Dawn

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Late summer dawn over the Mojave Desert, California Desert Dawn.jpg
Late summer dawn over the Mojave Desert, California
Dawn is sometimes considered the beginning of morning twilight, sometimes the period of twilight, and sometimes the time of sunrise. Twilight description full day.svg
Dawn is sometimes considered the beginning of morning twilight, sometimes the period of twilight, and sometimes the time of sunrise.

Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizon. [1] This morning twilight period will last until sunrise (when the Sun's upper limb breaks the horizon), when direct sunlight outshines the diffused light.

Contents

Civil, nautical, and astronomical dawn, when defined as the beginning time of the corresponding twilight Twilight-dawn subcategories.svg
Civil, nautical, and astronomical dawn, when defined as the beginning time of the corresponding twilight

Etymology

"Dawn" derives from the Old English verb dagian, "to become day".

Types of dawn

Dawn begins with the first sight of lightness in the morning, and continues until the Sun breaks the horizon. This morning twilight before sunrise is divided into three categories depending on the amount of sunlight that is present in the sky, which is determined by the angular distance of the centre of the Sun (degrees below the horizon) in the morning. These categories are astronomical, nautical, and civil dawn.[ citation needed ]

Astronomical dawn

Dawn at La Silla Observatory, Chile New Dawn at La Silla.jpg
Dawn at La Silla Observatory, Chile

Astronomical dawn begins when the Sun is 18 degrees below the horizon in the morning. Astronomical twilight follows instantly until the Sun is 12 degrees below the horizon. [4] At this point a very small portion of the Sun's rays illuminate the sky and the fainter stars begin to disappear. Astronomical dawn is often indistinguishable from night, especially in areas with light pollution. Astronomical dawn marks the beginning of astronomical twilight, which lasts until nautical dawn. [5]

Nautical dawn

Nautical twilight begins when there is enough illumination for sailors to distinguish the horizon at sea but the sky being too dark to perform outdoor activities. Formally, it begins when the Sun is 12 degrees below the horizon in the morning. The sky becomes light enough to clearly distinguish it from land and water. Nautical dawn marks the start of nautical twilight, which lasts until civil dawn. [5] [4]

Civil dawn

Serra dos Orgaos National Park, in Rio de Janeiro state, Brazil, at dawn Amanhecer nos Portais.jpg
Serra dos Órgãos National Park, in Rio de Janeiro state, Brazil, at dawn

Civil dawn begins when there is enough light for most objects to be distinguishable, so that some outdoor activities can commence. Formally, it occurs when the Sun is 6 degrees below the horizon in the morning. [4]

If the sky is clear, it is blue colored, and if there is some cloud or haze, there can be bronze, orange and yellow colours. Some bright stars and planets such as Venus and Jupiter are visible to the naked eye at civil dawn. This moment marks the start of civil twilight, which lasts until sunrise. [5]

Effects of latitude

The duration of the twilight period (e.g. between astronomical dawn and sunrise) varies greatly depending on the observer's latitude: from a little over 70 minutes at the Equator, to many hours in the polar regions.[ citation needed ]

The Equator

The period of twilight is shortest at the Equator, where the equinox Sun rises due east and sets due west, at a right angle to the horizon. Each stage of twilight (civil, nautical, and astronomical) lasts only 24 minutes. From anywhere on Earth, the twilight period is shortest around the equinoxes and longest on the solstices.[ citation needed ]

Polar regions

Daytime becomes longer as the summer solstice approaches, while nighttime gets longer as the winter solstice approaches. This can have a potential impact on the times and durations of dawn and dusk. This effect is more pronounced closer to the poles, where the Sun rises at the vernal equinox and sets at the autumn equinox, with a long period of twilight, lasting for a few weeks.[ citation needed ]

The polar circle (at 66°34 north or south) is defined as the lowest latitude at which the Sun does not set at the summer solstice. Therefore, the angular radius of the polar circle is equal to the angle between Earth's equatorial plane and the ecliptic plane. This period of time with no sunset lengthens closer to the pole.[ citation needed ]

Near the summer solstice, latitudes higher than 54°34 get no darker than nautical twilight; the "darkness of the night" varies greatly at these latitudes.[ citation needed ]

At latitudes higher than about 60°34, summer nights get no darker than civil twilight. This period of "bright nights" is longer at higher latitudes.[ citation needed ]

Example

Around the summer solstice, Glasgow, Scotland at 55°51′ N, and Copenhagen, Denmark at 55°40′ N, get a few hours of "night feeling". Oslo, Norway at 59°56′ N, and Stockholm, Sweden at 59°19′ N, seem very bright when the Sun is below the horizon. When the Sun gets 9.0 to 9.5 degrees below the horizon (at summer solstice this is at latitudes 57°30′–57°00′), the zenith gets dark even on cloud-free nights (if there is no full moon), and the brightest stars are clearly visible in a large majority of the sky.[ citation needed ]

