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Višnja Šuperba, Croatia

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Trying to estimate the angle, so to be precise we transfered our calculations in the classroom's board by recreating our triangle. φ=41o

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85 cm - our ruler is 100 cm. The ruler is straight. The angle of the photo changes the way it looks, it is straight!

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Το πείραμα του Ερατοσθένη 2018 - Γυμνάσιο Ιερισσού Χαλκιδική, Ελλάδα - Ευγενία Σακελλαριάδη.

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Το πείραμα του Ερατοσθένη 2018 - Γυμνάσιο Ιερισσού Χαλκιδική, Ελλάδα - Ευγενία Σακελλαριάδη.

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Ζήτω! Έχουμε σκιά. Horray we have got a shadow!

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Ierissos Junior High School, Chalkidiki, Greece.

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Ierissos Junior High School, Chalkidiki, Greece.

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Though an English teacher, I conducted the Eratosthenis experiment 2018, for the first time. Really interesting and we got really excited. Next year we will be more experienced! Thank you for the opportunity.
Eugenia Sakellariadis

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vila real, portugal

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20.03.201

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This year the experiment will take place on Wednesday the 21st of March, one day after the spring equinox day (Tuesday, 20 March 2018, 16:15 UTC).
Eratosthenes devised a system of latitude and longitude and a calendar that included leap years. He invented the armillary sphere, a mechanical device used by early astronomers to demonstrate and predict the apparent motions of the stars in the sky. He also compiled a star catalog that included 675 stars. His measurement of the circumference of Earth was highly respected in his day and set the standard for many years thereafter. He may have also measured the distances from Earth to both the Moon and to the Sun, but the historical accounts of both deeds are, unfortunately, rather cryptic. A crater on Earth's Moon is named after Eratosthenes.

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2. How Eratosthenes calculated the Earth's circumference

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How Eratosthenes calculated the Earth's circumference

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The Eratosthenes Experiment is organised with the collaboration of the Hellenic Mathematical Society, the participation of the UNESCO regional bureau for Science and Culture in Europe, Venice (Italy) and is approved by the Department of Education in Greece.

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Vila Real, Portugal
41º 17´ 45´´ N  ; 7º 44´ 46´´  O
Visit Eratosthenes Experiment official website,  http://eratosthenes.ea.gr

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Eratosthenes made a surprisingly accurate measurement of the circumference of the Earth. Details were given in his treatise On the measurement of the Earth which is now lost. However, some details of these calculations appear in works by other authors such as Cleomedes, Theon of Smyrna and Strabo. Eratosthenes compared the noon shadow at midsummer between Syene (now Aswan on the Nile in Egypt) and Alexandria. He assumed that the sun was so far away that its rays were essentially parallel, and then with a knowledge of the distance between Syene and Alexandria, he gave the length of the circumference of the Earth as 250,000 stadia.

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Eratosthenes knew that on the day of the summer solstice in the city of Siena, the Sun at noon is exactly at its zenith, illuminating the bottom of deep wells. Indeed, this city is located on the line of the northern tropic. On this day, Eratosthenes measured the height of the Sun in Alexandria and found that it is a quarter of a circle from the zenith. The distance between these cities was known and amounted to 5000 stages. Consequently, the entire circumference of the globe has a length of 50 times greater - 250,000 stages or 39,600 kilometers. Perhaps the real accuracy of the measurements was somewhat lower and the result was only accidentally so close to reality, but the fact remains - a more accurate value could be obtained only in the XVIII century ...

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ERATOSPHEN
Kirenskiy
(ca.276-194 BC)
Ancient Greek scientist. He was born in Cyrene (North Africa). Educated in Alexandria and Athens. Served as the tutor of the Crown Prince at the court of Ptolemy III Everget, around 225 BC. e. began to run the Alexandria Library. He laid the foundations of mathematical geography, for the first time measured the arc of the meridian. With great accuracy, he determined the inclination of the ecliptic, he compiled a catalog of 675 fixed stars. He laid the foundations of scientific chronology, proposed to introduce an extra day into the calendar every 4 years. Works on mathematics (number theory), astronomy, philology, philosophy, music. Only fragments have survived.

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Georgia
Eratosthenes also calculated the Sun's diameter. According to Macrobious, Eratosthenes made the diameter of the Sun to be about 27 times that of the Earth. The actual figure is approximately 109 times.
During his time at the Library of Alexandria, Eratosthenes devised a calendar using his predictions about the ecliptic of the Earth. He calculated that there are 365 days in a year and that every fourth year there would be 366 days.
He was also very proud of his solution for Doubling the Cube. His motivation was that he wanted to produce catapults. Eratosthenes constructed a mechanical line drawing device to calculate the cube, called the mesolabio. He dedicated his solution to King Ptolemy, presenting a model in bronze with it a letter and an epigram. Archimedes was Eratosthenes' friend and he, too, worked on the war instrument with mathematics. Archimedes dedicated his book The Method to Eratosthenes, knowing his love for learning and mathematics.

