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A light-year, alternatively spelled light year (ly or lyr [3]), is a unit of length used to express astronomical distances and is equal to exactly 9 460 730 472 580.8 km, which is approximately 5.88 trillion mi.
Light-year: 63 241 — Distance light travels in one Julian year (365.25 days) — Oort cloud: 75 000: ± 25 000: Distance of the outer limit of Oort cloud from the Sun (estimated, corresponds to 1.2 light-years) — Parsec: 206 265 — One parsec. The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the ...
The x-axis is distance, in billions of light years; the y-axis is time, in billions of years since the Big Bang. This is the same model as in the earlier figure, with dark energy and an event horizon. Cosmological time is identical to locally measured time for an observer at a fixed comoving spatial position, that is, in the local comoving ...
This distance is the time that it took light to reach the observer from the object multiplied by the speed of light. For instance, the radius of the observable universe in this distance measure becomes the age of the universe multiplied by the speed of light (1 light year/year), which turns out to be approximately 13.8 billion light years.
The astronomical unit of length is now defined as exactly 149 597 870 700 meters. [4] It is approximately equal to the mean Earth–Sun distance. It was formerly defined as that length for which the Gaussian gravitational constant (k) takes the value 0.017 202 098 95 when the units of measurement are the astronomical units of length, mass and ...
590 Ym – 62 billion light-years – cosmological event horizon: the largest comoving distance from which light will ever reach us (the observer) at any time in the future 886.48 Ym – 93.7 billion light-years – the diameter of the observable universe (twice the particle horizon ); however, there might be unobserved distances that are even ...
The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. [2] Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy ...
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. [89]