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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. Aurorae light up the skies above the ...
Astronomical coordinate systems. A star 's galactic, ecliptic, and equatorial coordinates, as projected on the celestial sphere. Ecliptic and equatorial coordinates share the March equinox as the primary direction, and galactic coordinates are referred to the galactic center. The origin of coordinates (the "center of the sphere") is ambiguous ...
night sky 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.
The path-line is the combined motion of the planet's orbit (deferent) around Earth and within the orbit itself (epicycle). In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle (from Ancient Greek ἐπίκυκλος (epíkuklos) 'upon the circle', meaning "circle moving on another circle") [ 1 ] was a geometric model ...
Visible-light astronomy has existed as long as people have been looking up at the night sky, although it has since improved in its observational capabilities since the invention of the telescope, which is commonly credited to Hans Lippershey, a German-Dutch spectacle-maker, [1] although Galileo played a large role in the development and ...
Twilight is the time period between dawn and sunrise, or between sunset and dusk. Morning twilight: astronomical, nautical, and civil stages at dawn. The apparent disk of the Sun is shown to scale. [ 1 ] Evening twilight: civil, nautical, and astronomical stages at dusk. The solar disk is shown to scale.
A celestial map by the Dutch cartographer Frederik de Wit, 1670. A star chart is a celestial map of the night sky with astronomical objects laid out on a grid system. They are used to identify and locate constellations, stars, nebulae, galaxies, and planets. [ 1 ] They have been used for human navigation since time immemorial. [ 2 ]
Direction determination refers to the ways in which a cardinal direction or compass point can be determined in navigation and wayfinding.The most direct method is using a compass (magnetic compass or gyrocompass), but indirect methods exist, based on the Sun path (unaided or by using a watch or sundial), the stars, and satellite navigation.