понедельник, 10 июня 2019 г.

Most-detailed-ever simulations of black hole solve longstanding mystery

An international team has constructed the most detailed, highest resolution simulation of a black hole to date. The simulation proves theoretical predictions about the nature of accretion disks — the matter that orbits and eventually falls into a black hole — that have never before been seen.

Most-detailed-ever simulations of black hole solve longstanding mystery
This image shows how the inner region of the accretion disk (red) aligns with the equatorial plane of the black hole.
The outer disk is tilted away. The inner disk (where the black curve dips) is horizontal, signaling the long-sought
Bardeen-Petterson alignment [Credit: Sasha Tchekhovskoy/Northwestern University;
Matthew Liska/University of Amsterdam]

Among the findings, the team of computational astrophysicists from Northwestern University, the University of Amsterdam and the University of Oxford found that the inner-most region of an accretion disk aligns with its black hole’s equator.

This discovery solves a longstanding mystery, originally presented by Nobel Prize-winning physicist John Bardeen and astrophysicist Jacobus Petterson in 1975. At the time, Bardeen and Petterson argued that a spinning black hole would cause the inner region of a tilted accretion disk to align with its black hole’s equatorial plane.

After a decades-long, global race to find the so-called Bardeen-Petterson effect, the team’s simulation found that, whereas the outer region of an accretion disk remains tilted, the disk’s inner region aligns with the black hole. A smooth warp connects the inner and outer regions. The team solved the mystery by thinning the accretion disk to an unprecedented degree and including the magnetized turbulence that causes the disk to accrete. Previous simulations made a substantial simplification by merely approximating the effects of the turbulence.

«This groundbreaking discovery of Bardeen-Petterson alignment brings closure to a problem that has haunted the astrophysics community for more than four decades,» said Northwestern’s Alexander Tchekhovskoy, who co-led the research. «These details around the black hole may seem small, but they enormously impact what happens in the galaxy as a whole. They control how fast the black holes spin and, as a result, what effect black holes have on their entire galaxies.»

Tchekhovskoy is an assistant professor of physics and astronomy in Northwestern’s Weinberg College of Arts and Sciences and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics), an endowed research center at Northwestern focused on advancing astrophysics studies with an emphasis on interdisciplinary connections. Matthew Liska, a researcher at the University of Amsterdam’s Anton Pannenkoek Institute for Astronomy, is the paper’s first author.

«These simulations not only solve a 40-year-old problem, but they have demonstrated that, contrary to typical thinking, it is possible to simulate the most luminous accretion disks in full general relativity,» Liska said. «This paves the way for a next generation of simulations, which I hope will solve even more important problems surrounding luminous accretion disks.»

Elusive alignment

Nearly everything researchers know about black holes has been learned by studying accretion disks. Without the intensely bright ring of gas, dust and other stellar debris that swirls around black holes, astronomers would not be able to spot a black hole in order to study it. Accretion disks also control a black hole’s growth and rotation speed, so understanding the nature of accretion disks is key to understanding how black holes evolve and function.

«Alignment affects how accretion disks torque their black holes,» Tchekhovskoy said. «So it affects how a black hole’s spin evolves over time and launches outflows that impact the evolution of their host galaxies.»

Simulation shows the inner region of the accretion disk aligns with the black hole’s equatorial plane, signaling the 

long-sought Bardeen-Petterson alignment [Credit: Sasha Tchekhovskoy/Northwestern University; 

Matthew Liska/University of Amsterdam]

From Bardeen and Petterson until present day, simulations have been too simplified to find the storied alignment. Two main issues have acted as a barrier for computational astrophysicists. For one, accretion disks come so close to the black hole that they move through warped space-time, which rushes into the black hole at immense speed. Complicating matters further, the black hole’s rotation forces space-time to spin around it. Properly accounting for both of these crucial effects requires general relativity, Albert Einstein’s theory that predicts how objects affect the geometry of space-time around them.

Second, astrophysicists have not had computing power to account for magnetic turbulence, or the stirring inside of the accretion disk. This stirring is what causes the disk’s particles to hold together in a circular shape and what causes gas eventually to fall into the black hole.

