Apsis

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Apsis

The apsides refer to the farthest (2) and nearest (3) points reached by an orbiting planetary body (2 and 3) with respect to a primary, or host, body (1)

An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault'; pl. apsides /ˈæpsɪˌdiːz/ AP-sih-deez) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides is the line connecting the two extreme values.

Apsides pertaining to orbits around the Sun have distinct names to differentiate themselves from other apsides; these names are aphelion for the farthest and perihelion for the nearest point in the solar orbit. The Moon's two apsides are the farthest point, apogee, and the nearest point, perigee, of its orbit around the host Earth. Earth's two apsides are the farthest point, aphelion, and the nearest point, perihelion, of its orbit around the host Sun. The terms aphelion and perihelion apply in the same way to the orbits of Jupiter and the other planets, the comets, and the asteroids of the Solar System.

General description

The two-body system of interacting elliptic orbits: The smaller, satellite body (blue) orbits the primary body (yellow); both are in elliptic orbits around their common center of mass (or barycenter), (red +).
∗Periapsis and apoapsis as distances: the smallest and largest distances between the orbiter and its host body.

There are two apsides in any elliptic orbit. The name for each apsis is created from the prefixes ap-, apo- (from ἀπ(ό), (ap(o)-) 'away from') for the farthest or peri- (from περί (peri-) 'near') for the closest point to the primary body, with a suffix that describes the primary body. The suffix for Earth is -gee, so the apsides' names are apogee and perigee. For the Sun, the suffix is -helion, so the names are aphelion and perihelion.

According to Newton's laws of motion, all periodic orbits are ellipses. The barycenter of the two bodies may lie well within the bigger body—e.g., the Earth–Moon barycenter is about 75% of the way from Earth's center to its surface. If, compared to the larger mass, the smaller mass is negligible (e.g., for satellites), then the orbital parameters are independent of the smaller mass.

When used as a suffix—that is, -apsis—the term can refer to the two distances from the primary body to the orbiting body when the latter is located: 1) at the periapsis point, or 2) at the apoapsis point (compare both graphics, second figure). The line of apsides denotes the distance of the line that joins the nearest and farthest points across an orbit; it also refers simply to the extreme range of an object orbiting a host body (see top figure; see third figure).

In orbital mechanics, the apsides technically refer to the distance measured between the center of mass of the central body and the center of mass of the orbiting body. However, in the case of a spacecraft, the terms are commonly used to refer to the orbital altitude of the spacecraft above the surface of the central body (assuming a constant, standard reference radius).

Keplerian orbital elements: point G, the nearest point of approach of an orbiting body, is the pericenter (also periapsis) of an orbit; point H, the farthest point of the orbiting body, is the apocenter (also apoapsis) of the orbit; and the red line between them is the line of apsides.

Terminology

The words "pericenter" and "apocenter" are often seen, although periapsis/apoapsis are preferred in technical usage.

• For generic situations where the primary is not specified, the terms pericenter and apocenter are used for naming the extreme points of orbits (see table, top figure); periapsis and apoapsis (or apapsis) are equivalent alternatives, but these terms also frequently refer to distances—that is, the smallest and largest distances between the orbiter and its host body (see second figure).
• For a body orbiting the Sun, the point of least distance is the perihelion (/ˌpɛrɪˈhiːliən/), and the point of greatest distance is the aphelion (/æpˈhiːliən/); when discussing orbits around other stars the terms become periastron and apastron.
• When discussing a satellite of Earth, including the Moon, the point of least distance is the perigee (/ˈpɛrɪdʒiː/), and of greatest distance, the apogee (from Ancient Greek: Γῆ (Gē), "land" or "earth").
• For objects in lunar orbit, the point of least distance are called the pericynthion (/ˌpɛrɪˈsɪnθiən/) and the greatest distance the apocynthion (/ˌæpəˈsɪnθiən/). The terms perilune and apolune, as well as periselene and aposelene are also used. Since the Moon has no natural satellites this only applies to man-made objects.

Etymology

The words perihelion and aphelion were coined by Johannes Kepler to describe the orbital motions of the planets around the Sun. The words are formed from the prefixes peri- (Greek: περί, near) and apo- (Greek: ἀπό, away from), affixed to the Greek word for the Sun, (ἥλιος, or hēlíos).

Various related terms are used for other celestial objects. The suffixes -gee, -helion, -astron and -galacticon are frequently used in the astronomical literature when referring to the Earth, Sun, stars, and the Galactic Center respectively. The suffix -jove is occasionally used for Jupiter, but -saturnium has very rarely been used in the last 50 years for Saturn. The -gee form is also used as a generic closest-approach-to "any planet" term—instead of applying it only to Earth.

During the Apollo program, the terms pericynthion and apocynthion were used when referring to orbiting the Moon; they reference Cynthia, an alternative name for the Greek Moon goddess Artemis. More recently, during the Artemis program, the terms perilune and apolune have been used.

Regarding black holes, the term peribothron was first used in a 1976 paper by J. Frank and M. J. Rees, who credit W. R. Stoeger for suggesting creating a term using the greek word for pit: "bothron".

The terms perimelasma and apomelasma (from a Greek root) were used by physicist and science-fiction author Geoffrey A. Landis in a story published in 1998, thus appearing before perinigricon and aponigricon (from Latin) in the scientific literature in 2002.

Terminology summary

The suffixes shown below may be added to prefixes peri- or apo- to form unique names of apsides for the orbiting bodies of the indicated host/(primary) system. However, only for the Earth, Moon and Sun systems are the unique suffixes commonly used. Exoplanet studies commonly use -astron, but typically, for other host systems the generic suffix, -apsis, is used instead.

Host objects in the Solar System with named/nameable apsides

Astronomical host object	Suffix	Origin of the name
Sun	-helion	Helios
Mercury	-hermion	Hermes
Venus	-cythe	Cytherean
Earth	-gee	Gaia
Moon	-lune -cynthion -selene	Luna Cynthia Selene
Mars	-areion	Ares
Ceres	-demeter	Demeter
Jupiter	-jove	Zeus Jupiter
Saturn	-chron -kronos -saturnium -krone	Cronos Saturn
Uranus	-uranion	Uranus
Neptune	-poseideum -poseidion	Poseidon

Other host objects with named/nameable apsides

Astronomical host object	Suffix	Origin of the name
Star	-astron	Lat: astra; stars
Galaxy	-galacticon	Gr: galaxias; galaxy
Barycenter	-center -focus -apsis
Black hole	-melasma -bothron -nigricon	Gr: melos; black Gr: bothros; hole Lat: niger; black

Perihelion and aphelion

"Perihelion" redirects here. For other uses, see Perihelion (disambiguation).

"Aphelion" redirects here. For other uses, see Aphelion (disambiguation).

Diagram of a body's direct orbit around the Sun with its nearest (perihelion) and farthest (aphelion) points

The perihelion (q) and aphelion (Q) are the nearest and farthest points respectively of a body's direct orbit around the Sun.

Comparing osculating elements at a specific epoch to effectively those at a different epoch will generate differences. The time-of-perihelion-passage as one of six osculating elements is not an exact prediction (other than for a generic two-body model) of the actual minimum distance to the Sun using the full dynamical model. Precise predictions of perihelion passage require numerical integration.

Inner planets and outer planets

The two images below show the orbits, orbital nodes, and positions of perihelion (q) and aphelion (Q) for the planets of the Solar System as seen from above the northern pole of Earth's ecliptic plane, which is coplanar with Earth's orbital plane. The planets travel counterclockwise around the Sun and for each planet, the blue part of their orbit travels north of the ecliptic plane, the pink part travels south, and dots mark perihelion (green) and aphelion (orange).

