Find how long light, radio or a laser signal takes to cross any distance, from a fibre-optic cable to another galaxy. Choose a preset like the Sun or Proxima Centauri, or enter your own distance in km, miles, AU, light-years or parsecs.
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Estimate the delay talking to a Mars rover.
Find the minimum delay over a fibre route.
See how old the starlight you see really is.
Even at 300,000 km per second, light takes noticeable time on cosmic scales. When you look at the Sun you see it as it was about 8 minutes ago, and the light from the Andromeda galaxy left it about 2.5 million years ago.
Planetary distances change as orbits move, so presets for Mars, Jupiter and Saturn use typical or closest-approach values. Mars, for example, is between about 3 and 22 light-minutes away.
299,792 km, about 78% of the way to the Moon.
18 million km.
9.46 trillion km.
Exactly 299,792,458 metres per second in a vacuum, about 300,000 km/s or 186,282 miles per second.
About 8 minutes 19 seconds on average, because the Sun is about 149.6 million km (1 AU) away.
About 1.28 seconds at the average distance of 384,400 km, so a radio round trip is about 2.6 seconds.
Light slows down in any material by its refractive index. Glass fibre has an index of about 1.47, so signals travel at roughly 204,000 km/s, about 4.9 microseconds per kilometre.
No, it is a distance: how far light travels in one Julian year, about 9.46 trillion km.
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