Calculate travel time at the speed of light, convert distances to light years and light minutes, and explore relativistic effects. Covers light seconds, light minutes, and light years.
The speed of light in a vacuum is exactly 299,792,458 metres per second (approximately 300,000 km/s or 186,000 miles per second). It is denoted by the letter c and is the universal speed limit.
The average Earth-Sun distance (1 AU) is about 150 million km. At 299,792 km/s, light takes approximately 8 minutes and 20 seconds to reach Earth from the Sun.
The Moon is approximately 384,400 km away. Light takes approximately 1.28 seconds to travel from Earth to the Moon.
A light year is the distance light travels in one year — approximately 9.461 × 10¹⁵ metres, or about 9.46 trillion kilometres. It is a unit of distance, not time.
According to special relativity, time passes more slowly for a moving observer compared to a stationary one. At 90% of the speed of light, a traveller ages 2.3 times more slowly than a stationary observer. This is the Lorentz factor.
In one second, light travels 299,792 kilometres — enough to circle Earth 7.5 times, or travel from Earth to Moon and back in about 2.56 seconds.
Proxima Centauri, the nearest star to Earth after the Sun, is 4.24 light years away. At the speed of light, the journey would take exactly 4.24 years. At current spacecraft speeds, it would take over 70,000 years.