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The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground ...
ICRF – (astrophysics terminology) International Celestial Reference Frame, a coordinate system based on radio sources used to define the locations of objects in the sky; ICRS – (astrophysics terminology) International Celestial Reference System, a coordinate system based on Hipparcos observations used to define the locations of objects in ...
The appearance of the Earth's sky at nighttime, when the Sun is below the horizon, and more specifically when clear weather and low levels of ambient light permit visibility of celestial objects such as stars, planets, and the Moon. The night sky remains a fundamental setting for both amateur and professional observational astronomy. non ...
The New General Catalogue of Nebulae and Clusters of Stars (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and emission nebulae.
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include moonlight , starlight , and airglow , depending on location and timing.
Sky conditions are estimated in terms of how many eighths of the sky are covered in cloud, ranging from 0 oktas (completely clear sky) through to 8 oktas (completely overcast). In addition, in the SYNOP code there is an extra cloud cover indicator '9' indicating that the sky is totally obscured (i.e. hidden from view), usually due to dense fog ...
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A large number of black holes are designated by their position in the sky and prefixed with the instrument or survey that discovered them. [15] Examples are SDSS J0100+2802 (where SDSS stands for Sloan Digital Sky Survey), and RX J1131−1231, observed by the Chandra X-ray Observatory. [16]