Starlight

Starlight is the light emitted by stars. It typically refers to visible electromagnetic radiation from stars other than the Sun, observable from Earth at night, although a component of starlight is observable from Earth during daytime. Sunlight is the term used for the Sun's starlight observed during daytime. During nighttime, albedo describes solar reflections from other Solar System objects, including moonlight, planetshine, and zodiacal light. Observation and measurement of starlight through telescopes is the basis for many fields of astronomy, including photometry and stellar spectroscopy. Hipparchus did not have a telescope or any instrument that could measure apparent brightness accurately, so he simply made estimates with his eyes. He sorted the stars into six brightness categories, which he called magnitudes. He referred to the brightest stars in his catalog as first-magnitudes stars, which were the brightest stars and those so faint he could barely see them were sixth-magnitude stars. Starlight is also a notable part of personal experience and human culture, impacting a diverse range of pursuits including poetry, astronomy, and military strategy. The United States Army spent millions of dollars in the 1950s and onward to develop a starlight scope, that could amplify starlight, moonlight filtered by clouds, and the fluorescence of rotting vegetation about 50,000 times to allow a person to see in the night. In contrast to previously developed active infrared system such as sniperscope, it was a passive device and did not require additional light emission to see. The average color of starlight in the observable universe is a shade of yellowish-white that has been given the name Cosmic Latte. Starlight spectroscopy, examination of the stellar spectra, was pioneered by Joseph Fraunhofer in 1814. Starlight can be understood to be composed of three main spectra types, continuous spectrum, emission spectrum, and absorption spectrum. Starlight illuminance coincides with the human eye's minimum illuminance (~0.