Dawn
Encyclopedia
Twilight
Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below...
before sunrise
Sunrise
Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the point at which the sky begins to lighten, some time before the sun itself appears, ending twilight...
. It is recognized by the presence of weak sunlight, while the sun itself is still below the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
. Dawn should not be confused with sunrise, which is the moment when the leading edge of the sun itself appears above the horizon.
The duration of the twilight period between dawn and sunrise varies greatly depending on the observer's latitude, from a few minutes in equatorial regions
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
to many hours in polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
s. Dawn may easily be determined by observing a thread. When the color of a thread can be determined, changing from black to the thread's distinctive color, the 'crack of dawn' has occurred. This same measure of ambient light can be used to determine, conversely, the instant of dusk
Dusk
Dusk is the beginning of darkness in the evening, and occurs after twilight, when the sky generally remains bright and blue. Civil dusk is when the earth has rotated enough that the center of the sun is at 6° below the local horizon...
.
Technical definitions
There are also more technical definitions of dawn, including the following:Astronomical dawn : the moment after which the sky is no longer completely dark; formally defined as the time at which the sun is 18 degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
s below the horizon in the morning
Morning
The word morning originally referred to the sunrise. Morning precedes midday, afternoon, and night in the sequence of a day.Morning is the part of the day usually reckoned from dawn to noon...
.
Nautical dawn: the time at which there is enough sunlight for the horizon and some objects to be distinguishable; formally, when the sun is 12 degrees below the horizon in the morning.
Civil dawn : that time at which there is enough light for objects to be distinguishable, so that outdoor activities can commence; formally, when the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
is 6 degrees below the horizon in the morning.
Solar dawn : that time at which the leading edge of the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
reaches the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
in the morning, ignoring the effect of atmospheric refraction
Atmospheric refraction
Atmospheric refraction is the deviation of light or other things like humanelectromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude...
.
Causes and effects
During dawn (and dusk) it is usually possible (provided that the sky is cloud-free) to see approximately in which direction the sun is (though it's below the horizon).Though it is possible to localize the direction of the sun during astronomical dawn and dusk, people in general experience astronomical dawn and dusk as night, even without clouds. Zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
is dark and more than just the brightest shining stars can be seen (except low above the horizon in the direction of the sun).
At civil dawn there is no darkness in any direction, nor at zenith. The sky is bright, even when cloudy. In mid and northern Scandinavia, summer nights never get any further than to civil dusk or dawn. This period of "bright nights" is longer at higher latitudes (further north).
North of the polar circle
Polar circle
A polar circle is either the Arctic Circle or the Antarctic Circle. On Earth, the Arctic Circle is located at a latitude of N, and the Antarctic Circle is located at a latitude of S....
(at 66°30′ N) the sun does not set at all at the summer solstice
Summer solstice
The summer solstice occurs exactly when the axial tilt of a planet's semi-axis in a given hemisphere is most inclined towards the star that it orbits. Earth's maximum axial tilt to our star, the Sun, during a solstice is 23° 26'. Though the summer solstice is an instant in time, the term is also...
. The period of no sunset
Sunset
Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west...
is longer closer to the North Pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
. The angular radius of the polar circle is equal to the angle between the plane of Earth's equator and that of the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
. At true solar noon
Noon
Noon is usually defined as 12 o'clock in the daytime. The word noon is also used informally to mean midday regarding the location of the sun not the middle of a persons day. Although this is a time around the middle of the day when people in many countries take a lunch break...
at London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
(latitude 51°30′ N), the sun is at an angle of (90 - 51,5 =) 38.5 degrees above the horizon at the equinoxes. At winter solstice the "sun height" (solar elevation angle
Solar elevation angle
The solar elevation angle is the elevation angle of the sun. That is, the angle between the directionof the geometric center of the sun's apparent disk and the horizon...
) is (38.5 - 23.5 =) 15.0 degrees above horizon. At summer solstice the "sun height" is instead (38.5 + 23.5 =) 62 degrees above horizon.
Nautical dawn is more difficult to describe. Near the summer solstice, latitudes higher than 54°30′ get no darker than nautical dawn/dusk; the "darkness of the night" varies greatly in these latitudes.
