Lighttime: Calculator Time and Distance of Light
Calculate distance per time or time per distance at the speed of light. Light spreads at a constant and very high speed. Here the distance in meters and kilometers that the light travels in a certain time can be calculated, or it is calculated how long it takes for a given distance. The speed of light in vacuum is preset. In the case of the light year, the year is calculated with exactly 365.25 days. Please enter time or distance to calculate the other value. For time, it is enough to enter one of the five values.
The abbreviation AU at distance stands for astronomical units. One astronomical unit is defined as exactly 149597870700 meters, or just under 150 million kilometers. This corresponds to the average distance from Earth to the Sun. Light takes 8 minutes and 19 seconds to travel this distance.
Examples: The moon is on average 384400 kilometers away from us, so the light takes about 1.3 seconds to reach it. In 10 hours, light travels almost 10.8 billion kilometers. In 10 years it reaches a distance of 94.607 trillion kilometers, or of course 10 light years. That's just over 3 parsecs, or parallax seconds. The parallax second is the largest commonly used astronomical unit of length.
Light time, or the more commonly used term light year, are sometimes colloquially used to refer to time. But this is wrong, they are actually measurements of length. Generally, time and length can be converted into one another by a speed. Since the speed of light is constant according to the special theory of relativity, developed by Albert Einstein in 1905, a length can be calculated precisely from the time it takes light to travel the corresponding distance.
Last updated on 06/30/2025. Author: Jürgen Kummer
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