You hear a Thunder four seconds after you see lightning how far away is the storm

After you see a flash of lightning, count the number of seconds until you hear the thunder. (Use the stop watch or count "One-Mississippi, Two-Mississippi, Three-Mississippi," etc.) For every 5 seconds the storm is one mile away. Divide the number of seconds you count by 5 to get the number of miles.

Explanation:

second mirror gathers light from a faraway object and reflects it to another mirror. - a.