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 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