But while, for instance, Glasgow, Scotland at 56°00′ N and Copenhagen, Denmark at 55°45′ N get a few hours of "night feeling", Oslo, Norway at 60°00′ N and Stockholm, Sweden at 59°20′ N seems very bright all the time the sun is below the horizon. This may call for a different classification of dawn and dusk terminology for more practical use than astronomy. When the sun
gets 9.0 to 9.5 degrees below the horizon (at summer solstice this is at latitudes 57°30′–57°00′), zenith gets dark even on cloud-free nights (if there is no full moon); more than just the brightest shining stars are clearly visible in a large majority of the sky.
All phases of dawn and dusk are shortest at the equator, where the sun at equinox rises and sets at a right angle to the horizon. Civil, nautical, and astronomical dawn and dusk last only 24 minutes each.
Dawn and dusk times are fastest at the times around the equinoxes and slowest at summer and winter solstices on all places on the earth.
At the poles, the sun rises at the spring equinox and sets at the autumn equinox, with a long period of dawn/dusk, lasting for a few weeks .
Mythology
Many Indo-European mythologiesProto-Indo-European religion
Proto-Indo-European religion is the hypothesized religion of the Proto-Indo-European peoples based on the existence of similarities among the deities, religious practices and mythologies of the Indo-European peoples. Reconstruction of the hypotheses below is based on linguistic evidence using the...
have a goddess
Goddess
A goddess is a female deity. In some cultures goddesses are associated with Earth, motherhood, love, and the household. In other cultures, goddesses also rule over war, death, and destruction as well as healing....
of dawn, separate from the male Solar deity
Solar deity
A solar deity is a sky deity who represents the Sun, or an aspect of it, usually by its perceived power and strength. Solar deities and sun worship can be found throughout most of recorded history in various forms...
, her name deriving from PIE
Pie
A pie is a baked dish which is usually made of a pastry dough casing that covers or completely contains a filling of various sweet or savoury ingredients....
*h2ausos-
Hausos
One of the most important goddesses of reconstructed Proto-Indo-European religion is the dawn goddess. Her name is reconstructed as Ausōs , besides numerous epithets....
, derivations of which include Greek Eos
Eos
In Greek mythology, Eos is the Titan goddess of the dawn, who rose from her home at the edge of Oceanus, the ocean that surrounds the world, to herald her brother Helios, the Sun.- Greek literature :...
, Roman Aurora
Aurora (mythology)
Aurora is the Latin word for dawn, the goddess of dawn in Roman mythology and Latin poetry.Like Greek Eos and Rigvedic Ushas , Aurora continues the name of an earlier Indo-European dawn goddess, *Hausos....
, Indian Ushas
Ushas
Ushas , Sanskrit for "dawn", is a Vedic deity, and consequently a Hindu deity as well.Sanskrit is an s-stem, i.e. the genitive case is . It is from PIE , cognate to Greek Eos and Latin Aurora....
, Slavic Zornitsa and possibly a Germanic *Austrōn-
Eostre
Old English Ēostre and Old High German Ôstarâ are the names of a Germanic goddess whose Anglo-Saxon month, Ēostur-monath , has given its name to the festival of Easter...
(whence Easter
Easter
Easter is the central feast in the Christian liturgical year. According to the Canonical gospels, Jesus rose from the dead on the third day after his crucifixion. His resurrection is celebrated on Easter Day or Easter Sunday...
). The Hindu
Hinduism
Hinduism is the predominant and indigenous religious tradition of the Indian Subcontinent. Hinduism is known to its followers as , amongst many other expressions...
dawn deity Aruṇa
Aruna
In to Hindu mythology and Hindu scriptures, Aruṇá or Aruṇ is a personification of the reddish glow of the rising Sun, which is believed to have spiritual powers...
is male. In Native American mythology
Native American mythology
Native American mythology is the body of traditional narratives associated with Native American religion from a mythographical perspective. Native American belief systems include many sacred narratives. Such spiritual stories are deeply based in Nature and are rich with the symbolism of seasons,...
, Anpao
Anpao
In Lakota mythology , Anpao is an entity with two faces that represents the spirit of the dawn....
is an entity with two faces.
Religion
In IslamIslam
Islam . The most common are and . : Arabic pronunciation varies regionally. The first vowel ranges from ~~. The second vowel ranges from ~~~...
, dawn (Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...
fajr) is the time of the first prayer of the day, and the beginning of the daily fast
Fasting
Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...
during Ramadan
Ramadan
Ramadan is the ninth month of the Islamic calendar, which lasts 29 or 30 days. It is the Islamic month of fasting, in which participating Muslims refrain from eating, drinking, smoking and sex during daylight hours and is intended to teach Muslims about patience, spirituality, humility and...
.