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48-452: Sundown is a synonym for sunset . Sundown may also refer to: Sunset The time of actual sunset is defined in astronomy as two minutes before the upper limb of the Sun disappears below the horizon. Near the horizon, atmospheric refraction causes sunlight rays to be distorted to such an extent that geometrically the solar disk is already about one diameter below the horizon when

96-468: A few days before the spring equinox and extends a few days past the fall equinox). This phenomenon of more daylight than night is not unique to the poles. In fact, at any given time slightly more than half of the earth is in daylight. The 24 hours of summer daylight is known as the midnight sun that is famous in some northern countries. To the north, the Arctic Circle marks this 23.44° boundary. To

144-456: A luminous primary body , such as a local star , also experience daytime, but this article primarily discusses daytime on Earth. Very broadly, most humans tend to be awake during some of the daytime period at their location, and asleep during some of the night period. Approximately half of Earth is illuminated at any time by the Sun . The area subjected to direct illumination is almost exactly half

192-403: A sunset is observed. Sunset is distinct from twilight , which is divided into three stages. The first one is civil twilight , which begins once the Sun has disappeared below the horizon, and continues until it descends to 6 degrees below the horizon. The early to intermediate stages of twilight coincide with predusk . The second phase is nautical twilight , between 6 and 12 degrees below

240-484: Is applied to the x- and y-components of the solar vector presented in Ref. As a ray of white sunlight travels through the atmosphere to an observer, some of the colors are scattered out of the beam by air molecules and airborne particles , changing the final color of the beam the viewer sees. Because the shorter wavelength components, such as blue and green, scatter more strongly, these colors are preferentially removed from

288-410: Is derived from the morpheme "ws" – meaning "up", and "chód" – signifying "move" (from the verb chodzić – meaning "walk, move"), due to the act of the Sun coming up from behind the horizon. The Polish word for west , zachód ( zakhud ), is similar but with the word "za" at the start, meaning "behind", from the act of the Sun going behind the horizon. In Russian , the word for west, запад ( zapad ),

336-407: Is derived from the words за – meaning "behind", and пад – signifying "fall" (from the verb падать – padat' ), due to the act of the Sun falling behind the horizon. In Hebrew, the word for east is 'מזרח', which derives from the word for rising, and the word for west is 'מערב', which derives from the word for setting. The 16th-century astronomer Nicolaus Copernicus was the first to present to

384-442: Is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light (less than 50 nm in diameter). The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlight's wavelengths (> 600 nm) is due to Mie scattering and is not strongly wavelength-dependent. Mie scattering is responsible for the light scattered by clouds, and also for

432-408: Is instead lofted into the stratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors called afterglows and pre-sunrise glows. A number of eruptions, including those of Mount Pinatubo in 1991 and Krakatoa in 1883 , have produced sufficiently high stratus clouds containing sulfuric acid to yield remarkable sunset afterglows (and pre-sunrise glows) around

480-449: Is the period of the day during which a given location experiences natural illumination from direct sunlight . Daytime occurs when the Sun appears above the local horizon , that is, anywhere on the globe's hemisphere facing the Sun. In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. Other planets and natural satellites that rotate relative to

528-499: The Antarctic Circle experience no full sunset or sunrise on at least one day of the year, when the polar day or the polar night persists continuously for 24 hours. At latitudes greater than within half a degree of either pole, the sun cannot rise or set on the same date on any day of the year, since the sun's angular elevation between solar noon and midnight is less than one degree. The time of sunset varies throughout

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576-540: The Equator remains warm throughout the year, with only 12 hours of daylight per day. Although the daytime length at the Equator remains 12 hours in all seasons, the duration at all other latitudes varies with the seasons. During the winter, daytime lasts shorter than 12 hours; during the summer, it lasts longer than 12 hours. Northern winter and southern summer concur, while northern summer and southern winter concur. At

624-576: The Equator , the daytime period always lasts about 12 hours, regardless of season. As viewed from the Equator, the Sun always rises and sets roughly vertically, following an apparent path close to perpendicular to the horizon . From the March equinox to the September equinox , the Sun rises within 23.44° north of due east, and sets within 23.44° north of due west. From the September equinox to