The first image (below-left) features the inner planets, situated outward from the Sun as Mercury, Venus, Earth, and Mars. The reference Earth-orbit is colored yellow and represents the orbital plane of reference. At the time of vernal equinox, the Earth is at the bottom of the figure. The second image (below-right) shows the outer planets, being Jupiter, Saturn, Uranus, and Neptune.

The orbital nodes are the two end points of the "line of nodes" where a planet's tilted orbit intersects the plane of reference; here they may be 'seen' as the points where the blue section of an orbit meets the pink.

• 
  The perihelion (green) and aphelion (orange) points of the inner planets of the Solar System
• 
  The perihelion (green) and aphelion (orange) points of the outer planets of the Solar System

Lines of apsides

The chart shows the extreme range—from the closest approach (perihelion) to farthest point (aphelion)—of several orbiting celestial bodies of the Solar System: the planets, the known dwarf planets, including Ceres, and Halley's Comet. The length of the horizontal bars correspond to the extreme range of the orbit of the indicated body around the Sun. These extreme distances (between perihelion and aphelion) are the lines of apsides of the orbits of various objects around a host body.

Distances of selected bodies of the Solar System from the Sun. The left and right edges of each bar correspond to the perihelion and aphelion of the body, respectively, hence long bars denote high orbital eccentricity. The radius of the Sun is 0.7 million km, and the radius of Jupiter (the largest planet) is 0.07 million km, both too small to resolve on this image.

Earth perihelion and aphelion

Currently, the Earth reaches perihelion in early January, approximately 14 days after the December solstice. At perihelion, the Earth's center is about 0.98329 astronomical units (AU) or 147,098,070 km (91,402,500 mi) from the Sun's center. In contrast, the Earth reaches aphelion currently in early July, approximately 14 days after the June solstice. The aphelion distance between the Earth's and Sun's centers is currently about 1.01671 AU or 152,097,700 km (94,509,100 mi).

The dates of perihelion and aphelion change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. In the short term, such dates can vary up to 2 days from one year to another. This significant variation is due to the presence of the Moon: while the Earth–Moon barycenter is moving on a stable orbit around the Sun, the position of the Earth's center which is on average about 4,700 kilometres (2,900 mi) from the barycenter, could be shifted in any direction from it—and this affects the timing of the actual closest approach between the Sun's and the Earth's centers (which in turn defines the timing of perihelion in a given year).

Because of the increased distance at aphelion, only 93.55% of the radiation from the Sun falls on a given area of Earth's surface as does at perihelion, but this does not account for the seasons, which result instead from the tilt of Earth's axis of 23.4° away from perpendicular to the plane of Earth's orbit. Indeed, at both perihelion and aphelion it is summer in one hemisphere while it is winter in the other one. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, regardless of the Earth's distance from the Sun.

In the northern hemisphere, summer occurs at the same time as aphelion, when solar radiation is lowest. Despite this, summers in the northern hemisphere are on average 2.3 °C (4 °F) warmer than in the southern hemisphere, because the northern hemisphere contains larger land masses, which are easier to heat than the seas.

Perihelion and aphelion do however have an indirect effect on the seasons: because Earth's orbital speed is minimum at aphelion and maximum at perihelion, the planet takes longer to orbit from June solstice to September equinox than it does from December solstice to March equinox. Therefore, summer in the northern hemisphere lasts slightly longer (93 days) than summer in the southern hemisphere (89 days).

Astronomers commonly express the timing of perihelion relative to the First Point of Aries not in terms of days and hours, but rather as an angle of orbital displacement, the so-called longitude of the periapsis (also called longitude of the pericenter). For the orbit of the Earth, this is called the longitude of perihelion, and in 2000 it was about 282.895°; by 2010, this had advanced by a small fraction of a degree to about 283.067°, i.e. a mean increase of 62" per year.

For the orbit of the Earth around the Sun, the time of apsis is often expressed in terms of a time relative to seasons, since this determines the contribution of the elliptical orbit to seasonal variations. The variation of the seasons is primarily controlled by the annual cycle of the elevation angle of the Sun, which is a result of the tilt of the axis of the Earth measured from the plane of the ecliptic. The Earth's eccentricity and other orbital elements are not constant, but vary slowly due to the perturbing effects of the planets and other objects in the solar system (Milankovitch cycles).

On a very long time scale, the dates of the perihelion and of the aphelion progress through the seasons, and they make one complete cycle in 22,000 to 26,000 years. There is a corresponding movement of the position of the stars as seen from Earth, called the apsidal precession. (This is closely related to the precession of the axes.) The dates and times of the perihelions and aphelions for several past and future years are listed in the following table:

Year	Perihelion		Aphelion
	Date	Time (UT)	Date	Time (UT)
2010	January 3	00:09	July 6	11:30
2011	January 3	18:32	July 4	14:54
2012	January 5	00:32	July 5	03:32
2013	January 2	04:38	July 5	14:44
2014	January 4	11:59	July 4	00:13
2015	January 4	06:36	July 6	19:40
2016	January 2	22:49	July 4	16:24
2017	January 4	14:18	July 3	20:11
2018	January 3	05:35	July 6	16:47
2019	January 3	05:20	July 4	22:11
2020	January 5	07:48	July 4	11:35
2021	January 2	13:51	July 5	22:27
2022	January 4	06:55	July 4	07:11
2023	January 4	16:17	July 6	20:07
2024	January 3	00:39	July 5	05:06
2025	January 4	13:28	July 3	19:55
2026	January 3	17:16	July 6	17:31
2027	January 3	02:33	July 5	05:06
2028	January 5	12:28	July 3	22:18
2029	January 2	18:13	July 6	05:12

Other planets

The following table shows the distances of the planets and dwarf planets from the Sun at their perihelion and aphelion.

Type of body	Body	Distance from Sun at perihelion	Distance from Sun at aphelion	difference (%)	insolation difference (%)
Planet	Mercury	46,001,009 km (28,583,702 mi)	69,817,445 km (43,382,549 mi)	34%	57%
	Venus	107,476,170 km (66,782,600 mi)	108,942,780 km (67,693,910 mi)	1.3%	2.8%
	Earth	147,098,291 km (91,402,640 mi)	152,098,233 km (94,509,460 mi)	3.3%	6.5%
	Mars	206,655,215 km (128,409,597 mi)	249,232,432 km (154,865,853 mi)	17%	31%
	Jupiter	740,679,835 km (460,237,112 mi)	816,001,807 km (507,040,016 mi)	9.2%	18%
	Saturn	1,349,823,615 km (838,741,509 mi)	1,503,509,229 km (934,237,322 mi)	10%	19%
	Uranus	2,734,998,229 km (1.699449110×109 mi)	3,006,318,143 km (1.868039489×109 mi)	9.0%	17%
	Neptune	4,459,753,056 km (2.771162073×109 mi)	4,537,039,826 km (2.819185846×109 mi)	1.7%	3.4%
Dwarf planet	Ceres	380,951,528 km (236,712,305 mi)	446,428,973 km (277,398,103 mi)	15%	27%
	Pluto	4,436,756,954 km (2.756872958×109 mi)	7,376,124,302 km (4.583311152×109 mi)	40%	64%
	Haumea	5,157,623,774 km (3.204798834×109 mi)	7,706,399,149 km (4.788534427×109 mi)	33%	55%
	Makemake	5,671,928,586 km (3.524373028×109 mi)	7,894,762,625 km (4.905578065×109 mi)	28%	48%
	Eris	5,765,732,799 km (3.582660263×109 mi)	14,594,512,904 km (9.068609883×109 mi)	60%	84%

Mathematical formulae

These formulae characterize the pericenter and apocenter of an orbit:

Pericenter

Maximum speed, $v_{\text{per}}=\sqrt{\frac{(1+e)\mu }{(1-e)a}}$, at minimum (pericenter) distance, $r_{\text{per}}=(1-e)a$.

