Eratosthenes

  • Eratosthenes, born in Cyrene, calculated the size of the Earth in 276 BC
  • He used astronomical observations and the armillary sphere for his scientific research.
  • He estimated the distance between the Earth and the Sun with remarkable accuracy for his time.
  • His work influenced future scientists such as Ptolemy and Christopher Columbus.

Eratosthenes

Throughout history, there have been a few people who have greatly advanced knowledge about our planet. One of these men was Eratosthenes. He was born in Cyrene in the year 276 BC. It was in being able to calculate the size of the Earth thanks to his studies on astronomy and his great deductive capacity. Despite the very little technology of that time, people like Eratosthenes made giant strides in understanding our planet.

In this article we are going to tell you the biography and feats of Eratosthenes.

His principles

Armillary sphere of Eratosthenes

We must bear in mind that at this time, there was virtually no observational technology, so astronomy was in its infancy. Therefore, Eratosthenes's recognition is quite high. Initially, he studied in Alexandria and Athens. He became a disciple of Ariston of Chios, Callimachus, and Lysanias of Cyrene. He was also a great friend of the well-known Archimedes.

It was nicknamed as Beta and Pentatlos. These nicknames meant a reference to a type of athlete who is capable of being part of several specialties and who, because of this, is not capable of being excellent in any of them and is always second. This makes it quite a harsh nickname for him. Despite that nickname, he was able to use its bases for later very interesting scientific findings.

He worked practically all his life in the library of Alexandria. According to some people, he lost his sight at the age of 80 and allowed himself to starve. He is the creator of the armillary sphere, an instrument of astronomical observation that was still used in the seventeenth century. This may reveal how capable you were at the time you lived. It was thanks to the armillary sphere that he was able to know the obliquity of the ecliptic.

He was able to calculate the interval between the tropics and these figures were later used by Ptolemy in some of his studies such as the geocentric theory. He was also observing eclipses and was able to calculate that the distance from the Earth to the Sun was 804.000.000 furlongs. If the stadium measured 185 meters, this gave 148.752.000 kilometers, a figure very close to the astronomical unit.

importance of historical cartography
Related article:
Historical cartography

Observation research

Distances from Eratosthenes

Between his investigations, he spent a long time making observations and providing distance calculations. Another piece of information he was able to provide was that the distance from the Earth to the Moon was 780.000 furlongs. This is currently known to be almost three times higher. However, taking into account the technology that existed at that time, it cannot be said that it was a scientific advance.

Thanks to the observations he made with the armillary sphere, he was able to calculate the diameter of the Sun. He said it was 27 times that of the Earth, although today it is known that it is 109 times more.

During his years of learning, he was studying prime numbers. In order to calculate the size of the Earth, he had to invent a trigonometry model where he applied the notions of latitude and longitude. These experiments and calculations had been used before, just not in such a close way.

Since he worked in the library, he was able to read a papyrus that said that June 21 was the Summer Solstice. This meant that, at noon, the Sun would be closer to zenith than any other day of the year. This could be easily demonstrated by driving a stick vertically into the ground and seeing that it did not cast any shadow. Of course, this only happened over Syene, Egypt (which is where the terrestrial equator is located and where the sun's rays arrive completely perpendicular on the day of the summer solstice).

If this shadow experiment was done in Alexandria (located 800 km north of Syene) you could see how the stick cast a very short shadow. This meant that in that city, the noon sun was about 7 degrees south of the zenith.

Zealand located on the map
Related article:
Zealandia: A new continent hidden under the Pacific Ocean

Calculation of distances from Eratosthenes

Eratosthenes calculations and discoveries

The distances between the two cities could be taken from the caravans that traded between these cities. It is possible that he could have these data from among the thousands of papyri in the library of Alexandria. There are some rumors that say that he had to use a regiment of soldiers to count the steps they took between the two cities and that this is how he calculated the distances.

If we see that Eratosthenes used the Egyptian stadium, which is about 52,4 cm, this would make the earth's diameter 39.614,4 kilometers. This makes it possible to calculate it with an error of less than 1%. These figures were later somewhat modified by Posidonius 150 years later. The figure came out somewhat lower and is the one used by Ptolemy and on which Christopher Columbus relied to be able to demonstrate the usefulness and veracity of his travels.

Another of Eratosthenes' discoveries was to calculate the distance from the Earth to the Sun and from the Earth to the Moon. Ptolemy is the one who says that Eratosthenes was able to measure the inclination of the Earth's axis quite accurately. He was able to collect a fairly reliable and exact data of 23º51'15 ”.

Other contributions

Alexandria

He left all the results he discovered in his studies in his book entitled "On the Measurements of the Earth." This book is now lost. Other authors, such as Cleomedes, Theon of Smyrna and Strabo reflected in their works the details of these calculations. It is thanks to these authors for the fact that we can have the necessary information about Eratosthenes and its data.

With all that we have seen, it cannot be argued about the great contribution that Eratosthenes made to science. In addition to these, he also carried out many other works including the design of a leap calendar and a catalog with 675 stars and their nomenclature. He was also able to draw the route of the Nile to Khartoum quite accurately, including some tributaries. In short, he was not at all worthy of the nickname Beta, much less so because of its meaning.

I hope this information helps you to know more about Eratosthenes.


Leave a Comment

Your email address will not be published. Required fields are marked with *

*

*

  1. Responsible for the data: Miguel Ángel Gatón
  2. Purpose of the data: Control SPAM, comment management.
  3. Legitimation: Your consent
  4. Communication of the data: The data will not be communicated to third parties except by legal obligation.
  5. Data storage: Database hosted by Occentus Networks (EU)
  6. Rights: At any time you can limit, recover and delete your information.