What is the speed of light 2

Propagation of light

In the animation you can see that the emitted light of the laser only arrives at the receiver after 2.5 seconds and is registered. So light also needs time to get from one place to another. You can now calculate the speed of light from the distance of the moon to the earth and the measured arrival time of the light flash at the receiver. The distance moon - earth is 384400 km (In the animation this was rounded to 380000 km for the sake of simplicity. The light has to cover this distance twice, once on the way to the moon and once on the way back to the receiver on earth. The measured time is about 2.5 seconds. \ [v _ {\ rm {light}} = \ frac {\ rm {distance}} {\ rm {running time}} = \ frac {2 \ cdot 384400 \, \ rm {km}} { 2.5 \, \ rm {s}} = 307520 \, \ rm {\ frac {km} {s}} \] Light spreads very quickly. With other measurement methods, the speed of light can be determined more precisely. In a vacuum is the speed of light, which is often used in formulas c is referred to, \ (299.792.458 \, \ rm {\ frac {m} {s}} \). That is about \ (300,000 \, \ rm {\ frac {km} {s}} \).

Due to the great distance between the sun and the earth, light that is emitted by the sun needs about 8 minutes and 20 seconds before it reaches us on earth.

Perception of the speed of light in everyday life

When a light source is switched on, the light is not "there immediately" at a remote location, but it takes a certain time for the light to reach the receiver from the source. At the usual distances in the range of meters or kilometers, however, this transit time of the light is so short that you have the impression that the light is there "instantly".