672-438: The zenith , passing directly overhead at solar noon . The fact that the equatorial Sun is always so close to the zenith at solar noon explains why the tropical zone contains the warmest regions on the planet overall. Additionally, the Equator sees the shortest sunrise or sunset because the Sun's path across the sky is so nearly perpendicular to the horizon. On the equinoxes, the solar disk takes only two minutes to traverse

720-579: The Earth, rather than a point source of light, sunrise and sunset are not instantaneous and the exact definition of both can vary with context. Additionally, the Earth's atmosphere further bends and diffuses light from the Sun and lengthens the period of sunrise and sunset. For a certain period after sunset and before sunrise, indirect light from the Sun lightens the sky on Earth; this period is often referred to as twilight . Certain groups, such as Earthly astronomers, do not consider daytime to be truly ended until

768-454: The March equinox, the Sun rises within 23.44° south of due east and sets within 23.44° south of due west. The Sun's path lies entirely in the northern half of the celestial sphere from the March equinox to the September equinox, but lies entirely in the southern half of the celestial sphere from the September equinox to the March equinox. On the equinoxes, the equatorial Sun culminates at

816-425: The Sun's disc is actually well below the Earth's horizon, because of this indirect illumination. Daytime length or daytime duration is the time elapsed between beginning and end of the daytime period. Given that Earth's own axis of rotation is tilted 23.44° to the line perpendicular to its orbital plane , called the ecliptic , the length of daytime varies with the seasons on the planet's surface, depending on

864-448: The Sun's non-zero size, whenever and wherever sunset occurs, it is always in the northwest quadrant from the March equinox to the September equinox , and in the southwest quadrant from the September equinox to the March equinox. Sunsets occur almost exactly due west on the equinoxes for all viewers on Earth. Exact calculations of the azimuths of sunset on other dates are complex, but they can be estimated with reasonable accuracy by using

912-430: The air is full of red dust , blown into the atmosphere by high winds, so its sky color is mainly determined by a Mie Scattering process, resulting in more blue hues than an Earth sunset. One study also reported that Martian dust high in the atmosphere can reflect sunlight up to two hours after the Sun has set, casting a diffuse glow across the surface of Mars. Daytime Daytime or day as observed on Earth

960-409: The analemma. As sunrise and sunset are calculated from the leading and trailing edges of the Sun, respectively, and not the center, the duration of a daytime is slightly longer than nighttime (by about 10 minutes, as seen from temperate latitudes). Further, because the light from the Sun is refracted as it passes through the Earth's atmosphere, the Sun is still visible after it is geometrically below

1008-589: The apparent height of the solar disk. Its width is unaltered, so the disk appears wider than it is high. (In reality, the Sun is almost exactly spherical.) The Sun also appears larger on the horizon, an optical illusion, similar to the moon illusion . Locations within the Arctic and Antarctic Circles experience periods where the Sun does not rise or set for 24 hours or more, known as polar day and polar night . These phenomena occur due to Earth’s axial tilt , causing continuous sunlight or darkness at certain times of

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1056-415: The beam. At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely, leaving the longer wavelength orange and red hues we see at those times. The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the shorter wavelengths of light

1104-436: The compass bear names etymologically derived from words for sunrise and sunset. The English words " orient " and " occident ", meaning "east" and "west", respectively, are descended from Latin words meaning "sunrise" and "sunset". The word "levant", related e.g. to French " (se) lever " meaning "lift" or "rise" (and also to English "elevate"), is also used to describe the east. In Polish , the word for east wschód ( vskhud ),

1152-516: The corresponding solstice. At latitudes closer to the Equator and on the Equator itself, it will be overhead twice per year (on the equinoxes in the case of the Equator), leading to the Lahaina Noon or zero shadow day phenomenon. Outside the tropics, the Sun never passes directly overhead. Around the poles, which coincide with the rotational axis of Earth as it passes through the surface,