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Aspa Theohari  / Crete Greece                                                                                             

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Aspa Theohari  / Crete Greece                                                                                             

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Eratosthenes (c. 276 BCE to c. 195 BCE)  was a Greek scholar and his name in greek means  the "power of love". He was commonly known as the "father of geography," due to the fact that he essentially invented it as a scholarly subject.
Eratosthenes was the first to use the word geography.
He studied under the Stoic Greek philosophers Zeno, Ariston, Lysanias, and the poet-philosopher Callimachus. He was also a gifted philosopher, mathematician,  poet, astronomer and musical theorist.
Eratosthenes was a close friend of the famous Greek mathematician Archimedes. He wrote Geographica based on his calculations of the circumference of the earth. He made the first geographical map. He invented the leap year.
Eratosthenes worked out the method by which we could calculate the circumference of the earth using basic geometry.
Greek scholars knew by then that the earth was indeed a sphere.
He knew the approximate distance between Syene and Alexandria, as measured by caravans. He measured the angle of the shadow in Alexandria on the solstice. By taking the angle of the shadow (7°12') and dividing it into the 360 degrees of a circle (360 divided by 7.2 yields 50), Eratosthenes could then multiply the distance between Alexandria and Syene by 50.
He remarkably determined the circumference to be 25,000 miles, just 100 miles over the actual circumference at the equator (24,901 miles).
The Greek geographer Posidonius insisted that Eratosthenes' circumference was too large. He calculated the circumference on his own and obtained a figure of 18,000 miles--7,000 miles too short. During the middle ages, most scholars accepted Eratosthenes' circumference, though Christopher Columbus used Posidonius' circumference to convince his supporters that he could quickly reach Asia by sailing west from Europe. As we now know, this was a critical error on Columbus' part. Had he used Eratosthenes' figure instead, Columbus would have known he was not yet to Asia when he landed in the New World....

Ηe once said:
"ΟΠΟΙΟΣ ΑΡΙΘΜΟΣ ΔΕΝ ΕΙΝΑΙ ΠΟΛΛΑΠΛΑΣΙΟ ΚΑΝΕΝΟΣ  ΜΙΚΡΟΤΕΡΟΥ ΤΟΥ, ΠΛΗΝ ΤΟΥ 1,  ΕΙΝΑΙ ΠΡΩΤΟΣ."
An efficient method of identifying prime numbers.                                                            The so called "Eratosthenes  Sieve"  below

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 Eratosthenes measured the altitude of the noontime sun at Alexandria at its maximum on Jun 21st. On that date, the Sun is directly overhead at noontime at Syene, in southern Egypt (latitude = 23.5 degrees north).The zenith distance is the angle from the zenith to the point where the Sun was at noon; it is also 90 degrees minus the altitude. At Syene, the zenith distance was 0 degrees; at Alexandria it was about 7 degrees.He knew how far it was from Alexandria to Syene, so he used geometry and the difference in zenith angle to estimate the size of the Earth.

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 Eratosthenes measured the altitude of the noontime sun at Alexandria at its maximum on Jun 21st. On that date, the Sun is directly overhead at noontime at Syene, in southern Egypt (latitude = 23.5 degrees north).The zenith distance is the angle from the zenith to the point where the Sun was at noon; it is also 90 degrees minus the altitude. At Syene, the zenith distance was 0 degrees; at Alexandria it was about 7 degrees.He knew how far it was from Alexandria to Syene, so he used geometry and the difference in zenith angle to estimate the size of the Earth.

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Excerpt from the IBM film "Mathematics Peepshow".

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Eratosthenes was born in the country we now call Lybia, but in those days was called Cyrene. Eratosthenes will always be remembered for the calculation of the Earth's circumference circa 240 BC, using trigonometry and knowledge of the angle of elevation of the Sun at noon in Alexandria and Syene (now Aswan, Egypt). The calculation is based on the assumption that the Earth is spherical and that the Sun is so far away that its rays can be taken as parallel.
Eratosthenes' experiment was one of the most important experiments in antiquity and his estimate of the earth’s size was accepted for hundreds of years afterwards. It was, in fact, the most accurate estimate until Man was able to go to Space.

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https://aidafizika.wordpress.com/2016/08/01/%D0%B5%D0%BA%D1%81%D0%BF%D0%B5%D1%80%D0%B8%D0%BC%D0%B5%D0%BD%D1%82%D0%B8/