Apocenter

Minimum speed, $v_{\text{ap}}=\sqrt{\frac{(1-e)\mu }{(1+e)a}}$, at maximum (apocenter) distance, $r_{\text{ap}}=(1+e)a$.

While, in accordance with Kepler's laws of planetary motion (based on the conservation of angular momentum) and the conservation of energy, these two quantities are constant for a given orbit:

Specific relative angular momentum

${\displaystyle h=\sqrt{\left(1-e^2\right)\mu a}}$

Specific orbital energy

${\displaystyle \epsilon =-\frac{\mu }{2a}}$

where:

• $r_{\text{ap}}$ is the distance from the apocenter to the primary focus
• $r_{\text{per}}$ is the distance from the pericenter to the primary focus
• a is the semi-major axis:

  ${\displaystyle a=\frac{r_{\text{per}}+r_{\text{ap}}}{2}}$

• μ is the standard gravitational parameter
• e is the eccentricity, defined as

  ${\displaystyle e=\frac{r_{\text{ap}}-r_{\text{per}}}{r_{\text{ap}}+r_{\text{per}}}=1-\frac{2}{\frac{r_{\text{ap}}}{r_{\text{per}}}+1}}$

Note that for conversion from heights above the surface to distances between an orbit and its primary, the radius of the central body has to be added, and conversely.

The arithmetic mean of the two limiting distances is the length of the semi-major axis a. The geometric mean of the two distances is the length of the semi-minor axis b.

The geometric mean of the two limiting speeds is

${\displaystyle \sqrt{-2\epsilon }=\sqrt{\frac{\mu }{a}}}$

which is the speed of a body in a circular orbit whose radius is ${\displaystyle a}$.

Time of perihelion

Orbital elements such as the time of perihelion passage are defined at the epoch chosen using an unperturbed two-body solution that does not account for the n-body problem. To get an accurate time of perihelion passage you need to use an epoch close to the perihelion passage. For example, using an epoch of 1996, Comet Hale–Bopp shows perihelion on 1 April 1997. Using an epoch of 2008 shows a less accurate perihelion date of 30 March 1997. Short-period comets can be even more sensitive to the epoch selected. Using an epoch of 2005 shows 101P/Chernykh coming to perihelion on 25 December 2005, but using an epoch of 2012 produces a less accurate unperturbed perihelion date of 20 January 2006.

Numerical integration shows dwarf planet Eris will come to perihelion around December 2257. Using an epoch of 2021, which is 236 years early, less accurately shows Eris coming to perihelion in 2260.

4 Vesta came to perihelion on 26 December 2021, but using a two-body solution at an epoch of July 2021 less accurately shows Vesta came to perihelion on 25 December 2021.

Short arcs

Trans-Neptunian objects discovered when 80+ AU from the Sun need dozens of observations over multiple years to well constrain their orbits because they move very slowly against the background stars. Due to statistics of small numbers, trans-Neptunian objects such as 2015 TH367 when it had only 8 observations over an observation arc of 1 year that have not or will not come to perihelion for roughly 100 years can have a 1-sigma uncertainty of 77.3 years (28,220 days) in the perihelion date.

Flood myth

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Flood_myth

"The Deluge", frontispiece to Gustave Doré's illustrated edition of the Bible

A flood myth or a deluge myth is a myth in which a great flood, usually sent by a deity or deities, destroys civilization, often in an act of divine retribution. Parallels are often drawn between the flood waters of these myths and the primeval waters which appear in certain creation myths, as the flood waters are described as a measure for the cleansing of humanity, in preparation for rebirth. Most flood myths also contain a culture hero, who "represents the human craving for life".

The flood-myth motif occurs in many cultures, including the manvantara-sandhya in Hinduism, Deucalion and Pyrrha in Greek mythology, the Genesis flood narrative, the Mesopotamian flood stories, and the Cheyenne flood story.

Mythologies

One example of a flood myth is in the Epic of Gilgamesh. Many scholars believe that this account was copied from the Akkadian Atra-Hasis, which dates to the 18th century BCE. In the Gilgamesh flood myth, the highest god, Enlil, decides to destroy the world with a flood because humans have become too noisy. The god Ea, who had created humans out of clay and divine blood, secretly warns the hero Utnapishtim of the impending flood and gives him detailed instructions for building a boat so that life may survive. Both the Epic of Gilgamesh and Atra-Hasis are preceded by the similar Eridu Genesis (c. 1600 BCE)—the oldest surviving example of such a flood-myth narrative, known from tablets found in the ruins of Nippur in the late 1890s and translated by assyriologist Arno Poebel.

George Smith, who discovered and translated the Epic of Gilgamesh

Academic Yi Samuel Chen analyzed various texts from the Early Dynastic III Period through to the Old Babylonian Period, and argues that the flood narrative was only added in texts written during the Old Babylonian Period. With regard to the Sumerian King List, observations by experts have always indicated that the portion of the Sumerian King List talking about before the flood differs stylistically from the King List Proper. Essentially Old Babylonian copies tend to represent a tradition of before the flood apart from the actual King List, whereas the Ur III copy of the King List and the duplicate from the Brockmon collection indicate that the King List Proper once existed independent of mention of the flood and the tradition of before the flood. Essentially, Chen gives evidence to prove that the section of before the flood and references to the flood in the Sumerian King List were all later additions added in during the Old Babylonian Period, as the Sumerian King List went through updates and edits. The flood as a watershed in early history of the world was probably a new historiographical concept emerging in the Mesopotamian literary traditions during the Old Babylonian Period, as evident by the fact that the flood motif did not show up in the Ur III copy and that earliest chronographical sources related to the flood show up in the Old Babylonian Period. Chen also concludes that the name of "Ziusudra" as a flood hero and the idea of the flood hinted at by that name in the Old Babylonian Version of "Instructions of Shuruppak" are only developments during that Old Babylonian Period, when also the didactic text was updated with information from the burgeoning Antediluvian Tradition.

In the Hebrew Genesis, the god Yahweh, who had created man out of the dust of the ground, decides to flood the earth because of the corrupted state of mankind. Yahweh then gives the protagonist, Noah, instructions to build an ark in order to preserve human and animal life. When the ark is completed, Noah, his family, and representatives of all the animals of the earth are called upon to enter the ark. When the destructive flood begins, all life outside of the ark perishes. After the waters recede, all those aboard the ark disembark and have Yahweh's promise that he will never judge the earth with a flood again. Yahweh causes a rainbow to form as the sign of this promise.

In Hindu mythology, texts such as the Satapatha Brahmana (c. 6th century BCE) and the Puranas contain the story of a great flood, "manvantara-sandhya", wherein the Matsya Avatar of the Vishnu warns the first man, Manu, of the impending flood, and also advises him to build a giant boat. In Zoroastrian Mazdaism, Ahriman tries to destroy the world with a drought, which Mithra ends by shooting an arrow into a rock, from which a flood springs; one man survives in an ark with his cattle. Norbert Oettinger argues that the story of Yima and the Vara was originally a flood myth, and the harsh winter was added in due to the dry nature of Eastern Iran, as flood myths did not have as much of an effect as harsh winters. He has argued that the mention of melted water flowing in Videvdad 2.24 is a remnant of the flood myth, and mentions that the Indian flood myths originally had their protagonist as Yama, but it was changed to Manu later.

