It takes approximately 8.31 minutes for light to travel this distance. One astronomical unit (the distance from the Sun to the Earth). (The moon is roughly 384400 kilometers from Earth, on average. Reflected sunlight from the Moon's surface takes 1.2-1.3 seconds to travel the distance to the Earth's surface. List of orders of magnitude for length Factor ( ly) Gigalight-years are typically used to measure distances to supergalactic structures, such as clusters of quasars or the Great Wall. One gigalight-year is about 306.6 million parsecs. One gigalight-year, abbreviation "Gly", is one billion light-years - one of the largest distance measures used. Megalight-years are typically used to measure distances between neighboring galaxies and galaxy clusters. One megalight-year, abbreviated "Mly", is one million light-years, or about 306,600 parsecs. Kilolight-years are typically used to measure distances between parts of a galaxy. One kilolight-year, abbreviated "kly", is one thousand light-years, or about 307 parsecs. Yahoo's light-year definition works out to a year length of ~365.2411 days.ĭistances measured in fractions of a light-year usually involve objects within a star system.ĭistances measured in light-years include distances between nearby stars, such as those in the same spiral arm or globular cluster. Google uses a light-year based on the 1900 mean tropical year. Internet search engines use various definitions. The IAU uses a Julian year of 365.25 days, while other sources may use a Gregorian year of 365.2425 days, or another year altogether. The exact length of a light year depends on the exact length used for one “Earth year”. However, outside scientific circles, the term light-year is more widely used. The parsec is preferred because it can be more easily derived from, and compared with, observational data. This is equal to approximately 3.26 light-years. In astronomy, the preferred unit of measurement for such distances is the parsec, which is defined as the distance at which an object will generate one arcsecond of parallax when the observing object moved one astronomical unit perpendicular to the line of sight to the observer. The light-year is often used to measure distances to stars. The IAU Style Manual recommends the use of Julian calendar years (not Gregorian) of 365.25 days, or exactly 31,557,600 seconds. Yahoo's and Google's calculators use a smaller value than the IAU), thus the light-year is not an appropriate unit to use when extremely high precision is required. However, other reference years are often used (e.g. This is the value recommended by the IAU. The figures above are based on a reference year of exactly 365.25 days (each of exactly 86,400 SI seconds). The exact length of the light-year depends on the length of the reference year used in the calculation, and there is no wide consensus on the reference to be used.
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