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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.
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 ...
For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
where θ is the measured angle in arcseconds, Distance earth-sun is a constant (1 au or 1.5813 × 10 −5 ly). The calculated stellar distance will be in the same measurement unit as used in Distance earth-sun (e.g. if Distance earth-sun = 1 au , unit for Distance star is in astronomical units; if Distance earth-sun = 1.5813 × 10 −5 ly, unit ...
Earth radius R 🜨 ≈ 6,371 km [14] Lunar distance LD ≈ 384 402 km. [15] Average distance between the center of Earth and the center of the Moon. astronomical unit au. Defined as 149 597 870 700 m. [16] Approximately the distance between the Earth and Sun. light-year ly ≈ 9 460 730 472 580.8 km.
The Hubble constant is most frequently quoted in km/s/Mpc, which gives the speed of a galaxy 1 megaparsec (3.09 × 10 19 km) away as 70 km/s. Simplifying the units of the generalized form reveals that H 0 specifies a frequency (SI unit: s −1), leading the reciprocal of H 0 to be known as the Hubble time (14.4 billion years). The Hubble ...
Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is ...
10.16 cm = 1.016 dm – 1 hand used in measuring height of horses (4 inches) 12 cm = 1.2 dm – diameter of a compact disc (CD) (= 120 mm) 15 cm = 1.5 dm – length of a Bic pen with cap on; 22 cm = 2.2 dm – diameter of a typical association football (soccer ball) 30 cm = 3 dm – typical school-use ruler length (= 300 mm)