In Plato's Timaeus, written c. 360 BCE, Timaeus describes a flood myth similar to the earlier versions. In it, the Bronze race of humans angers the high god Zeus with their constant warring. Zeus decides to punish humanity with a flood. The Titan Prometheus, who had created humans from clay, tells the secret plan to Deucalion, advising him to build an ark in order to be saved. After nine nights and days, the water starts receding and the ark lands on a mountain.

The Cheyenne, a North American Great Plains tribe, believe in a flood which altered the course of their history, perhaps occurring in the Missouri River Valley.

Historicity

Floods in the wake of the Last Glacial Period (c. 115,000 – c. 11,700 years ago) are speculated to have inspired myths that survive to this day. Plato's allegory of Atlantis is set over 9,000 years before his time, leading some scholars to suggest that a Stone Age society which lived close to the Mediterranean Sea could have been wiped out by the rising sea level, an event which could have served as the basis for the story.

Archaeologist Bruce Masse stated that some of the narratives of a great flood discovered in many cultures around the world may be linked to an oceanic asteroid impact that occurred between Africa and Antarctica, around the time of a solar eclipse, that caused a tsunami. Among the 175 myths he analyzed were a Hindu myth speaking of an alignment of the five planets at the time, and a Chinese story linking the flood to the end of the reign of Empress Nu Wa. Fourteen flood myths refer to a full solar eclipse. According to Masse these indications point to the date May 10, 2807 BC. His hypothesis suggests that a meteor or comet crashed into the Indian Ocean around 3000–2800 BCE, and created the 18-mile (29 km) undersea Burckle Crater and Fenambosy Chevron, and generated a giant tsunami that flooded coastal lands.^[29]

Mesopotamia

Mesopotamia, like other early sites of riverine civilisation, was flood-prone; and for those experiencing valley-wide inundations, flooding could destroy the whole of their known world. According to the excavation report of the 1930s excavation at Shuruppak (modern Tell Fara, Iraq), the Jemdet Nasr and Early Dynastic layers at the site were separated by a 60-cm yellow layer of alluvial sand and clay, indicating a flood, like that created by river avulsion, a process common in the Tigris–Euphrates river system. Similar layers have been recorded at other sites as well, all dating to different periods, which would be consistent with the nature of river avulsions. Shuruppak in Mesopotamian legend was the city of Uta-napishtim, the king who built a boat to survive the coming flood. The alluvial layer dates from around 2900 BC.

Earth's sea level rose dramatically in the millennia after the Last Glacial Maximum.

The geography of the Mesopotamian area changed considerably with the filling of the Persian Gulf after sea waters rose following the last glacial period. Global sea levels were about 120 m (390 ft) lower around 18,000 BP and rose until 8,000 BP when they reached current levels, which are now an average 40 m (130 ft) above the floor of the Gulf, which was a huge (800 km × 200 km, 500 mi × 120 mi) low-lying and fertile region in Mesopotamia, in which human habitation is thought to have been strong around the Gulf Oasis for 100,000 years. A sudden increase in settlements above the present-day water level is recorded at around 7,500 BP.

Mediterranean Basin

The historian Adrienne Mayor theorizes that global flood stories may have been inspired by ancient observations of seashells and fish fossils in inland and mountain areas. The ancient Greeks, Egyptians, and Romans all documented the discovery of such remains in such locations; the Greeks hypothesized that Earth had been covered by water on several occasions, citing the seashells and fish fossils found on mountain tops as evidence of this idea.

Speculation regarding the Deucalion myth has postulated a large tsunami in the Mediterranean Sea, caused by the Thera eruption (with an approximate geological date of 1630–1600 BCE), as the myth's historical basis. Although the tsunami hit the South Aegean Sea and Crete, it did not affect cities in the mainland of Greece, such as Mycenae, Athens, and Thebes, which continued to prosper, indicating that it had a local rather than a region-wide effect.

Black Sea deluge hypothesis

The Black Sea deluge hypothesis offers a controversial account of long-term flooding; the hypothesis argues for a catastrophic irruption of water about 5600 BCE from the Mediterranean Sea into the Black Sea basin. This has become the subject of considerable discussion.^[38][39] The Younger Dryas impact hypothesis offered another proposed natural explanation for flood myths. However, this idea was similarly controversial and has been refuted.

Comets

The Eve of the Deluge, by John Martin, 1840. Depicts a comet causing the Great Flood.

The earliest known hypothesis about a comet that had a widespread effect on human populations can be attributed to Edmond Halley, who in 1694 suggested that a worldwide flood had been the result of a near-miss by a comet. The issue was taken up in more detail by William Whiston, a protégé of and popularizer of the theories of Isaac Newton, who argued in his book A New Theory of the Earth (1696) that a comet encounter was the probable cause of the Biblical Flood of Noah in 2342 BCE. Whiston also attributed the origins of the atmosphere and other significant changes in the Earth to the effects of comets.

In Pierre-Simon Laplace's book Exposition Du Systême Du Monde (The System of the World), first published in 1796, he stated:

[T]he greater part of men and animals drowned in a universal deluge, or destroyed by the violence of the shock given to the terrestrial globe; whole species destroyed; all the monuments of human industry reversed: such are the disasters which a shock of a comet would produce.

A similar hypothesis was popularized by Minnesota congressman and pseudoarchaeology writer Ignatius L. Donnelly in his book Ragnarok: The Age of Fire and Gravel (1883), which followed his better-known book Atlantis: The Antediluvian World (1882). In Ragnarok, Donnelly argued that an enormous comet struck the Earth around 6,000 BCE to 9,000 BCE, destroying an advanced civilization on the "lost continent" of Atlantis. Donnelly, following others before him, attributed the Biblical Flood to this event, which he hypothesized had also resulted in catastrophic fires and climate change. Shortly after the publication of Ragnarok, one commenter noted, "Whiston ascertained that the deluge of Noah came from a comet's tail; but Donnelly has outdone Whiston, for he has shown that our planet has suffered not only from a cometary flood, but from cometary fire, and a cometary rain of stones."

Russian web brigades

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Russian_web_brigades

Russian web brigades, also called Russian trolls, Russian bots, Kremlinbots, or Kremlin trolls are state-sponsored anonymous Internet political commentators and trolls linked to the Government of Russia. Participants report that they are organized into teams and groups of commentators that participate in Russian and international political blogs and Internet forums using sockpuppets, social bots, and large-scale orchestrated trolling and disinformation campaigns to promote pro-Vladimir Putin and pro-Russian propaganda.

Kremlin trolls are closely tied to the Internet Research Agency, a Saint Petersburg-based company run by Yevgeny Prigozhin, who was a close ally to Putin and head of the mercenary Wagner Group, known for committing war crimes before his death in 2023. Articles on the Russian Wikipedia concerning the MH17 crash and the Russo-Ukrainian War were targeted by Russian internet propaganda outlets. In June 2019, a group of 12 editors introducing coordinated pro-government and anti-opposition bias was blocked on the Russian-language Wikipedia. During the Russian invasion of Ukraine in 2022, Kremlin trolls were still active on many social platforms and were spreading disinformation related to the war events.

