We See Lightning Before Thunder?

If we are watching the sky, we see the lightning before we hear the thunder. That is because light travels much faster than sound waves. We can estimate the distance of the lightning by counting how many seconds it takes until we hear the thunder. It takes approximately 5 seconds for the sound to travel 1 mile.

Why do we see lightning first and then after sometime hear the sound of thunder?

Lightning is seen earlier and thunder is heard later because the speed of sound is 330 m/s and the speed of light is 300,000,000 m/s. Light travels faster than a sound. Thus, light from the lightning reaches first to you. The sound from the lightning takes longer to reach and hence heard later.