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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.
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]
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 scope of the Solar System and is about 3.26 light-years: 1 pc = 1 au/tan(1″) [6] [61] Proxima Centauri: 268 000 ...
On this scale, the distance to Alpha Centauri A would be 276 kilometers (171 miles). The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/390 of a light-year in 46 years and is currently moving at 1/17,600 the speed of light. At this rate, a journey to Proxima Centauri would take 75,000 years.
The speed of light in IAU is the defined value c 0 = 299 792 458 m/s of the SI units. In terms of this speed, the old definition of the astronomical unit of length had the accepted value: [ 3 ] 1 au = c 0 τ A = ( 149 597 870 700 ± 3 ) m, where τ A is the transit time of light across the astronomical unit.
The first test of two-way laser communication occurred in December 2021 when NASA’s Laser Communications Relay Demonstration launched and went into orbit about 22,000 miles (35,406 kilometers ...
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).
While the “Epoch of Reionization” sounds like the title of a sci-fi novel destined for a Hugo award, this very real era of the universe featured the first light from the very first stars.