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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 9.46 trillion km or 5.88 trillion mi.
The name describes the galaxy's appearance from the Earth: a hazy band of light visible in the night sky, formed from billions of stars that cannot be individually distinguished by the naked eye. The Milky Way Galaxy has a diameter of 100,000–200,000 light-years and is estimated to contain 100–400 billion stars and at least that number of ...
The nearest known quasar, Markarian 231, is about 581 million light-years from Earth, [129] while others have been discovered as far away as UHZ1, roughly 13.2 billion light-years distant. [ 130 ] [ 131 ] Quasars are noteworthy for providing the first demonstration of the phenomenon that gravity can act as a lens for light .
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 ...
Multiple other interstellar clouds exist in the region within 300 light-years of the Sun, known as the Local Bubble. [262] The latter feature is an hourglass-shaped cavity or superbubble in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of ...
The Milky Way is a barred spiral galaxy with a D 25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years), [10] but only about 1,000 light-years thick at the spiral arms (more at the bulge).
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]
Multiple other interstellar clouds exist in the region within 300 light-years of the Sun, known as the Local Bubble. [160] The latter feature is an hourglass-shaped cavity or superbubble in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of ...