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
Light and air unit and can vary greatly between departments. These multifunctional units are also equipped with diesel generators which supplies electricity to power portable lights and overall scene illumination. This is usually done via a roof mounted telescoping light bank. The unit also has the ability to supply electrical power in an emergency to a shelter, base camp, or medical facility. In the United States, Chapter 24 of National Fire Protection Association regulation 1901 outlines specifications for any air system mounted on firefighting apparatus. Light and air unit A light and air unit, also known as a breathing support unit, is a specialized