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A light-year is the distance light travels in one Julian year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away.
Earth orbit (yellow) compared to a circle (gray) Earth orbits the Sun at an average distance of 149.60 million km (8.317 light minutes, 92.96 million mi) [1] in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes 365.256 days (1 sidereal year ), during which time Earth has traveled 940 million km ...
This is because the distance between Earth and the Sun is not fixed (it varies between 0.983 289 8912 and 1.016 710 3335 au) and, when Earth is closer to the Sun , the Sun's gravitational field is stronger and Earth is moving faster along its orbital path. As the metre is defined in terms of the second and the speed of light is constant for all ...
By timing the eclipses of Jupiter's moon Io, Rømer estimated that light would take about 22 minutes to travel a distance equal to the diameter of Earth's orbit around the Sun. Using modern orbits, this would imply a speed of light of 226,663 kilometres per second, 24.4% lower than the true value of 299,792 km/s.
A light-minute is 60 light-seconds, and so the average distance between Earth and the Sun is 8.317 light-minutes. The average distance between Pluto and the Sun (34.72 AU) is 4.81 light-hours. Humanity's most distant artificial object, Voyager 1, has an interstellar velocity of 3.57 AU per year, or 29.7 light-minutes per year.
Halley's Comet on an eccentric orbit that reaches beyond Neptune will be moving 54.6 km/s when 0.586 AU (87,700 thousand km) from the Sun, 41.5 km/s when 1 AU from the Sun (passing Earth's orbit), and roughly 1 km/s at aphelion 35 AU (5.2 billion km) from the Sun. Objects passing Earth's orbit going faster than 42.1 km/s have achieved escape ...
They set a limit on the anisotropy of the speed of light resulting from the Earth's motions of Δc/c ≈ 10 −15, where Δc is the difference between the speed of light in the x- and y-directions. As of 2015, optical and microwave resonator experiments have improved this limit to Δc/c ≈ 10 −18.
Voyager 1 and 2 speed and distance from Sun The Pale Blue Dot image showing Earth from 6 billion kilometres (3.7 billion miles) appearing as a tiny dot (the bluish-white speck approximately halfway down the light band to the right) within the darkness of deep space.