«Imagine you have this thin disk. Then, on top of that, you have to resolve the turbulent motions inside the disk,» Tchekhovskoy said. «It becomes a really difficult problem.»

Without being able to resolve these features, computational scientists were unable to simulate realistic black holes.

Cracking the code

To develop a code capable of carrying out simulations of titled accretion disks around black holes, Liska and Tchekhovskoy used graphical processing units (GPUs) instead of central processing units (CPUs). Extremely efficient at manipulating computer graphics and image processing, GPUs accelerate the creation of images on a display. They are much more efficient than CPUs for computing algorithms that process large swaths of data.

Tchekhovskoy likens GPUs to 1,000 horses and CPUs to a 1,000-horsepower Ferrari.

«Let’s say you need to move into a new apartment,» he explained. «You will have to make a lot of trips with this powerful Ferrari because it won’t fit many boxes. But if you could put one box on each horse, you could move everything in one go. That’s the GPU. It has a lot of elements, each of which is slower than those in the CPU, but there are so many of them.»

Liska also added a method called adaptive mesh refinement, which uses a dynamic mesh, or grid, that changes and adapts to the flow of movement throughout the simulation. It saves energy and computer power by focusing only on specific blocks in the grid where movement occurs.

The GPUs substantially accelerated the simulation, and the adaptive mesh increased resolution. These improvements allowed the team to simulate the thinnest accretion disk to date, with a height-to-radius ratio of 0.03. When the disk was simulated this thin, the researchers could see alignment occur right next to the black hole.

«The thinnest disks simulated before had a height-to-radius ratio of 0.05, and it turns out that all of the interesting things happen at 0.03,» Tchekhovskoy said.

In a surprise finding, even with these incredibly thin accretion disks, the black hole still emitted powerful jets of particles and radiation.

«Nobody expected jets to be produced by these disks at such slight thicknesses,» Tchekhovskoy said. «People expected that the magnetic fields that produce these jets would just rip through these really thin disks. But there they are. And that actually helps us resolve observational mysteries.»

The research was published in the Monthly Notices of the Royal Astronomical Society.

Source: Northwestern University [June 05, 2019]



Collapse and resilience of Levant communities during the Early Bronze Age

The system of centralised, urbanised settlements established in agriculturally productive valleys and plans broke down in the southern Levant around 2,500-1,950 BC, during the Early Bronze (EB) Age IV, noted an American archaeologist.

Collapse and resilience of Levant communities during the Early Bronze Age
Tell Umayri outside of Amman with what is left on the site’s surface,
winter 2019 [Credit: Amy Karoll]

“Previous theories imply that this breakdown coincided with a major climatological event: a widespread drought that occurred around 2,200 BC across the ancient Near East. According to this theory, a series of crises in the Near East occurred over a century, first affecting semi-arid regions along agricultural margins in northern Mesopotamia and moved towards the eastern margins of the Levant,” explained Amy Karoll, adding that settlements along river systems were less affected due to access to water that was not dependent on rainfall.

Since this environmentally deterministic theory was first proposed, she continued, a new data has called into question the timing of the EB IV decline. As such, “collapse” may no longer be a valid model to analyse this period, Karoll said, and, instead, she proposed investigating “alternative explanations that situate people as active agents in a resilient socioeconomic system”.

“The changes in economic and political systems were conscious choices, shaped and limited by outside factors,” the scholar underlined, noting that rather than a sudden collapse of society due to catastrophic climatic change, disrupting agricultural production, it appears that the EB IV transition was the logical consequence of people actively responding to their steadily changing environment.

Karoll, who is a PhD candidate at the University of California Los Angeles in Near Eastern Languages and Cultures, has studied sites of the Jordan Valley.

According to her, the main site is Khirbet Iskander, located on the central Transjordanian Plateau, some 24km south of Madaba and right off the King’s Highway.

“The EB IV occupation is particularly important at the site: Khirbet Iskander was a fortified, sedentary town during the EB IV, one of very few. Another is Bab edh-Dhra, located near the Dead Sea on the Karak Plateau,” she noted, adding that she also looked at Tell Al Hammam and Tell Iktanu in the Jordan Valley, Khirbet Al Batrawy, northeast of Amman, and Tell Al Umayri on the road to the airport.

