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- Construction began 2800 B.C.
- Location: Wiltshire, England
- Purpose remains controversial but the center was carefully aligned in order to clearly view the summer solstices it helped predict the eclipses

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The stones of Stonehenge have endured centuries of weathering and erosion.

Credit: ivanovsky | Shutterstock

Stonehenge is a massive stone monument located on a chalky plain north of the modern-day city of Salisbury, England. Research shows that the site has continuously evolved over a period of about 10,000 years. The structure that we call "Stonehenge" was built between roughly 5,000 and 4,000 years ago and was one part of a larger sacred landscape that included a massive stone monument that was 15 times the size of Stonehenge.

The biggest of Stonehenge's stones, known as sarsens, are up to 30 feet (9 meters) tall and weigh 25 tons (22.6 metric tons) on average. It is widely believed that they were brought from Marlborough Downs, a distance of 20 miles (32 kilometers) to the north.

Smaller stones, referred to as "bluestones" (they have a bluish tinge when wet or freshly broken), weigh up to 4 tons and come from several different sites in western Wales, having been transported as far as 140 miles (225 km). It's unknown how people in antiquity moved them that far. Recent experiments show that it is possible for a one-ton stone to be moved by a dozen people on a wooden trackway, but whether this technique was actually used by the ancient builders is uncertain.

Scientists have also raised the possibility that during the last ice age glaciers carried these bluestones closer to the Stonehenge area and the monument's makers didn't have to move them all the way from Wales. Water transport by raft is another idea that has been proposed but researchers now question whether this method was viable.

No one knows why ancient people built Stonehenge, but it seems to have been arranged to face the midsummer sunrise and midwinter sunset.

Credit: Pete Strasser nasa.gov

Stonehenge is just one part of a larger sacred landscape that contains many other stone and wooden structures as well as burials. Archaeologists have also found evidence for widespread prehistoric hunting and a road that may have led to Stonehenge.

From what scientists can tell, Salisbury Plain was considered to be a sacred area long before Stonehenge itself was constructed. As early as 10,500 years ago, three large pine posts, which were totem poles of sorts, were erected at the site.

Hunting played an important role in the area. Researchers have uncovered roughly 350 animal bones and 12,500 flint tools or fragments, just a mile away from Stonehenge, the finds dating from 7500 B.C. to 4700 B.C. The presence of abundant game may have led people to consider the area sacred.

Dozens of burial mounds have been discovered near Stonehenge indicating that hundreds, if not thousands, of people were buried there in ancient times. At least 17 shrines, some in the shape of a circle, have also been discovered near Stonehenge. A " House of the Dead" was recently discovered near Stonehenge that dates to 3700 B.C.-3500 B.C.

Around 5,500 years ago two earthworks known as Cursus monuments were erected at Stonehenge, the longest of which ran for 1.8 miles (3 km). By 5,300 years ago two massive eyeglass-shaped wooden palisades, which were set ablaze during ceremonies, were constructed at Avebury, near Stonehenge.

At Stonehenge, more construction occurred around 5,000 years ago with postholes indicating that either bluestones or upright timber posts were propped up on the site. Then, around 4,600 years ago, a double circle made using dozens of bluestones was created at the site.

By 4,400 years ago, Stonehenge had changed again, having a series of sarsen stones erected in the shape of a horseshoe, with every pair of these huge stones having a stone lintel connecting them. In turn, a ring of sarsens surrounded this horseshoe, their tops connecting to each other, giving the appearance of a giant interconnected stone circle surrounding the horseshoe.

By 4,300 years ago, Stonehenge had been expanded to include the addition of two bluestone rings, one inside the horseshoe and another between the horseshoe and the outer layer of interconnected sarsen stones.

Construction at Stonehenge slowed down around 4,000 years ago. As time went on the monument fell into neglect and disuse, some of its stones fell over while others were taken away. [ In Photos: A Walk Through Stonehenge]

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There is an interesting connection between the earlier Cursus monuments and the later Stonehenge. Archaeologists found that the longest Cursus monument had two pits, one on the east and one on the west. These pits, in turn, align with Stonehenge's heel stone and a processional avenue.

"Suddenly, you've got a link between [the long Cursus pit] and Stonehenge through two massive pits, which appear to be aligned on the sunrise and sunset on the mid-summer solstice," said University of Birmingham archaeologist Vincent Gaffney, who is leading a project to map Stonehenge and its environs.

Some of the people who built Stonehenge may have lived near the monument at a series of houses excavated at Durrington Walls. Recently, archaeologists discovered evidence that people who lived in these houses feasted on meat and dairy products. The rich diet of the people who may have built Stonehenge provides evidence that they were not slaves or coerced, said a team of archaeologists in an article published in 2015 in the journal Antiquity.