Mythology and religion

In Islam, Zodiacal Light (or "false dawn") is referred to as False Morning (Subhe-Kazeb, Persian صبح کاذب) and astronomical dawn is called Sahar (سحر) or True Morning (Subhe-Sadeq, Persian صبح صادق), and it is the time of first prayer of the day, and the beginning of the daily fast during Ramadan. [6]

Many Indo-European mythologies have a dawn goddess, separate from the male Solar deity, her name deriving from PIE *h2ausos- , derivations of which include Greek Eos, Roman Aurora and Indian Ushas. Also related is Lithuanian Aušrinė, and possibly a Germanic *Austrōn- (whence the term Easter ). In Sioux mythology, Anpao is an entity with two faces.[ citation needed ]

The Hindu dawn deity Ushas is female, whereas Surya, the Sun, and Aruṇa, the Sun's charioteer, are male. Ushas is one of the most prominent Rigvedic deities. The time of dawn is also referred to as the Brahmamuhurtham (Brahma is the God of creation and muhurtham is a Hindu unit of time), and is considered an ideal time to perform spiritual activities, including meditation and yoga. In some parts of India, both Usha and Pratyusha (dusk) are worshiped along with the Sun during the festival of Chhath.[ citation needed ]

Jesus in the Bible is often symbolized by dawn in the morning, also when Jesus rose on the third day it happened during the morning. [7] Prime is the fixed time of prayer of the traditional Divine Office (Canonical Hours) in Christian liturgy, said at the first hour of daylight. Associated with Jesus, in Christianity, Christian burials take place in the direction of dawn.[ citation needed ]

In Judaism, the question of how to calculate dawn (Hebrew Alos/Alot HaShachar, or Alos/Alot) is posed by the Talmud, [8] as it has many ramifications for Jewish law (such as the possible start time for certain daytime commandments, like prayer). The simple reading of the Talmud is that dawn takes place 72 minutes before sunrise. Others, including the Vilna Gaon, have the understanding that the Talmud's timeframe for dawn was referring specifically to an equinox day in Mesopotamia, and is therefore teaching that dawn should be calculated daily as commencing when the Sun is 16.1 degrees below the horizon. The longstanding practice among most Sephardic Jews is to follow the first opinion, while many Ashkenazi Jews follow the latter view.[ citation needed ]

Dawn in art

Literature

An angel, robed in spotless white,
Bent down and kissed the sleeping Night.
Night woke to blush; the sprite was gone.
Men saw the blush and called it Dawn.
-Dawn by Paul Laurence Dunbar

See also

Related Research Articles

Generally, a day is roughly the time of one rotation of the Earth or one rotation of other large astronomical objects. In everyday life, the word "day" often refers to a solar day, which is the length between two solar noons or times the Sun reaches the highest point. The word "day" may also refer to daytime, a time period when the location receives direct and indirect sunlight. On Earth, as a location passes through its day, it experiences morning, noon, afternoon, evening, and night. The effect of a day is vital to many life processes, which is called the circadian rhythm.

A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and set "due west". This occurs twice each year, around 20 March and 23 September.

<span class="mw-page-title-main">Lunar phase</span> Shape of the Moons directly sunlit portion as viewed from Earth

Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the terminology of the 4 major phases: new moon, first quarter, full moon, last quarter and 4 minor phases: waxing crescent, waxing gibbous, waning gibbous, and waning crescent.

The heliacal rising or star rise of a star occurs annually, or the similar phenomenon of a planet, when it first becomes visible above the eastern horizon at dawn just before sunrise after a complete orbit of the earth around the sun. Historically, the most important such rising is that of Sirius, which was an important feature of the Egyptian calendar and astronomical development. The rising of the Pleiades heralded the start of the Ancient Greek sailing season, using celestial navigation.

<span class="mw-page-title-main">Sunrise</span> Time of day when the sun appears above the earth

Sunrise is the moment when the upper rim of the Sun appears on the horizon in the morning. The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects.

<span class="mw-page-title-main">Sunset</span> Daily falling of the Sun below the horizon

Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth, the equinox Sun sets due west at the moment of both the spring and autumn equinoxes. As viewed from the Northern Hemisphere, the Sun sets to the northwest in the spring and summer, and to the southwest in the autumn and winter; these seasons are reversed for the Southern Hemisphere.

<span class="mw-page-title-main">Dusk</span> Darkest stage of twilight, at end of astronomical twilight after sunset and just before night

Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before nightfall. At predusk, during early to intermediate stages of twilight, enough light in the sky under clear conditions may occur to read outdoors without artificial illumination; however, at the end of civil twilight, such lighting is required to read outside. The term dusk usually refers to astronomical dusk, or the darkest part of twilight before night begins.