1200-552: The days get longer and sunsets occur later every day until the day of the latest sunset, which occurs after the summer solstice. In the Northern Hemisphere , the latest sunset occurs late in June or in early July, but not on the summer solstice of June 21. This date depends on the viewer's latitude (connected with the Earth's slower movement around the aphelion around July 4). Likewise, the earliest sunset does not occur on

1248-431: The daytime halo of white light around the Sun (forward scattering of white light). Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air. Sometimes just before sunrise or after sunset a green flash can be seen. Ash from volcanic eruptions, trapped within the troposphere , tends to mute sunset and sunrise colors, while volcanic ejecta that

1296-481: The horizon (from top to bottom at sunrise and from bottom to top at sunset). The tropics occupy a zone of Earth's surface between 23.44° north and 23.44° south of the Equator . Within this zone, the Sun will pass almost directly overhead (or culminate ) on at least one day per year. The line of 23.44° north latitude is called the Tropic of Cancer , because when it was named, the Sun passed overhead at this location at

1344-439: The horizon as winter approaches, and gradually rises above it as summer approaches. At the poles, apparent sunrise and sunset may last for several days. At middle latitudes , far from both the Equator and the poles, variations in the length of daytime are moderate. In the higher middle latitudes where Montreal , Paris and Ushuaia are located, the difference in the length of the day from summer to winter can be very noticeable:

1392-414: The horizon, even in summer, which is one of reasons why these regions of the world are consistently cold in all seasons (others include the effect of albedo , the relative increased reflection of solar radiation of snow and ice). Even at the summer solstice, when the Sun reaches its highest point above the horizon at noon, it is still only 23.44° above the horizon at the poles. Additionally, as one approaches

1440-400: The horizon. Refraction also affects the apparent shape of the Sun when it is very close to the horizon. It makes things appear higher in the sky than they really are. Light from the bottom edge of the Sun's disk is refracted more than light from the top, since refraction increases as the angle of elevation decreases. This raises the apparent position of the bottom edge more than the top, reducing

1488-436: The horizon. The third phase is astronomical twilight , which is the period when the Sun is between 12 and 18 degrees below the horizon. Dusk is at the very end of astronomical twilight, and is the darkest moment of twilight just before night . Finally, night occurs when the Sun reaches 18 degrees below the horizon and no longer illuminates the sky. Locations further north than the Arctic Circle and further south than

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1536-412: The latest sunsets occurring some time after December 21 in summer, again depending on one's southern latitude. For a few weeks surrounding both solstices, both sunrise and sunset get slightly later each day. Even on the equator, sunrise and sunset shift several minutes back and forth through the year, along with solar noon. These effects are plotted by an analemma . Neglecting atmospheric refraction and

1584-401: The observer's latitude . Areas tilted toward the Sun are experiencing summer . Their tilt toward the Sun leads to more than half of the day seeing daylight and warmer temperatures, due to the higher directness of solar rays, the longer period of daytime itself, and less absorption of sunlight in the atmosphere . While increased daylight can have some effect on the higher temperatures in

1632-423: The plane of its orbit around the Sun (which is parallel with the direction of sunlight), and so the length of the daytime period varies from one point on the planet to another. Additionally, since the axis of rotation is relatively fixed in comparison to the stars, it moves with respect to the Sun as the planet orbits the star. This creates seasonal variations in the length of the daytime period at most points on

1680-408: The planet's surface. The period of daytime from the standpoint of a surface observer is roughly defined as the period between sunrise , when the Earth's rotation towards the east first causes the Sun's disc to appear above the horizon, to sunset , when the continuing rotation of the Earth causes the Sun's disc to disappear below the horizon to the west. Because the Sun is a luminous disc as seen from

1728-412: The planet; but because of atmospheric and other effects that extend the reach of indirect illumination, the area of the planet covered by either direct or indirect illumination amounts to slightly more than half the surface. The hemisphere of Earth experiencing daytime at any given instant changes continuously as the planet rotates on its own axis. The axis of the Earth's rotation is not perpendicular to