Many theories have been put forward so to why Stonehenge was constructed.

"It's part of a much more complex landscape with processional and ritual activities that go around it," Gaffney told Live Science, noting that people may have traveled considerable distances to come to Stonehenge.

One theory about Stonehenge, released in 2012 by members of the Stonehenge Riverside Project, is that Stonehenge marks the "unification of Britain," a point when people across the island worked together and used a similar style of houses, pottery and other items.

It would explain why they were able to bring bluestones all the way from west Wales and how the labor and resources for the construction were marshaled.

"Stonehenge itself was a massive undertaking, requiring the labor of thousands to move stones from as far away as west Wales, shaping them and erecting them. Just the work itself, requiring everyone literally to pull together, would have been an act of unification," said professor Mike Parker Pearson of the University of Sheffield in a news release.

Additional resources

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Stonehenge: Facts & Theories About Mysterious Monument

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Stonehenge is a massive stone monument located on a chalky plain north of the modern-day city of Salisbury, England. Research shows that the site has continuously evolved over a period of about 10,000 years.

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- Born 100 A.D.
- Greek Mathematician
- Location: Alexandria in Roman province of Egypt
- Founder of Ptolemaic model of solar system; Earth is at center, everything else revolves around Earth
- Epicycles explained the backwards motion of planets

- 80 circular paths to explain motion of the known celestial bodies

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- 1473-1543
- Location: Poland
- Founder of Heliocentric model; Sun is the center, everything revolves around it
- Most accurate model of its time
- Orbits are in circles

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- 190 B.C.-120 B.C.
- Location: Greece
- One of the first to theorize that the Earth orbited around the Sun
- Considered the founder of Trigonometry
- Ranked the stars by brightness

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- 1546-1601
- Location: Europe (Denmark)
- Studied astrology, alchemy and medicine
- Made his observations in his own observatory utilizing his own instruments he made
- Kept detailed records of stars, planets, and other astronomical events including a comet and a supernova
- identified positions of celestial bodies which helped in the creation of the laws of planetary motion

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- 1564-1642
- Location: Italy
- Mathematician and philosopher
- Used new technology of the time; he constructed his own telescope
- Discovered: moons geography, sun spots on sun and Jupiter’s moons
- Published his work supporting Heliocentric model; jailed for opposing the churches common belief

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- 1571-1630
- Location: Germany
- Used Brahe’s work
- Founder of Kepler’s Laws of Planetary Motion
- 1: The orbital paths of the planets are elliptical (not circular), with the Sun at one focus; eccentricity; closer to 0 = circular, closer to 1 = ovular
- 2: An imaginary line connecting the Sun to any planet sweeps out equal area in equal amounts of time
- 3: The square of a planets orbital period is proportional to the cube of it’s semimajor axis

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- Hans Lippershey
-  First patented in 1608
- Location: The Netherlands (Dutch)
- Utilized an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation
- Reflecting Telescope: a mirror where the light will bounce off and is then focused into a smaller area
- Refracting Telescope: uses lenses that focus the light as it travels towards the other end

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- 1643-1727
- Location: England
- Discovered gravity and the law of universal gravitation
- Acceleration due to gravity g=9.81 m/s^2

- Law of inertia: an object in motion will remain in motion unless acted on by an outside force
- Universal gravitational: Every particle attracts every other particle in the universe with a force directly proportional to the product of their masses and inversely proportional to the distance between their centers

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Isaac Newton - who lived from December 25th, 1642, to March 20th, 1727 - was an English scientist, mathematician, and "natural philosopher". In his time, he played a vital role in the Scientific Revolution, helping to advance the fields of physics, astronomy, mathematics and the natural sciences. From this, he established a legacy that would dominate the sciences for the next three centuries.

In fact, the term "Newtonian" came to be used by subsequent generations to describe bodies of knowledge that owed their existence to his theories. And because of his extensive contributions, Sir Isaac Newton is regarded as one of the most influential scholars in the history of science. But what exactly did he discover?

Newton's Three Laws of Motion:

For starters, his magnum opus - Philosophiæ Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"), which was first published in 1687 - laid the foundations for classical mechanics. In it, he formulated his Three Laws of Motion, which were derived from Johann Kepler's Laws of Planetary Motion and his own mathematical description of gravity.

The first law, known as the "law of inertia", states that: "An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force." The second law states that acceleration is produced when a force acts on a mass - ergo, the greater the mass of the object, the greater the force required to accelerate it. The third and final law states that "for every action, there is an equal but opposite reaction".

