Eratosthenes Festivity 21 June

Prepared by Reda Kandil Eratosthenes Edited by Ingy Hafez Festivity Designed by 21 June Maha Sherin Supervised by tosthen Maissa Azab ra es E For additional information, please contact: Planetarium Science Center Tel.: +(203) 4839999; Ext. 2350–2351 2 Fax: +(203) 4820464 1 e [email protected] Jun www.bibalex.org/psc Eratosthenes Festivity 21 June Contents Once Upon a Time... Play it Yourself Who am I? Glossary What Did I Do? References How Big is the Earth? Test Yourself 1 2 Who am I? Profile Name: Eratosthenes Nationality: Lybian Once Upon a Time... Birth: 276 BCE, Cyrene (Libyan Arab Jamahiriya) Education: Athens and Alexandria Profession: Scientist and third Librarian of the The Greek scholars elaborated on the observations made by the Ancient Library of Alexandria. ancient Egyptians. This led them to the concepts of demon- Death: 194 BCE stration and mathematical modeling, which are the fundamen- tals of modern science. My name is Eratosthenes. I was born in Cyrene; currently the Considerable progress was made in the field of anatomical medi- Libyan Arab Jamahiriya. Along with Alexandria and Athens, cine thanks to the use of human dissection; a practice previously Cyrene was one of the most prominent cultural cities of the banned for religious reasons and performed for the first time by Mediterranean. I studied in Athens and then moved to Alexandrian doctors. Alexandria where I lived for many years. From the third century BCE to the fifth century CE, scientists I lived at a time of eminent Greek scholars, including my good broadened their scope of investigation. The conquests of Alexander friend Archimedes(1), who was one of the greatest mathematicians the Great provided more detailed knowledge of the world; in history. I earned the nickname Beta(2), the second letter in geography became more precise, and exploration became more the Greek alphabet, from some of my contemporaries who scientific. Moreover, scholars received substantial backing, claimed that I was second best among my peers in everything. particularly financial, from Hellenistic kings, including the I was interested in and practiced numerous fields of science Ptolemies in Alexandria and the Attalids in Pergamon. including astronomy, geography, literature, poetry, philosophy, and mathematics. In 236 BCE, I was appointed Librarian of the Library of Alexandria by Ptolemy III Euergetes I(3), becoming the third Librarian of this illustrious edifice. 1 2 Who am I? Profile Name: Eratosthenes Nationality: Lybian Once Upon a Time... Birth: 276 BCE, Cyrene (Libyan Arab Jamahiriya) Education: Athens and Alexandria Profession: Scientist and third Librarian of the The Greek scholars elaborated on the observations made by the Ancient Library of Alexandria. ancient Egyptians. This led them to the concepts of demon- Death: 194 BCE stration and mathematical modeling, which are the fundamen- tals of modern science. My name is Eratosthenes. I was born in Cyrene; currently the Considerable progress was made in the field of anatomical medi- Libyan Arab Jamahiriya. Along with Alexandria and Athens, cine thanks to the use of human dissection; a practice previously Cyrene was one of the most prominent cultural cities of the banned for religious reasons and performed for the first time by Mediterranean. I studied in Athens and then moved to Alexandrian doctors. Alexandria where I lived for many years. From the third century BCE to the fifth century CE, scientists I lived at a time of eminent Greek scholars, including my good broadened their scope of investigation. The conquests of Alexander friend Archimedes(1), who was one of the greatest mathematicians the Great provided more detailed knowledge of the world; in history. I earned the nickname Beta(2), the second letter in geography became more precise, and exploration became more the Greek alphabet, from some of my contemporaries who scientific. Moreover, scholars received substantial backing, claimed that I was second best among my peers in everything. particularly financial, from Hellenistic kings, including the I was interested in and practiced numerous fields of science Ptolemies in Alexandria and the Attalids in Pergamon. including astronomy, geography, literature, poetry, philosophy, and mathematics. In 236 BCE, I was appointed Librarian of the Library of Alexandria by Ptolemy III Euergetes I(3), becoming the third Librarian of this illustrious edifice. 