1776-415: The poles the apparent path of the Sun through the sky each day diverges increasingly from the vertical. As summer approaches, the Sun rises and sets become more northerly in the north and more southerly in the south. At the poles, the path of the Sun is indeed a circle, which is roughly equidistant above the horizon for the entire duration of the daytime period on any given day. The circle gradually sinks below

1824-404: The seasonal variations in the length of daytime are extreme. In fact, within 23.44° latitude of the poles, there will be at least some days each year during which the sun never goes below the horizon. There will also be days when the Sun never rises above the horizon. This number will be fewer, but close to the number of days in the summer where the sun doesn't set (for example the sunrise is usually

1872-489: The size it does from Earth , due to the greater distance between Mars and the Sun. The colors are typically hues of blue, but some Martian sunsets last significantly longer and appear far redder than is typical on Earth. The colors of the Martian sunset differ from those on Earth. Mars has a thin atmosphere , lacking oxygen and nitrogen , so the light scattering is not dominated by a Rayleigh Scattering process. Instead,

1920-417: The sky may still be lit at 10 pm in summer, but may be dark at 5 pm in winter. In the lower middle latitudes where southern California , Egypt and South Africa are located, the seasonal difference is smaller, but still results in approximately 4 hours difference in daylight between the winter and summer solstices. The difference becomes less pronounced the closer one gets to the equator. An approximation to

1968-400: The south, the Antarctic Circle marks the boundary. These boundaries correspond to 66.56° north or south latitude, respectively. Because the sky is still bright and stars can't be seen when the sun is less than 6 degrees under the horizon, 24-hour nights with stars visible all the time only happen beyond 72°34' north or south latitude. At and near the poles, the Sun never rises very high above

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2016-504: The summer, most of temperature rise results from the directness of the Sun, not the increased daylight. The high angles (around the zenith ) of the Sun causes the tropics to be warm, while low angles (barely above the horizon) causes the polar regions to be cold. The slight effect of daylight hours on average seasonal temperature can be seen with the poles and tropical regions. The poles are still cold during their respective summers, despite seeing 24 hours of daylight for six months, while

2064-483: The time of year when it was near the constellation of Cancer. The equivalent line of south latitude is called the Tropic of Capricorn , for similar reasons. The sun enters and leaves each zodiacal constellation slightly later each year at the rate of about 1 day every 72 years. For more information, see precession of the equinoxes . On the Tropical Circles, the Sun is directly overhead only once per year, on

2112-596: The winter solstice, but rather about two weeks earlier, again depending on the viewer's latitude. In the Northern Hemisphere, it occurs in early December or late November (influenced by the Earth's faster movement near its perihelion , which occurs around January 3). Likewise, the same phenomenon exists in the Southern Hemisphere , but with the respective dates reversed, with the earliest sunsets occurring some time before June 21 in winter, and

2160-438: The world a detailed and eventually widely accepted mathematical model supporting the premise that the Earth is moving and the Sun actually stays still, despite the impression from our point of view of a moving Sun. Sunsets on other planets appear different because of differences in the distance of the planet from the Sun and non-existent or differing atmospheric compositions. On Mars , the setting Sun appears about two-thirds

2208-442: The world. The high-altitude clouds serve to reflect strongly reddened sunlight still striking the stratosphere after sunset, down to the surface. Some of the most varied colors at sunset can be found in the opposite or eastern sky after the Sun has set during twilight. Depending on weather conditions and the types of clouds present, these colors have a wide spectrum, and can produce unusual results. In some languages, points of

2256-441: The year and is determined by the viewer's position on Earth, specified by latitude and longitude , altitude , and time zone . Small daily changes and noticeable semi-annual changes in the timing of sunsets are driven by the axial tilt of the Earth , daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other. During winter and spring,

2304-469: The year. Approximate locations of sunset on the horizon ( azimuth ) as described above can be found in Refs. The figure on the right is calculated using the solar geometry routine as follows: An interesting feature in the figure on the right is apparent hemispheric symmetry in regions where daily sunrise and sunset actually occur. This symmetry becomes clear if the hemispheric relation in sunrise equation

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