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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 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 scope of the Solar ...
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).
This number is likely much higher, due to the sheer number of stars needed to be surveyed; a star approaching the Solar System 10 million years ago, moving at a typical Sun-relative 20–200 kilometers per second, would be 600–6,000 light-years from the Sun at present day, with millions of stars closer to the Sun.
3.1 Em – 310 light-years – distance to Canopus according to Hipparcos [203] 3.9 Em – 410 light-years – distance to Betelgeuse according to Hipparcos [204] 6.2 Em – 650 light-years – distance to the Helix Nebula, located in the constellation Aquarius [205] 8.2 Em – 860 light-years – distance to Rigel according to Hipparcos [203]
Light in a vacuum travels around 300,000 kilometres (186,000 mi) per second, so 1 light-year is about 9.461 × 10 12 kilometers (5.879 trillion miles) or 63,241 AU. Hence, Proxima Centauri is approximately 4.243 light-years from Earth.
The result was a measured radius of 696,342 ± 65 kilometres (432,687 ± 40 miles). [4] Haberreiter, Schmutz & Kosovichev (2008) [1] determined the radius corresponding to the solar photosphere to be 695,660 ± 140 kilometres (432,263 ± 87 miles). This new value is consistent with helioseismic estimates; the same study showed that previous ...