Trade connections between sites in east and west banks had been well known as Tell Al Hammam on the eastern side and Jericho on the western side had very close trade connections during the EB IV, Karoll claimed.

“Previous ideas of a purely nomadic society, first proposed in the mid-20th century, have been shown to be a fallacy,” the researcher said. She pointed out that agriculture is either integrated into seasonal rounds of pastoral groups or trade is required to provide these goods.

Furthermore, societies incorporated both modes of economy, Karoll said, adding that her study will not address urban agriculturalists and pastoral nomads as a dichotomy, but rather attempt to situate these concepts along a spectrum, where each is reliant upon the other.

Variations within pastoral systems, especially as they change over time during the late third millennium BC, will be addressed in order to identify the impact pastoral nomads had on economic, social and political regimes of this period, she stressed.

Her future plans regarding a dissertation research is to use this research as a means to study collapse and resilience in the entirety of the southern Levant.

“The EB IV is not the only period of ‘collapse’ and change in the Levant. These changes occur at every major period transition, from the Middle to the Late Bronze Age, from the Late Bronze Age to the Iron Age, etc,” Karoll underscored.

Author: Saeb Rawashdeh | Source: The Jordan Times [June 05, 2019]



Shaking up the sloth family tree

New studies by two research teams published today in the journals Nature Ecology and Evolution and Current Biology challenge decades of accepted scientific opinion concerning the evolutionary relationships of tree sloths and their extinct kin. The research teams used different molecular tools—the protein collagen in one case and the mitochondrial genome in the other—but they reached nearly the same results. The concurrent findings are significant because they provide molecular evidence that appears to overturn a longstanding consensus, based on the study of anatomical features, regarding how the major groups of sloths are related to one another.

Shaking up the sloth family tree
In the tree, going clockwise from left: extinct West Indian sloth (Acratocnus), extant three-toed sloth or ai (Bradypus),
and extant two-toed sloth or unau (Choloepus). From left to right on the ground are representative giant ground
sloths: Mylodon (South America), Megalonyx (North America), and Megatherium (South America).
According to new molecular studies, Bradypus is most closely related to a group that includes Megalonyx
and Megatherium. Choloepus is related to Mylodon, but Acratocnus and its West Indian kin represent
 a separate branch that is distinct from that of all other sloths. Human for scale: 1.8.5 m (6 ft 1 in)
[Credit: Jorge Blanco]

Corresponding authors Ross D. E. MacPhee of the American Museum of Natural History and Frédéric Delsuc of the French National Centre for Scientific Research (CNRS) at the University of Montpellier noted that, although their research groups worked separately, they were in communication.

«All of us were initially surprised by our results because they thoroughly contradicted what seemed to be the accepted view based on anatomy,» said Delsuc.

«Exceptional results demand exceptional verification,» continued MacPhee, a curator in the Museum’s Department of Mammalogy, «That’s why we arranged with the journals to publish our papers simultaneously, to emphasize that corroboration is a crucial part of good science.»

To undertake their work, the teams had to collect molecular information not only from the two kinds of living tree sloths—the unau, in the genus Choloepus (also known as two-toed sloths) and the ai, in the genus Bradypus (three-toed sloths)—but also a wide range of extinct forms, including the large ground sloths, which can be seen on exhibition in many natural history museums.

Delsuc’s team targeted the DNA housed in mitochondria, the cellular «energy engines» that exist in large numbers in the body’s tissues and can be recovered using ancient DNA capture methods from well-preserved fossil material. Compared to the nuclear genome, however, the information that the mitochondrial genome contains is limited and may sometimes be incongruent with evolutionary history.

Importantly, findings from the other team’s study, which analyzed the protein collagen, closely agreed with the mitochondrial study. Paleoproteomics, or the utilization of protein evidence for taxonomic purposes, is a relatively new field, but type 1 («bone») collagen has become an increasingly important source of information in mammalian paleontology, for two reasons: it degrades more slowly than DNA, and it can be found in large amounts in well-preserved fossils because it makes up 80-90 percent of the organic fraction of bone.

The genes providing the instructions for the synthesis of bone collagen reside in the nucleus, and because of the precise relationship between the building blocks of a given gene and the protein for which it codes, the protein’s amino acids reflect information present in the gene at the DNA level. Thus, between them the two studies sampled both parts of the genome, nuclear as well as mitochondrial.