Background

Main articles: Russian disinformation, Propaganda in Russia, and Media freedom in Russia

The earliest documented allegations of the existence of "web brigades" appear to be in the April 2003 Vestnik Online article "The Virtual Eye of Big Brother" by French journalist Anna Polyanskaya (a former assistant to assassinated Russian politician Galina Starovoitova) and two other authors, Andrey Krivov and Ivan Lomako. The authors claim that up to 1998, contributions to forums on Russian Internet sites (Runet) predominantly reflected liberal and democratic values, but after 2000, the vast majority of contributions reflected totalitarian values. This sudden change was attributed to the appearance of teams of pro-Russian commenters who appeared to be organized by the Russian state security service. According to the authors, about 70% of Russian Internet posters were of generally liberal views prior to 1998–1999, while a surge of "antidemocratic" posts (about 60–80%) suddenly occurred at many Russian forums in 2000. This could also be a reflection to the fact that access to Internet among the general Russian population soared during this time, which was until then accessible only to some sections of the society.

In January 2012, a hacktivist group calling itself the Russian arm of Anonymous published a massive collection of email allegedly belonging to former and present leaders of the pro-Putin youth organization Nashi (including a number of government officials). Journalists who investigated the leaked information found that the pro-Putin movement had engaged in a range of activities including paying commentators to post content and hijacking blog ratings in the fall of 2011. The e-mails indicated that members of the "brigades" were paid 85 rubles (about US$3) or more per comment, depending on whether the comment received replies. Some were paid as much as 600,000 roubles (about US$21,000) for leaving hundreds of comments on negative press articles on the internet, and were presented with iPads. A number of high-profile bloggers were also mentioned as being paid for promoting Nashi and government activities. The Federal Youth Agency, whose head (and the former leader of Nashi) Vasily Yakemenko was the highest-ranking individual targeted by the leaks, refused to comment on the authenticity of the e-mails.

In 2013, a Freedom House report stated that 22 of 60 countries examined have been using paid pro-government commentators to manipulate online discussions, and that Russia has been at the forefront of this practice for several years, along with China and Bahrain. In the same year, Russian reporters investigated the St. Petersburg Internet Research Agency, which employs at least 400 people. They found that the agency covertly hired young people as "Internet operators" paid to write pro-Russian postings and comments, smearing opposition leader Alexei Navalny and U.S. politics and culture.

Each commenter was to write no less than 100 comments a day, while people in the other room were to write four postings a day, which then went to the other employees whose job was to post them on social networks as widely as possible.

Some Russian opposition journalists state that such practices create a chilling effect on the few independent media outlets remaining in the country.

Further investigations were performed by Russian opposition newspaper Novaya Gazeta and Institute of Modern Russia in 2014–15, inspired by the peak of activity of the pro-Russian brigades during the Russo-Ukrainian War and assassination of Boris Nemtsov. The effort of using "troll armies" to promote Putin's policies is reported to be a multimillion-dollar operation. According to an investigation by the British Guardian newspaper, the flood of pro-Russian comments is part of a coordinated "informational-psychological war operation". One Twitter bot network was documented to use more than 20,500 fake Twitter accounts to spam negative comments after the death of Boris Nemtsov and events related to the Ukrainian conflict.

An article based on the original Polyanskaya article, authored by the Independent Customers' Association, was published in May 2008 at Expertiza.Ru. In this article the term web brigades is replaced by the term Team "G".

During his presidency, Donald Trump retweeted a tweet by a fake account operated by Russians. In 2017, he was among almost 40 celebrities and politicians, along with over 3,000 global news outlets, identified to have inadvertently shared content from Russian troll-farm accounts.

Methods

Web brigades commentators sometimes leave hundreds of postings a day that criticize the country's opposition and promote Kremlin-backed policymakers. Commentators simultaneously react to discussions of "taboo" topics, including the historical role of Soviet leader Joseph Stalin, political opposition, dissidents such as Mikhail Khodorkovsky, murdered journalists, and cases of international conflict or rivalry (with countries such as Estonia, Georgia, and Ukraine, but also with the foreign policies of the United States and the European Union). Prominent journalist and Russia expert Peter Pomerantsev believes Russia's efforts are aimed at confusing the audience, rather than convincing it. He states that they cannot censor information but can "trash it with conspiracy theories and rumours".

To avert suspicions, the users sandwich political remarks between neutral articles on travelling, cooking and pets. They overwhelm comment sections of media to render meaningful dialogue impossible.

The effect created by such Internet trolls is not very big, but they manage to make certain forums meaningless because people stop commenting on the articles when these trolls sit there and constantly create an aggressive, hostile atmosphere toward those whom they don’t like. The trolls react to certain news with torrents of mud and abuse. This makes it meaningless for a reasonable person to comment on anything there.

A collection of leaked documents, published by Moy Rayon, suggests that work at the "troll den" is strictly regulated by a set of guidelines. Any blog post written by an agency employee, according to the leaked files, must contain "no fewer than 700 characters" during day shifts and "no fewer than 1,000 characters" on night shifts. Use of graphics and keywords in the post's body and headline is also mandatory. In addition to general guidelines, bloggers are also provided with "technical tasks" – keywords and talking points on specific issues, such as Ukraine, Russia's internal opposition and relations with the West. On an average working day, the workers are to post on news articles 50 times. Each blogger is to maintain six Facebook accounts publishing at least three posts a day and discussing the news in groups at least twice a day. By the end of the first month, they are expected to have won 500 subscribers and get at least five posts on each item a day. On Twitter, the bloggers are expected to manage 10 accounts with up to 2,000 followers and tweet 50 times a day.

Timeline

Main article: Internet Research Agency

In 2015, Lawrence Alexander disclosed a network of propaganda websites sharing the same Google Analytics identifier and domain registration details, allegedly run by Nikita Podgorny from Internet Research Agency. The websites were mostly meme repositories focused on attacking Ukraine, Euromaidan, Russian opposition and Western policies. Other websites from this cluster promoted president Putin and Russian nationalism, and spread alleged news from Syria presenting anti-Western and pro-Bashar al-Assad viewpoints.

In August 2015, Russian researchers correlated Google search statistics of specific phrases with their geographic origin, observing increases in specific politically loaded phrases (such as "Poroshenko", "Maidan", "sanctions") starting from 2013 and originating from very small, peripheral locations in Russia, such as Olgino, which also happens to be the headquarters of the Internet Research Agency company. The Internet Research Agency also appears to be the primary sponsor of an anti-Western exhibition Material Evidence.

Since 2015, Finnish reporter Jessikka Aro has inquired into web brigades and Russian trolls. In addition, Western journalists have referred to the phenomenon and have supported traditional media.

In May 2019, it was reported that a study from the George Washington University found that Russian Twitter bots had tried to inflame the United States' anti-vaccination debate by posting opinions on both sides in 2018.

In June 2019 a group of 12 editors introducing coordinated pro-government and anti-opposition bias was blocked on the Russian-language Wikipedia. In July 2019 two operatives of the Internet Research Agency were detained in Libya and charged with attempting to influence local elections. They were reportedly employees of Alexander Malkevich, manager of USA Really, a propaganda website.

In 2020, the research firm Graphika published a report detailing one particular Russian disinformation group codenamed "Secondary Infektion" (alluding to 80's Operation Infektion) operating running since 2014. Over 6 years the group published over 2,500 items in seven languages and to over 300 platforms such as social media (Facebook, Twitter, YouTube, Reddit) and discussion forums. The group specialized in highly divisive topics regarding immigration, environment, politics, international relations and frequently used fake images presented as "leaked documents".

Starting in February 2022, a special attempt was made to back the Russian war in Ukraine. Particular effort was made to target Facebook and YouTube.

