0_Wizard
I love watching the sunset at night, it is the daily disappearance of the Sun below the horizon as a result of Earth's rotation.
Sunset or sundown is the daily disappearance of the Sun below the horizon as a result of Earth's rotation.
chosen_Sunset_0
Sunset
chosen_topic_0_Sunset
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon as a result of Earth's rotation. The Sun will set exactly due west at the equator on the spring and fall equinoxes, each of which occurs only once a year. The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon. Near to the horizon, atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when a sunset is observed. Sunset is distinct from twilight, which has three phases, the first being "civil" twilight, which begins once the Sun has disappeared below the horizon, and continues until it descends to 6 degrees below the horizon; the second phase is "nautical" twilight, between 6 and 12 degrees below the horizon; and the third is "astronomical" twilight, which is the period when the Sun is between 12 and 18 degrees below the horizon.
Archaeoastronomy
Archaeoastronomy (also spelled archeoastronomy) is the study of how people in the past "have understood the phenomena in the sky, how they used these phenomena and what role the sky played in their cultures". Clive Ruggles argues it is misleading to consider archaeoastronomy to be the study of ancient astronomy, as modern astronomy is a scientific discipline, while archaeoastronomy considers symbolically rich cultural interpretations of phenomena in the sky by other cultures. It is often twinned with "ethnoastronomy", the anthropological study of skywatching in contemporary societies. Archaeoastronomy is also closely associated with historical astronomy, the use of historical records of heavenly events to answer astronomical problems and the history of astronomy, which uses written records to evaluate past astronomical practice.
Extraterrestrial skies
In astronomy, an extraterrestrial sky is a view of outer space from the surface of a world other than Earth. The only extraterrestrial sky that has been directly observed and photographed by astronauts is that of the Moon. The skies of Titan, Mars, and Venus have been observed by space probes designed to land on the surface and transmit images back to Earth. Characteristics of extraterrestrial skies appear to vary substantially due to a number of factors. An extraterrestrial atmosphere, if present, has a large bearing on visible characteristics. The atmosphere's density and chemical composition can contribute to differences in colour, opacity (including haze) and the presence of clouds.
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometers, i.e. 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.
Twilight
Twilight on Earth is the illumination of the lower atmosphere when the Sun itself is not directly visible because it is below the horizon. Twilight is produced by sunlight scattering in the upper atmosphere, illuminating the lower atmosphere so that Earth's surface is neither completely lit nor completely dark. The word "twilight" is also used to denote the periods of time when this illumination occurs. The farther the Sun is below the horizon, the dimmer the twilight (other things such as atmospheric conditions being equal). When the Sun reaches 18 degrees below the horizon, the twilight's brightness is nearly zero, and evening twilight becomes nighttime.
Analemma
In astronomy, an analemma (; from Greek "analēmma" "support") is a diagram showing the variation of the position of the Sun in the sky over the course of a year, as viewed at a fixed time of day and from a fixed location on the Earth. The north–south component of the analemma is due to change of the Sun's declination caused by the tilt of the Earth's axis, and the east–west component is due to nonuniform rate of change of the Sun's right ascension, governed by combined effects of axial tilt and Earth's orbital eccentricity. The diagram has the form of a slender figure eight, and can often be found on globes of the Earth.
Orbit of the Moon
The Moon orbits Earth in the prograde direction and completes one revolution relative to the stars in about 27.323 days (a sidereal month) and one revolution relative to the Sun in about 29.530 days (a synodic month). Earth and the Moon orbit about their barycentre (common center of mass), which lies about from Earth's center (about of the radius of Earth). On average, the distance to the Moon is about from Earth's center, which corresponds to about 60 Earth radii. With a mean orbital velocity of , the Moon covers a distance approximately its diameter, or about half a degree on the celestial sphere, each hour.
1_Apprentice
Sunsets are so beautiful! I love watching them, especially at the beach.
0_Wizard
 I find it very relaxing and therapeutic. Near to the horizon, atmospheric refraction causes the rays of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when a sunset is observed.
Near to the horizon, atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when a sunset is observed.
self_Sunset_3
Sunset
self_0_Sunset
Atmospheric refraction
Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. This refraction is due to the velocity of light through air, decreasing (the refractive index increases) with increased density. Atmospheric refraction near the ground produces mirages and can make distant objects appear to shimmer or ripple, elevated or lowered, stretched or shortened, with no mirage involved. The term also applies to the refraction of sound. Atmospheric refraction is considered in measuring the position of both astronomical and terrestrial objects.
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon as a result of Earth's rotation. The Sun will set exactly due west at the equator on the spring and fall equinoxes, each of which occurs only once a year. The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon. Near to the horizon, atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when a sunset is observed. Sunset is distinct from twilight, which has three phases, the first being "civil" twilight, which begins once the Sun has disappeared below the horizon, and continues until it descends to 6 degrees below the horizon; the second phase is "nautical" twilight, between 6 and 12 degrees below the horizon; and the third is "astronomical" twilight, which is the period when the Sun is between 12 and 18 degrees below the horizon.
Optics
Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice.
Atmospheric optics
Atmospheric optics deals with how the unique optical properties of Earth's atmosphere cause a wide range of spectacular optical phenomena. The blue color of the sky is a direct result of Rayleigh scattering, which redirects higher frequency (blue) sunlight back into the field of view of the observer. Because blue light is scattered more easily than red light, the Sun takes on a reddish hue when it is observed through a thick atmosphere, as during a sunrise or sunset. Additional particulate matter in the sky can scatter different colors at different angles, creating colorful, glowing skies at dusk and dawn.
Air mass (astronomy)
In astronomy, air mass (or airmass) is the path length for light from a celestial source to pass through the atmosphere. As it penetrates the atmosphere, light is attenuated by scattering and absorption; the thicker atmosphere through which it passes, the greater the attenuation. Consequently, celestial bodies at the horizon appear less bright than when at the zenith. The attenuation, known as atmospheric extinction, is described quantitatively by the Beer–Lambert–Bouguer law. “Air mass” normally indicates "relative air mass", the path length relative to that at the zenith at sea level so, by definition, the sea-level air mass at the zenith is 1.
Rainbow
A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. Rainbows can be full circles. However, the observer normally sees only an arc formed by illuminated droplets above the ground, and centered on a line from the sun to the observer's eye. In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it.
Mirage of astronomical objects
A mirage of an astronomical object is a naturally occurring optical phenomenon, in which light rays are bent to produce distorted or multiple images of an astronomical object. The mirages might be observed for such astronomical objects as the Sun, the Moon, the planets, bright stars and very bright comets. The most commonly observed are sunset and sunrise mirages. Mirages are distinguished from other refraction phenomena. One of the most prominent features of mirages is that a mirage might only produce images vertically, not sideways, while a simple refraction might distort and bend the images in any way.