Shaking up the sloth family tree
A photo of a fossil of Lestodon, a mylodontoid ground sloth
from South America [Credit: AMNH/D. Finnin]

«Structural proteins like collagen potentially last much, much longer after death than the relatively fragile DNA molecule,» said Samantha Presslee, the lead author on the Nature Ecology and Evolution paper and a doctoral student at the University of York. «This means that scientists can extract and interpret protein evidence from a wide range of extinct species well beyond the current reach of ancient DNA.»

Other proteomic investigations have reported high-quality collagen from specimens as old as 3.8 million years, from an island in the Canadian Arctic. In the case of the sloth study, the oldest successful recovery was from a fossil between 120,000 and 400,000 years old; older specimens were tried but did not yield useful information.

«Having the results of both sources of molecular information in front of us, we knew that we were standing on solid ground, and that it was time to revisit sloth evolution and classification,» said Hendrik Poinar of the Ancient DNA Centre at McMaster University, who was also a corresponding author on the mitogenomic paper.

With their long arms, hook-like claws, and upside-down locomotion the six species of living tree sloths seem remarkably similar, but research has shown that they gained their adaptations for life in the trees independently through a phenomenon known as evolutionary convergence. Convergent origins were also supported by the molecular investigations, but most other inferences about sloth evolutionary relationships were not.

For example, the ais (three-toed sloths) have long been regarded as being so anatomically different from other sloths that they were classified on a completely separate evolutionary branch. Both the mitochondrial and protein evidence indicate that this view is not correct: Bradypus folds well within Megatherioidea, a group that also included the largest of all sloths, the elephant-sized giant ground sloth Megatherium.

Similarly, the unaus (two-toed sloths) were found to be members of another major group called the mylodontoids, although they had previously been placed in Megalonychidae, a family originally defined to include the extinct North American ground sloth Megalonyx and a number of island species that lived in the West Indies until a few thousand years ago.

Shaking up the sloth family tree
A photo of a fossil of Megalonyx, a megatherioid ground sloth
from North America [Credit: AMNH/D. Finnin]

Each team also attempted molecular dating to interpret their evidence in the context of the sloth fossil record in order to make predictions about when the different major groups separated from one another. This led to another major surprise: the combined molecular evidence suggests that the West Indian sloths, known as megalocnids, diverged from the ancestor of both megatherioids and mylodontoids more than 30 million years ago.

The first sloths to reach the Greater Antilles may have entered over a temporary land connection between these islands and South America. In taxonomic terms, that makes them the closest relatives or sister group of all other sloths, whereas they had previously been regarded as a minor, late-evolving group within the megatherioid radiation. Another finding at odds with traditional taxonomy is that Megalonyx, previously thought to be a close relative of the unau (two-toed sloth), appears to be more closely related to the ai (three-toed sloth).

«The combined molecular results are surprising on many levels,» said Graham Slater, an assistant professor of geophysical sciences at the University of Chicago, who was involved in the protein paper. «Not only do they rewrite sloth classification, they suggest much of what we thought we knew about how sloths evolved may be wrong. We’ve been used to thinking that today’s sloths evolved independently for life in the trees from a ground-dwelling ancestor, but our results suggest that the basal, or ancestral, sloth may have been at home in both.»

One reason for this thinking is that most of the West Indian sloths appear to have been highly arboreal, with some showing adaptations quite similar to those of the living tree sloths.

«Although the molecular results conflict with current paleontological views based on anatomical features, there can be only one history of life,» said MacPhee. «The job now is to reconcile these differing methods of inference, which means a lot more work on everyone’s part. We are going to learn a lot, and that’s exciting.»

«Until recently, extinct organisms could only be included in genealogical analyses of living organisms by using data based on their morphology or appearance,» said Simon Malcomber, a program director at the National Science Foundation, which funded the paleoproteomic research. «This research shows how the combined molecular analyses of extinct and living relatives can provide surprising—and exciting—new insights into how life on Earth has evolved. These new extraction methods open the door to fresh examination of relationships between living and extinct organisms, and how the diversity of life has changed over time.»