Russian invasion of Ukraine

Further information: Disinformation in the Russian invasion of Ukraine and Russian information war against Ukraine

In May 2022, during the Russian invasion of Ukraine, the trolls allegedly hired by Internet Research Agency (IRA) had reportedly extended their foothold into TikTok, spreading misinformation on war events and attempting to question or sow doubt about the Ukraine war. Authentic-looking profiles had allegedly hundreds of thousands of followers. IRA was reported to be active across different platforms, including Instagram and Telegram.

Egyptian pyramid construction techniques

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Egyptian_pyramid_construction_techniques 

The three main pyramids at Giza, together with subsidiary pyramids and the remains of other ancient structures

Egyptian pyramid construction techniques are the controversial subject of many hypotheses. These techniques seem to have developed over time; later pyramids were not constructed in the same way as earlier ones. Most of the construction hypotheses are based on the belief that huge stones were carved from quarries with copper chisels, and these blocks were then dragged and lifted into position. Disagreements chiefly concern the methods used to move and place the stones.

In addition to the many unresolved arguments about the construction techniques, there have been disagreements as to the kind of workforce used. The Greeks, many years after the event, believed that the pyramids were built by slave labour. Archaeologists now believe that the Great Pyramid of Giza (at least) was built by tens of thousands of skilled workers who camped near the pyramids and worked for a salary or as a form of tax payment (levy) until the construction was completed, pointing to workers' cemeteries discovered in 1990. For the Middle Kingdom pyramid of Amenemhat II, there is evidence from the annal stone of the king that foreigners from Canaan were employed.

A number of pseudoscientific theories have been put forth to explain how the pyramids were built.

Historical hypotheses

Writings of Herodotus and Diodorus Siculus

The unknowns of pyramid construction chiefly center on the question of how the blocks were moved up the superstructure. There is no known accurate historical or archaeological evidence that definitively resolves the question. Therefore, most discussion on construction methods involves functional possibilities that are supported by limited historical and archaeological evidence.

The first historical accounts of the construction of these monuments came centuries after the era of pyramid construction, by Herodotus in the 5th century BC and Diodorus Siculus in the 1st century BC. Herodotus's account claims that the Egyptians used a machine (now commonly referred to as the "Herodotus Machine"), stating:

A machine lifting a large stone column, by Leonardo da Vinci. Believed to be sketched based on Herodotus' description

This pyramid was made like stairs, which some call steps and others, tiers. When this, its first form, was completed, the workmen used short wooden logs as levers to raise the rest of the stones; they heaved up the blocks from the ground onto the first tier of steps; when the stone had been raised, it was set on another lever that stood on the first tier, and the lever again used to lift it from this tier to the next. It may be that there was a new lever on each tier of steps, or perhaps there was only one lever, quite portable, which they carried up to each tier in turn; I leave this uncertain, as both possibilities were mentioned. But this is certain, that the upper part of the pyramid was finished off first, then the next below it, and last of all the base and the lowest part.

Diodorus Siculus's account states:

And it's said the stone was transported a great distance from Arabia, and that the edifices were raised by means of earthen ramps, since machines for lifting had not yet been invented in those days; and most surprising it is, that although such large structures were raised in an area surrounded by sand, no trace remains of either ramps or the dressing of the stones, so that it seems not the result of the patient labor of men, but rather as if the whole complex were set down entire upon the surrounding sand by some god. Now Egyptians try to make a marvel of these things, alleging that the ramps were made of salt and natron and that, when the river was turned against them, it melted them clean away and obliterated their every trace without the use of human labor. But in truth, it most certainly was not done this way! Rather, the same multitude of workmen who raised the mounds returned the entire mass again to its original place; for they say that three hundred and sixty thousand men were constantly employed in the prosecution of their work, yet the entire edifice was hardly finished at the end of twenty years.

Diodorus Siculus's description of the shipment of the stone from Arabia is correct since the term "Arabia" in those days implied the land between the Nile and the Red Sea where the limestone blocks have been transported from quarries across the river Nile.

Materials

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Third through Fifth dynasties

During the earliest period, pyramids were constructed wholly of stone. Locally quarried limestone was the material of choice for the main body of these pyramids, while a higher quality of limestone quarried at Tura (near modern Cairo) was used for the outer casing. Granite, quarried near Aswan, was used to construct some architectural elements, including the portcullis (a type of gate) and the roofs and walls of the burial chamber. Occasionally, granite was used in the outer casing as well, such as in the Pyramid of Menkaure. In the early pyramids, the layers of stone (called courses) forming the pyramid body were laid sloping inwards; however, this configuration was found to be less stable than simply stacking the stones horizontally on top of each other. The Bent Pyramid at Dahshur seems to indicate acceptance of a new technique at a transition between these two building techniques. Its lower section is built of sloping courses while in its upper section the stones are laid horizontally.

Middle Kingdom and onward

During the Middle Kingdom, pyramid construction techniques changed again. Most pyramids built then were little more than mountains of mud-brick encased in a veneer of polished limestone. In several cases, later pyramids were built on top of natural hills to further reduce the volume of material needed in their construction. The materials and methods of construction used in the earliest pyramids have ensured their survival in a generally much better state of preservation than for the pyramid monuments of the later pharaohs.

Mortar

The stones forming the core of the pyramids were roughly cut, especially in the Great Pyramid. To fill the gaps, huge quantities of gypsum and rubble were needed. The filling has almost no binding properties, but it was necessary to stabilize the construction. To make the gypsum mortar, it had to be dehydrated by heating which requires large quantities of wood. According to Egyptologists, the findings of both the 1984 and 1995 David H. Koch Pyramids Radiocarbon Projects may suggest that Egypt had to strip its forest and scrap every bit of wood it had to build the pyramids of Giza and other even earlier 4th Dynasty pyramids. Carbon dating samples from core blocks and other materials revealed that dates from the 1984 study averaged 374 years earlier than currently accepted and the 1995 dating averaging 100–200 years. As suggested by team members, "We thought that it was unlikely that the pyramid builders consistently used centuries-old wood as fuel in preparing mortar. The 1984 results left us with too little data to conclude that the historical chronology of the Old Kingdom was wrong by nearly 400 years, but we considered this at least a possibility". Egyptologists propose that the old wood problem is responsible for the discrepancy, claiming the earlier dates were possibly derived from recycling large amounts of centuries-old wood and other earlier materials.

Quarrying

There is good information concerning the location of the quarries, some of the tools used to cut stone in the quarries, transportation of the stone to the monument, leveling the foundation, and leveling the subsequent tiers of the developing superstructure. Workmen probably used copper chisels, drills, and saws to cut softer stone, such as most of the limestone. The harder stones, such as granite, granodiorite, syenite, and basalt, cannot be cut with copper tools alone; instead, they were worked with time-consuming methods like pounding with dolerite, drilling, and sawing with the aid of an abrasive, such as quartz sand. This occurred in a process known as sand abrasion. Blocks were transported by sledge likely lubricated by water.

Leveling the foundation may have been accomplished by use of water-filled trenches as suggested by Mark Lehner and I. E. S. Edwards or through the use of a crude square level and experienced surveyors.