3 4 How Big is the What Did I Do? Earth? Can you imagine how easy it is to measure the circumference of the Earth? I wrote distinctive works of mathematics, and set some I measured the circumference of the Earth applying a very significant geometric and arithmetic definitions. I simple method that every one of you can easily use. also wrote the first treaty on mathematical I had heard that if you looked into one of the wells in the city geography, including a map of the world. I of Syene (Aswan) at noon, on a midsummer's day, you could see was the one who invented the word “Geography”, the Sun reflected in the water at the bottom and that there was which is derived form the Latin word no shadow. “Geographikos” meaning “Science of Map Drawing”. As the water surface in the well is Moreover, I prepared a map of the Nile valley horizontal, I realized this must Sun light southward to the latitude of the modern Khartoum. mean the Sun was exactly overhead. I also reported that heavy rains hadbeen observed to fall in the upper I deduced that the sun rays were reaches of the river and that these were sufficient to account for the perpendicular; thus, reaching the Well flooding. bottom of wells and the shadow of objects was centered around them, Fig.1 Furthermore, I described “Eudaimon Arabia”; now known as making it seem as if they had no Yemen; as inhabited by four major peoples. Based on my shadow at all (Fig.1). categories, contemporary scholars began to speak of Minaeans, Sabaeans, Qatabanians, and Hadramites. Sun light Other than that, I calculated the ecliptic orbit, as well as the On the other hand, in Alexandria, Ground level distance between the Earth and the Moon, and the Earth and the sun rays were not perpendicular and the same objects had short the Sun. Shadow of the side of the well shadows (Fig.2). However, my most remembered feat is that I measured the Fig.2 circumference of the Earth with outstanding precision through the latitude difference between the ancient city of Syene (Fig.2) Sunlight shining down a well in Alexandria at noon, on the (Aswan) and Alexandria, in Egypt. same day as the observation shown in Fig.1; the Sun is not directly overhead. The ray bar at the bottom left shows the shadow cast by the Unfortunately, none of my works survived; however, many side of the well. extracts have been quoted by my successors. 3 4 How Big is the What Did I Do? Earth? Can you imagine how easy it is to measure the circumference of the Earth? I wrote distinctive works of mathematics, and set some I measured the circumference of the Earth applying a very significant geometric and arithmetic definitions. I simple method that every one of you can easily use. also wrote the first treaty on mathematical I had heard that if you looked into one of the wells in the city geography, including a map of the world. I of Syene (Aswan) at noon, on a midsummer's day, you could see was the one who invented the word “Geography”, the Sun reflected in the water at the bottom and that there was which is derived form the Latin word no shadow. “Geographikos” meaning “Science of Map Drawing”. As the water surface in the well is Moreover, I prepared a map of the Nile valley horizontal, I realized this must Sun light southward to the latitude of the modern Khartoum. mean the Sun was exactly overhead. I also reported that heavy rains hadbeen observed to fall in the upper I deduced that the sun rays were reaches of the river and that these were sufficient to account for the perpendicular; thus, reaching the Well flooding. bottom of wells and the shadow of objects was centered around them, Fig.1 Furthermore, I described “Eudaimon Arabia”; now known as making it seem as if they had no Yemen; as inhabited by four major peoples. Based on my shadow at all (Fig.1). categories, contemporary scholars began to speak of Minaeans, Sabaeans, Qatabanians, and Hadramites. Sun light Other than that, I calculated the ecliptic orbit, as well as the On the other hand, in Alexandria, Ground level distance between the Earth and the Moon, and the Earth and the sun rays were not perpendicular and the same objects had short the Sun. Shadow of the side of the well shadows (Fig.2). However, my most remembered feat is that I measured the Fig.2 circumference of the Earth with outstanding precision through the latitude difference between the ancient city of Syene (Fig.2) Sunlight shining down a well in Alexandria at noon, on the (Aswan) and Alexandria, in Egypt. same day as the observation shown in Fig.1; the Sun is not directly overhead. The ray bar at the bottom left shows the shadow cast by the Unfortunately, none of my works survived; however, many side of the well. extracts have been quoted by my successors. 5 6 Thus, the conclusion that the ratio of this angle In 205 BCE, I proposed a rather simple and precise 7.2° to the 360° of the circle is the same ratio of the method of measuring the circumference of the distance between Alexandria and Syene (800 km) Earth applying my observations of shadows. to the circumference of the circle (the Earth).

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