Thunder is the noise that lightning makes. Lightning erupting is was causes it. If you are standing right next to lightning, you can tell that the sound (thunder) happened at the same time as the lightning.

As you move farther away from the lightning, the sound happens at a different time as the lightning. This is because the sound travels much slower than the light! The light waves come to our eyes way faster than the sound waves come to our ears.

Thunder is actually caused by lightning.When lightning travels from the sky to the ground, a pocket of air is opened. When the light disappears, the pocket of air closes and in the process generates sound (thunder)! Because of this, you'll notice that in a lightning storm, you usually see lightning first, then hear thunder! I hope this helps!

Thunder is a shockwave created by the hot plasma of a lightning bolt exploding into the surrounding air. The electrical current of the lightning heats the air until it becomes a plasma, about 11,000 degrees. Being at the same density as the air around it but at a much higher temperature, the plasma expands, explosively, outward. This explosion creates a shockwave, which you then hear as a thunderclap.

To explain thunder, you have to start with lightning. During a storm, electrical charge builds up in clouds, with an opposite charge building up on the earth below, like a huge battery. When the charge gets high enough, the energy that has been built up is released as a lightning bolt. As this energy is released, the air around the lightning bolt reaches a very high temperature and pressure. The pressurized region travels outward from the lightning bolt as a wave, reaches your ear, and you hear the rumble of thunder.