Speed of light they appeared 13 billion years ago, when the universe was less than a billion years old. The fact that more distant objects appear to be younger, due to the finite speed of light, allows astronomers to infer the evolution of stars, of galaxies, and of the universe itself. Astronomical distances are sometimes expressed in light-years, especially in popular science publications and media. A light-year is the distance light travels in one 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,
Light and air unit Light and air unit A light and air unit, also known as a breathing support unit, is a specialized piece of firefighting apparatus used by firefighters to provide supplemental lighting and SCBA air bottles at the scene of an emergency. During prolonged emergencies, particularly structure fires, where firefighters must remain on air (wearing their SCBAs), these air bottles will need to be replaced and refilled. The light and air unit has the ability to refill the SCBA bottles while in the field using onboard air compressors. It also carries a supply of spare air cylinders. These units are highly customizable