Light-year Light-year The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time. The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in nonspecialist and popular science publications. The unit most commonly used in professional astrometry is the parsec
Unit distance graph way (up to congruence) to place the vertices at distinct locations such that adjacent vertices are a unit distance apart, and this placement also puts the two endpoints of the missing spoke at unit distance . posed the problem of estimating how many pairs of points in a set of "n" points could be at unit distance from each other. In graph theoretic terms, how dense can a unit distance graph be? The hypercube graph provides a lower bound on the number of unit distances proportional to formula_1 By considering points in a square grid with carefully chosen spacing, Erdős