<span class="mw-page-title-main">Night</span> Period of darkness during a 24-hour day

Night is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. The exact time when night begins and ends depends on the location and varies throughout the year, based on factors such as season and latitude.

<span class="mw-page-title-main">Midnight sun</span> Natural phenomenon when daylight lasts for a whole day

The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When the midnight sun is seen in the Arctic, the Sun appears to move from left to right, but in Antarctica the equivalent apparent motion is from right to left. This occurs at latitudes from 65°44' to 90° north or south, and does not stop exactly at the Arctic Circle or the Antarctic Circle, due to refraction.

<span class="mw-page-title-main">Twilight</span> Illumination of the atmosphere when the sun is not directly visible because it is below the horizon

Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. The word twilight can also refer to the periods of time when this illumination occurs.

<span class="mw-page-title-main">Polar night</span> Night lasting for more than 24 hours

The polar night is a phenomenon where the nighttime lasts for more than 24 hours that occurs in the northernmost and southernmost regions of Earth. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight sun, occurs when the Sun remains above the horizon for more than 24 hours.

<span class="mw-page-title-main">March equinox</span> When sun appears directly over equator

The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox in the Northern Hemisphere and as the autumnal equinox in the Southern Hemisphere.

<span class="mw-page-title-main">Blue hour</span> Period of twilight in the morning or evening

The blue hour is the period of twilight when the Sun is at a significant depth below the horizon. During this time, the remaining sunlight takes on a mostly blue shade. This shade differs from the colour of the sky on a clear day, which is caused by Rayleigh scattering.

<span class="mw-page-title-main">Sky brightness</span> Visual perception of the sky and how it scatters and diffuses light.

Sky brightness refers to the visual perception of the sky and how it scatters and diffuses light. The fact that the sky is not completely dark at night is easily visible. If light sources were removed from the night sky, only direct starlight would be visible.

<i>Zmanim</i> Hebrew terminology regarding appointed times

Zmanim are specific times of the day in Jewish law.

<span class="mw-page-title-main">Winter solstice</span> Astronomical phenomenon

The winter solstice, also called the hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere. For that hemisphere, the winter solstice is the day with the shortest period of daylight and longest night of the year, when the Sun is at its lowest daily maximum elevation in the sky. Either pole experiences continuous darkness or twilight around its winter solstice. The opposite event is the summer solstice.

<span class="mw-page-title-main">Daytime</span> Period of a day in which a location experiences natural illumination

Daytime as observed on Earth 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 a luminous primary body, such as a local star, also experience daytime, but this article primarily discusses daytime on Earth.

<span class="mw-page-title-main">Sun path</span> Arc-like path that the Sun appears to follow across the sky

Sun path, sometimes also called day arc, refers to the daily and seasonal arc-like path that the Sun appears to follow across the sky as the Earth rotates and orbits the Sun. The Sun's path affects the length of daytime experienced and amount of daylight received along a certain latitude during a given season.

<span class="mw-page-title-main">Season</span> Subdivision of the year based on orbit and axial tilt

A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historical cultures whose number of seasons varies.

Relative hour, sometimes called halachic hour, seasonal hour and variable hour, is a term used in rabbinic Jewish law that assigns 12 hours to each day and 12 hours to each night, all throughout the year. A relative hour has no fixed length in absolute time, but changes with the length of daylight each day - depending on summer, and in winter. Even so, in all seasons a day is always divided into 12 hours, and a night is always divided into 12 hours, which invariably makes for a longer hour or a shorter hour. At Mediterranean latitude, one hour can be about 45 minutes at the winter solstice, and 75 minutes at summer solstice. All of the hours mentioned by the Sages in either the Mishnah or Talmud, or in other rabbinic writings, refer strictly to relative hours.

References

  1. "The different types of twilight". timeanddate.com.
  2. Van Flandern, T.; K. Pulkkinen (1980). "Low precision formulae for planetary positions". Astrophysical Journal Supplement Series. 31 (3): 391. Bibcode:1979ApJS...41..391V. doi:10.1086/190623.
  3. "New Dawn at La Silla". ESO Picture of the Week. European Southern Observatory. Retrieved 27 February 2015.
  4. 1 2 3 National Oceanic and Atmospheric Administration. "Astronomical Terms".
  5. 1 2 3 "Dawn – Definition and Meaning".
  6. "مراد از صبح(فجر) صادق و کاذب چیست؟ - گنجینه پاسخ ها". اسلام کوئست - مرجعی برای پاسخگویی به سوالات دینی، اعتقادی و شرعی (in Persian). Retrieved 2022-11-04.
  7. "46 Bible verses about Dawn". bible.knowing-jesus.com. Retrieved 2021-11-06.
  8. Pesachim 94a
  9. Nihus, Barthold (1642). Epigrammata disticha. Johannes Kinckius.
  10. Williams, W. C., Dawn, poetry.com, accessed 10 September 2022