Source: American Museum of Natural History [June 06, 2019]



‘Rudston Monolith’ Prehistoric Standing Stone, Rudston, Yorkshire,…

‘Rudston Monolith’ Prehistoric Standing Stone, Rudston, Yorkshire, 9.6.19.

Britain’s tallest standing stone at 26ft high and thought to be buried to an equal depth underground.

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2019 June 10 Jupiter Abyss Image Credit: NASA, Juno, SwRI,…

2019 June 10

Jupiter Abyss
Image Credit: NASA, Juno, SwRI, MSSS; Processing & License: Gerald Eichstädt & Sean Doran

Explanation: What’s that black spot on Jupiter? No one is sure. During the latest pass of NASA’s Juno around Jupiter, the robotic spacecraft imaged an usually dark cloud feature informally dubbed the Abyss. Surrounding cloud patterns show the Abyss to be at the center of a vortex. Since dark features on Jupiter’s atmosphere tend to run deeper than light features, the Abyss may really be the deep hole that it appears – but without more evidence that remains conjecture. The Abyss is surrounded by a complex of meandering clouds and other swirling storm systems, some of which are topped by light colored, high-altitude clouds. The featured image was captured last month while Juno passed only about 15,000 kilometers above Jupiter’s cloud tops. The next close pass of Juno near Jupiter will be in July.

∞ Source: apod.nasa.gov/apod/ap190610.html

Space Station Science Highlights: Week of June 3, 2019

ISS — Expedition 59 Mission patch.

June 9, 2019

The members of Expedition 59 conducted scientific investigations on the International Space Station last week that included studies on physical and psychological adaptation to space and protection from radiation exposure. These and many other space station investigations support NASA’s goal of returning humans to the Moon by 2024 as part of its Artemis human exploration program, as well as the goal of ongoing commercialization of the orbiting lab.

International Space Station (ISS). Image Credit: NASA

Here are details on some of the scientific investigations conducted during the week of June 3:

Assessing astronaut adaptation to space

Behavioral Core Measures (BCM) investigates the use of a standard set of measurements to assess adverse cognitive or behavioral conditions and psychiatric disorders during long-duration spaceflight. Following up on testing in ground analog studies, the flight investigation evaluates the feasibility of using this set of measurements within the operational and time constraints of spaceflight. Two crew members completed a questionnaire for BCM last week. The crew also completed questionnaires and saliva collection for Standard Measures, an effort to characterize adaptive responses to and risks of living in space consistently throughout the space station program.

Image above: NASA astronaut Nick Hague places samples into the General Laboratory Active Cryogenic International Space Station (ISS) Experiment Refrigerator (GLACIER), which store scientific samples at temperatures as low as -160 °C (-301 °F). Image Credit: NASA.

Protecting space explorers from radiation

The crew retrieved Radi-N2 bubble detectors and deployed additional detectors in the Cupola, sleeping area, and a wearable pouch. This Canadian Space Agency investigation seeks to better characterize the space station’s neutron radiation environment, define the risk posed to the health of crew members, and provide data to develop advanced protective measures for future spaceflight. Neutrons make up a significant fraction of the biologically effective radiation exposure in low-Earth orbit. The bubble detectors detect neutrons and ignore all other radiation types.

Image above: NASA astronaut Christina Koch in the vestibule between the SpaceX Dragon cargo craft and the Harmony module prior to closing the hatch for release of Dragon for its return to Earth. Dragon spent nearly a month attached to the International Space Station. Image Credit: NASA.

Charting cardiovascular changes

The crew participated in a Vascular Echo session including arterial blood pressure measurements and ultrasound scans of the neck, thigh, portal vein and heart. Some crew members return from the space station with much stiffer arteries than when they went into space. This investigation examines changes in blood vessels and the heart in space and after return to Earth. The results could provide insight into potential countermeasures to help keep astronauts healthy on long space missions, as well as improve quality of life for people on Earth.

Image above: The SpaceX Dragon cargo craft after undocking from the space station and moments before its release from the Canadarm2 robotic arm on Monday, May 3, 2019. The orbiting lab was flying 261 miles above central Asia at the time. Image Credit: NASA.

