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,
Mercer 3 Mercer 3 Mercer 3 is a heavily obscured globular cluster embedded in the disk of the Milky Way galaxy. It was discovered in 2008 in the data obtained by 2MASS and GLIMPSE infrared surveys. The cluster is located in the Scutum constellation. It had avoided detection for such a long time due to the extremely strong foreground extinction in its direction reaching 24 magnitudes in the visible light. Mercer 3 is probably situated at the distance from 4 to 8 kpc from the Sun and has a half-light radius of 0.7–1.5 pc. Mercer 3 is an old globular cluster having