Transport of stone blocks

A transport of a large statue on a sledge

One of the major problems faced by the early pyramid builders was the need to move huge quantities of stone. The Twelfth Dynasty tomb of Djehutihotep has an illustration of 172 men pulling an alabaster statue of him on a sledge. The statue is estimated to weigh 60 tons and Denys Stocks estimated that 45 workers would be required to start moving a 16,300 kg (35,900 lb; 16.3 t) lubricated block, or eight workers to move a 2,750 kg (6,060 lb; 2.75 t) block. Dick Parry has suggested a method for rolling the stones, using a cradle-like machine that had been excavated in various new kingdom temples. Four of those objects could be fitted around a block so it could be rolled easily. Experiments done by the Obayashi Corporation, with concrete blocks 0.8 metres (2 ft 7 in) square by 1.6 metres (5 ft 3 in) long and weighing 2.5 tonnes (2,500 kg; 5,500 lb), showed how 18 men could drag the block over a 1-in-4 incline ramp, at a rate of 18 metres per minute (1 ft/s). This idea was previously described by John Bush in 1977, and is mentioned in the Closing Remarks section of Parry's book. Vitruvius in De architectura described a similar method for moving irregular weights. It is still not known whether the Egyptians used this method but the experiments indicate it could have worked using stones of this size. Egyptologists generally accept this for the 2.5 ton blocks mostly used but do not agree over the methods used for the 15+ ton and several 70 to 80 ton blocks.

The diary of Merer, logbooks written more than 4,500 years ago by an Egyptian official and found in 2013 by a French archeology team under the direction of Pierre Tallet in a cave in Wadi al-Jarf, describes the transportation of limestone blocks from the quarries at Tura to Giza by boat.

Ramps

Example of a large straight ramp. This method was likely not used in pyramid construction according to current expert consensus (see text).

From left to right: Zig-zagging ramp (Uvo Hölscher), ramp using the incomplete part of the superstructure (Dieter Arnold), and a spiraling ramp supported by the superstructure (Mark Lehner)

Most Egyptologists acknowledge that ramps are the most tenable of the methods to raise the blocks, yet they acknowledge that it is an incomplete method that must be supplemented by another device. Archaeological evidence for the use of ramps has been found at the Great Pyramid of Giza and other pyramids. The method most accepted for assisting ramps is levering. The archaeological record gives evidence of only small ramps and inclined causeways, not something that could have been used to construct even a majority of the monument. To add to the uncertainty, there is considerable evidence demonstrating that non-standardized or ad hoc construction methods were used in pyramid construction.

Therefore, there are many proposed ramps and there is a considerable amount of discrepancy regarding what type of ramp was used to build the pyramids. One of the widely discredited ramping methods is the large straight ramp, and it is routinely discredited on functional grounds for its massive size, lack of archaeological evidence, huge labor cost, and other problems (Isler 2001: 213).

Other ramps serve to correct these problems of ramp size, yet either run into critiques of functionality and limited archaeological evidence. There are zig-zagging ramps, straight ramps using the incomplete part of the superstructure (Arnold 1991), spiraling ramps supported by the superstructure and spiraling ramps leaning on the monument as a large accretion are proposed. Mark Lehner speculated that a spiraling ramp, beginning in the stone quarry to the southeast and continuing around the exterior of the pyramid, may have been used. However, spiral ramps would have covered the building for decades fully and would not allow the regular layout of the exact pyramid square in equal distance to each base cornerstone as the only method to keep the exact geometric shape of the edges and side mantles. The stone blocks may have been drawn on sleds along the ramps lubricated by water.

As a recent study shows that the challenge was not just to account for the route the transported stones had to take but to account for the size and frequency of stones being moved—circa 1 ton being put in place every 2–3 minutes by human draw teams on a ramp of maximum 10%—to enable building of the Great Pyramid within 30 years. The special case of the pyramid extensions E2 and E3 in Meydum of ring-shaped extensions only 5 m wide around the previous building core shows the ramp system was effective and small in volume which applies for tangential ramps of 10 cubits or 5m width. The challenge was the geometry of the pyramid that provides shorter side lengths the higher the building grows, increases the necessity to turn maneuvers and allows less space for ramps leaning on the masonry. The slope change of the Bent Pyramid is probably the result of the discovery this can not be solved with steep gradients. Essential was also the effective organization of the building site by a module that allows the work division of the teams along plots and the transport causeways between ramp and workplace, including the return of pulling crew and sleds down, probably by a second ramp system. The problem of building the mantle at the ramp arrival point could be solved by bypass-systems.

Levering

Levering methods are considered to be the most tenable solution to complement ramping methods, partially due to Herodotus's description; and partially to the shadoof, a lever-enabled irrigation device first depicted in Egypt during the New Kingdom and found concomitantly with the Old Kingdom in Mesopotamia. In Lehner's (1997: 222) point of view, levers should be employed to lift the top 3% of the material of the superstructure. It is important to note that the top 4% of this material comprises 1⁄3 of the total height of the monument. In other words, in Lehner's view, levers should be employed to lift a small amount of material and a great deal of vertical height of the monument.

In the milieu of levering methods, there are those that lift the block incrementally, as in repeatedly prying up alternating sides of the block and inserting wooden or stone shims to gradually move the stone up one course; and there are other methods that use a larger lever to move the block up one course in one lifting procedure. Since the discussion of construction techniques to lift the blocks attempts to resolve a gap in the archaeological and historical record with a plausible functional explanation, the following examples by Isler, Keable, and Hussey-Pailos list experimentally tested methods. Isler's method (1985, 1987) is an incremental method and, in the Nova experiment (1992), used wooden shims or cribbing. Isler was able to lift a block up one tier in approximately one hour and 30 minutes. Peter Hodges's and Julian Keable's method is similar to Isler's method and instead used small manufactured concrete blocks as shims, wooden pallets, and a pit where their experimental tests were performed. Keable was able to perform his method in approximately 2 minutes. Scott Hussey-Pailos's (2005) method uses a simple levering device to lift a block up a course in one movement. This method was tested with materials of less strength than historical analogs (tested with materials weaker than those available in ancient Egypt), a factor of safety of 2, and lifted a 2500-pound block up one course in under a minute. This method is presented as a levering device to work complementary with Mark Lehner's idea of a combined ramp and levering techniques.

Harbors

Egyptians used the now-disappeared branch of the Nile to transport the tons of construction materials. A 2012 study led by geographer Hader Sheisha at Aix-Marseille University proposed that the former waterscapes and higher river levels around 4,500 years ago facilitated the construction of the Giza Pyramid Complex. The Nile's present waterways have receded too far from the pyramid sites to be of use.

A new study published in May 2024 mapped an extinct branch of the Nile, Ahramat Branch, which once flowed near Egypt's Great Pyramid and other Giza monuments. Using satellite imaging and sediment core analysis, researchers found the 64 kilometres (40 mi) waterway was crucial for transporting materials and labor for pyramid construction. The branch which was about 0.5 kilometres (0.31 mi) wide with a depth of at least 25 metres (82 ft) disappeared likely due to drought and desertification.

Pyramid building experiments

Yoshimura

In 1978, Nippon TV funded the pyramid building project conceived by archaeologist Sajuki Yoshimura. It was originally planned as a 1 to 5 scale model of the Great Pyramid. Because of the limited budget, the size had to be drastically reduced when the price of limestone rose as the project gained publicity. A concrete foundation had to be poured as the selected site offered no bedrock basis. With the help of two cranes and a forklift, the pyramid was built to reach a height of 11 metres (36 ft), with a 15 metres (49 ft) base. The structure was ultimately dismantled and hauled away.