Other investigations on which the crew performed work:

— The Astrobee free-flying robots test technology for assisting astronauts with routine chores and giving ground controllers additional eyes and ears on the space station: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Facility.html?#id=1891

— The Photobioreactor investigation demonstrates whether the biological processes of microalgae can serve as part of a hybrid life support system. This approach would help future long-duration exploration missions reduce the amount of supplies required from Earth: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7426

— Residual Momentum and Tank Dynamics in Microgravity Environment (Furphy) tests the transfer of fluids from a rigid to a collapsible tank that expands as it fills. This capability supports future space exploration by making it possible to fuel small spacecraft in orbit instead of prior to launch, potentially saving launch mass and volume: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7842

— The ISS Experience documents daily life aboard the space station through a virtual reality film to educate a variety of audiences about life in the orbiting lab and science conducted there: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7877

— Veggie PONDS uses a newly developed passive nutrient delivery system and the Veggie Cell plant growth facility to cultivate lettuce and greens on the space station for on-orbit consumption and analysis on Earth: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7581

— Veg-04 focuses on how light quality and fertilizer affect growth of a leafy crop, along with microbial food safety, nutritional value, taste acceptability by the crew, and the overall behavioral health benefits of having plants and fresh food in space: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7896

— FLUIDICS uses a sphere in microgravity to represent a spacecraft’s fuel tank in order to analyze slosh and wave turbulence of a fluid. Results could support development of better fuel systems for satellites and future spacecraft: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=2043

Space to Ground: Release the Dragon: 06/07/2019

Related links:

Expedition 59: https://www.nasa.gov/mission_pages/station/expeditions/expedition59/index.html

Artemis: https://www.nasa.gov/feature/what-is-artemis/

Behavioral Core Measures (BCM): https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7537

Standard Measures: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7711

Radi-N2: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=874

Vascular Echo: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=1664

Spot the Station: https://spotthestation.nasa.gov/

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Video (NASA), Text, Credits: NASA/Michael Johnson/Jorge Sotomayor, Lead Increment Scientist Expeditions 59/60.

Best regards, Orbiter.chArchive link

Vivianite | #Geology #GeologyPage #Mineral Locality: Huanuni…

Vivianite | #Geology #GeologyPage #Mineral

Locality: Huanuni Mine, Oruro Department, Bolivia

Size: 4.8 × 4 × 2.3 cm

Photo Copyright © blue mountains /e-rocks. com

Geology Page



Demantoid | #Geology #GeologyPage #Mineral Locality: Erongo…

Demantoid | #Geology #GeologyPage #Mineral

Locality: Erongo Mountains, Erongo Region, Namibia

Size: 1.6 × 1.3 × 1.1 cm

Photo Copyright © Viamineralia /e-rocks. com

Geology Page



Study provides new insight into origin of Canadian Rockies…

Study provides new insight into origin of Canadian Rockies http://www.geologypage.com/2019/06/study-provides-new-insight-into-origin-of-canadian-rockies.html

New findings on Earth’s magnetic field…

New findings on Earth’s magnetic field http://www.geologypage.com/2019/06/new-findings-on-earths-magnetic-field.html

How deep-ocean vents fuel massive phytoplankton blooms…

How deep-ocean vents fuel massive phytoplankton blooms http://www.geologypage.com/2019/06/how-deep-ocean-vents-fuel-massive-phytoplankton-blooms.html

‘Danes Dyke’ Neolithic Earthworks Photoset 1, Flamborough Head, Yorkshire,...

‘Danes Dyke’ Neolithic Earthworks Photoset 1, Flamborough Head, Yorkshire, 9.6.19.

A massive prehistoric earthworks comprising a ditch and mound, running for over 13km and effectively isolating the headland. It is defensive but of unknown specific context.

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‘Danes Dyke’ Neolithic Earthworks Photoset 2, Flamborough Head, Yorkshire,...

‘Danes Dyke’ Neolithic Earthworks Photoset 2, Flamborough Head, Yorkshire, 9.6.19.

A massive 13km stretch of earthworks comprising huge banks and a steep ditch.

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    Солнечное затмение 14 декабря 2020 года  — полное  солнечное затмение  142  сароса , которое лучше всего будет видно в юго-восточной час...