Universal Gravitation:

He also formulated his law of Universal Gravitation in the Principia, which states that every point mass attracts every single other point mass by a force pointing along the line intersecting both point. According to his calculations, this force is proportional to the product of the two masses and inversely proportional to the square of the distance between them. The formula for this theory can be expressed as:

Newton would go on to use these principles to account for the trajectories of comets, the tides, the precession of the equinoxes, and other astrophysical phenomena. This effectively removed the last doubts about the validity of the heliocentric model of the cosmos which argued that the Sun (not the Earth) was at the center of the planetary system. His work also demonstrated that the motion of objects on Earth and of celestial bodies could be described by the same principles.

Though Newton's inspiration for his theories on gravity are often attributed to the "Apple Incident" - i.e. where he watched an apple fall from a tree - the story is considered apocryphal by modern sources who argue that he came to his conclusions over time. However, Newton himself described the incident, and contemporaries of his defend this assertion.

Shape of the Earth:

Additional contributions include his prediction that the Earth was likely shaped as an "oblate spheroid" - i.e. a sphere that experienced flattening at the poles. This theory would later be vindicated by the measurements of Maupertuis, La Condamine, and others. This in turn helped convince most Continental European scientists of the superiority of Newtonian mechanics over the earlier system of Descartes.

In terms of mathematics, he contributed to the study of power series, generalized the binomial theorem to non-integer exponents, developed Newton's method for approximating the roots of a function, and classified most of the cubic plane curves. He also shares credit with Gottfried Leibniz for the development of calculus.

These discoveries represented a huge leap forward for the fields of math, physics, and astronomy, allowing for calculations that more accurately modeled the behavior of the universe than ever before.

Optics:

In 1666, Newton began contributing to the field of optics, first by observing that color was a property of light by measuring it through a prism. From 1670 to 1672, he lectured at the University of Cambridge on optics and investigated the refraction of light, demonstrating that the multicolored spectrum produced by a prism could be recomposed into white light by a lens and a second prism.

As a result of his research, he came to theorize that color is the result of objects interacting with already-colored light rather than objects generating the color themselves, which is known as Newton's theory of color.

In addition, he concluded that the lens of any refracting telescope would suffer from the dispersion of light into colors (chromatic aberration). As a proof of the concept, he constructed a telescope using a mirror as the objective to bypass that problem. This was the first known functional reflecting telescope in existence, the design of which is now known as a Newtonian telescope.

Other Achievements:

He also formulated an empirical law of cooling, studied the speed of sound, and introduced the notion of a Newtonian fluid. This term is used to describe any fluid where the viscous stresses arising from its flow, at every point, are linearly proportional to the rate of change of its deformation over time.

Beyond his work in mathematics, optics and physics, he also devoted a significant amount of time studying Biblical chronology and alchemy, but most of his work in these areas remained unpublished until long after his death.

So what did Isaac Newton discover? Theories that would dominate the fields of science, astronomy, physics and the natural world for centuries to come. His ideas would go on to influence such luminaries as Joseph-Louis Lagrange and Albert Einstein, the latter of whom is the only scientists believed to have left a comparable legacy.

We have written many interesting articles about Sir Isaac Newton here at Universe Today. Here's Who was Sir Isaac Newton?, What did Isaac Newton Invent?, Who Discovered Gravity?, What is Absolute Space?, What is the Gravitational Constant?

There are other resources on the internet if you want to learn more about Isaac Newton. This UK site has some great info on his discoveries. You can also check out the PBS website.

You can also check out Astronomy Cast. Episode 44 Einstein's Theory of Relativity is particularly interesting.

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What Did Isaac Newton Discover? - Universe Today

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Isaac Newton - who lived from December 25th, 1642, to March 20th, 1727 - was an English scientist, mathematician, and "natural philosopher". In his time, he played a vital role in the Scientific Revolution, helping to advance the fields of physics, astronomy, mathematics and the natural sciences.

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- 1879-1955
- Location: Germany
- Developed theories of special and general relativity
- Special Relativity: relating space and time. The observance of space and time are relative to each individual observer
- General Relativity: theory of gravitation that explains how objects with mass warp space time: massive objects bend space and slow down time

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Do you really understand Einstein’s theory of relativity? - BBC News

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- 1942-2018
- Location: Europe (United Kingdom)
- Predicted the existence of black holes and how they emit Hawking radiation
- Hawking Radiation: electromagnetic radiation given off by a black hole, due to quantum effects, causes it to lose matter. If a black hole loses more matter than it gains, it could shrink and eventually vanish

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Hawking's black hole paradox explained - Fabio Pacucci