Nova

In 1992, Egyptologist Mark Lehner and stonemason Roger Hopkins conducted a three-week pyramid-building experiment for a Nova television episode. They built a pyramid 6 metres (20 ft) high by 9 metres (30 ft) wide, consisting of a total of 162 cubic metres (5,700 cu ft), or about 405 tons. It was made out of 186 stones weighing an average of 2.2 tons each. Twelve quarrymen carved 186 stones in 22 days, and the structure was erected using 44 men. They used iron hammers, chisels and levers (this is a modern shortcut, as the ancient Egyptians were limited to using copper and later bronze and wood). But Lehner and Hopkins did experiments with copper tools, noting that they were adequate for the job in hand, provided that additional manpower was available to constantly resharpen the ancient tools. They estimated they would have needed around 20 extra men for this maintenance. Another shortcut taken was the use of a front-end loader or fork lift truck, but modern machinery was not used to finish the construction. They used levers to lift the capstone to a height of 20 feet (6.1 m). Four or five men were able to use levers on stones less than one ton to flip them over and transport them by rolling, but larger stones had to be towed. Lehner and Hopkins found that by putting the stones on wooden sledges and sliding the sledges on wooden tracks, they were able to tow a two-ton stone with 12 to 20 men. The wood for these sledges and tracks would have to have been imported from Lebanon at great cost since there was little, if any, wood in ancient Egypt. While the builders failed to duplicate the precise jointing created by the ancient Egyptians, Hopkins was confident that this could have been achieved with more practice.

Great Pyramid

Further information: Diary of Merer

Some research suggests other estimates to the accepted workforce size. For instance, physicist Kurt Mendelssohn calculated that the workforce may have been 50,000 men at most, while Ludwig Borchardt and Louis Croon placed the number at 36,000. According to Miroslav Verner, a workforce of no more than 30,000 was needed in the Great Pyramid's construction. Evidence suggests that around 5,000 were permanent workers on salaries with the balance working three- or four-month shifts in lieu of taxes while receiving subsistence "wages" of ten loaves of bread and a jug of beer per day. Zahi Hawass believes that the majority of workers may have been volunteers. Most archaeologists agree that only about 4,000 of the total workforce were labourers who quarried the stone, hauled blocks to the pyramid, and set the blocks in place. The vast majority of the workforce provided support services such as scribes, toolmakers, and other backup services. The tombs of supervisors contain inscriptions regarding the organisation of the workforce. There were two crews of approximately 2,000 workers sub-divided into named gangs of 1,000. The gangs were divided into five phyles of 200 which were in turn split into groups of around 20 workers grouped according to their skills, with each group having their own project leader and a specific task.

A construction management study carried out by the firm Daniel, Mann, Johnson, & Mendenhall in association with Mark Lehner, and other Egyptologists, estimates that the total project required an average workforce of 14,567 people and a peak workforce of 40,000. Without the use of pulleys, wheels, or iron tools, they used critical path analysis to suggest the Great Pyramid was completed from start to finish in approximately 10 years. Their study estimates the number of blocks used in construction was between 2 and 2.8 million (an average of 2.4 million), but settles on a reduced finished total of 2 million after subtracting the estimated volume of the hollow spaces of the chambers and galleries. Most sources agree on this number of blocks somewhere above 2.3 million. Their calculations suggest the workforce could have sustained a rate of 180 blocks per hour (3 blocks/minute) with ten-hour workdays for putting each individual block in place. They derived these estimates from modern third-world construction projects that did not use modern machinery, but conclude it is still unknown exactly how the Great Pyramid was built. As Dr. Craig Smith of the team points out:

The logistics of construction at the Giza site are staggering when you think that the ancient Egyptians had no pulleys, no wheels, and no iron tools. Yet, the dimensions of the pyramid are extremely accurate and the site was leveled within a fraction of an inch over the entire 13.1-acre base. This is comparable to the accuracy possible with modern construction methods and laser leveling. That's astounding. With their 'rudimentary tools', the pyramid builders of ancient Egypt were about as accurate as we are today with 20th-century technology.

Average core blocks of the Great Pyramid weigh about 1.5 tons each, and the granite blocks used to roof the burial chambers are estimated to weigh up to 80 tons each.

The entire Giza Plateau is believed to have been constructed over the reign of five pharaohs in less than a hundred years, which generally includes: the Great Pyramid, Khafre and Menkaure's pyramids, the Great Sphinx, the Sphinx, and Valley Temples, 35 boat pits cut out of solid bedrock, and several causeways, as well as paving nearly the entire plateau with large stones. This does not include Khafre's brother Djedefre's northern pyramid at Abu Rawash, which would have also been built during this time frame of 100 years. In the hundred years prior to Giza—beginning with Djoser, who ruled from 2687 to 2667 BC, and amongst dozens of other temples, smaller pyramids, and general construction projects—four other massive pyramids were built: the Step pyramid of Saqqara (believed to be the first Egyptian pyramid), the pyramid of Meidum, the Bent Pyramid, and the Red Pyramid. Also during this period (between 2686 and 2498 BC) the Sadd el-Kafara dam, which used an estimated 100,000 cubic meters of rock and rubble, was built.

In October 2018, a team of archaeologists from the Institut Français d'Archéologie Orientale and University of Liverpool announced the discovery of the remains of a 4,500-year-old ramp contraption at Hatnub, excavated since 2012. This method, which aided in lifting the heavy alabaster stones up from their quarries, may have been used to build Egypt's Great Pyramid as well. Yannis Gourdon, co-director of the joint mission at Hatnub, said:

This system is composed of a central ramp flanked by two staircases with numerous post holes, using a sled which carried a stone block and was attached with ropes to these wooden posts, ancient Egyptians were able to pull up the alabaster blocks out of the quarry on very steep slopes of 20 percent or more ... As this system dates back at least to Khufu's reign, that means that during the time of Khufu, ancient Egyptians knew how to move huge blocks of stone using very steep slopes. Therefore, they could have used it for the construction [of] his pyramid.

Internal ramp hypothesis

Main article: Jean-Pierre Houdin

Houdin's father was an architect who, in 1999, thought of a construction method that, it seemed to him, made more sense than any existing method proposed for building pyramids. To develop this hypothesis, Jean-Pierre Houdin, also an architect, gave up his job and set about drawing the first fully functional CAD architectural model of the Great Pyramid of Giza. His scheme involves using a regular external ramp to build the first 30% of the pyramid, with an "internal ramp" taking stones up beyond that height. The stones of the external ramp are re-cycled into the upper stories, thus explaining the otherwise puzzling lack of evidence for ramps.

After four years working alone, Houdin was joined by a team of engineers from the French 3D software company Dassault Systèmes, who used the most modern computer-aided design technology available to further refine and test the hypothesis, making it (according to Houdin) the only one proven to be a viable technique. Houdin published his theory in the books Khufu: The Secrets Behind the Building of the Great Pyramid in 2006 and The Secret of the Great Pyramid, co-written in 2008 with Egyptologist Bob Brier.

In Houdin's method, each ramp inside the pyramid ended at an open space, a notch temporarily left open in the edge of the construction. This 10-square-meter clear space housed a crane that lifted and rotated each 2.5-ton block, to ready it for eight men to drag up the next internal ramp. There is a notch of sorts in one of the right places, and in 2008 Houdin's co-author Bob Brier, with a National Geographic film crew, entered a previously unremarked chamber that could be the start of one of these internal ramps. In 1986 a member of the French team (see below) saw a desert fox at this notch, rather as if it had ascended internally.

Houdin's thesis remains unproven and in 2007, Egyptologist David Jeffreys from the University College London described the internal spiral hypothesis as "far-fetched and horribly complicated", while Oxford University's John Baines, declared he was "suspicious of any theory that seeks to explain only how the Great Pyramid was built".

Houdin has another hypothesis developed from his architectural model, one that could finally explain the internal "Grand Gallery" chamber that otherwise appears to have little purpose. He believes the gallery acted as a trolley chute/guide for counterbalance weights. It enabled the raising of the five 60-ton granite beams that roof the King's Chamber. Houdin and Brier and the Dassault team are already credited with proving for the first time that cracks in beams appeared during construction, were examined and tested at the time and declared relatively harmless.