Alexander the Great, king of Macedonia in northern Greece, conquered the Persian Empire (present-day Iran) in 330 BC. Before that, the Persian Empire had conquered from Gandhara (Afghanistan) to the south-western border of the Indus Valley to the Hydaspis River.

When Alexander the Great crossed the Hindkush Mountains from Gandhara and tried to cross the Hydaspis River in 326 BC, he had to fight the army of the then king of the Indus Valley, Poros. That war is called 'Battle of Hydaspis'. Hydaspis in Greek means river Jhelum.

Brief information about this is mentioned in 'The Imperial Gazetteer of India', Volume 19, published in 1908. After the war, Alexander the Great placed soldiers, administrators and non-military Macedonians in the territories he conquered. They established Greek art, language, architecture, and governance there. Thus the Griselli culture called Hellenistic culture came into vogue in South Asia.

The literary tradition in Greece began in 1200 BC. Thales of Miletus, Solon of Athens, Chilon of Sparta, Pythacus of Mytilene, Cleobulus of Lindos and Periander of Corinth, born in the seventh and sixth centuries BC, are the 'Seven Wise Men' or 'Seven Sages' of Greece.

'Sage' means Rishi and Saptarishi called 'Seven Sages'. The 'Seven Sages' are considered to be the heritage of the ancient Greek civilization. Atri, Bhrigu, Angiras, Vashishtha, Kashyapa, Gautama and Jagadgni are Saptarishis mentioned in Rigveda and mythology. It is not certain when this legendary sage was born. This article will discuss the study of the earth and solar system by Greek and Hindu astrologers. 

Earth and the Universe 

Thales of Miletus is considered the leading sage among the seven sages in the ancient history of Greece. Thales, born in 625 BC, believed that the earth was flat and floating in the sea. Pythagoras, born in Greece in 570 BC, was the first to postulate that the earth is round. It was understood that the universe is round, since the earth is a part of the universe, the earth must also be round. Similarly, he argued that the earth must be round because the shadow of the earth appears round on the moon. 

The weakness of Pythagoras is that he believed in the geocentric model that the earth is at the center and the sun, moon and other planets revolve around it. The African country of Egypt was under Roman rule in the 2nd century AD. The intellectual figure in Egypt at that time was Claudius Ptolemy. He refined the geocentric model by adding much information about the planets and the Earth, including planetary orbits. From that, it was established that the earth is at the center and the sun, moon and planets revolve around the earth. 

Nicholas Copernicus of Poland was a great mathematician and astronomer of the 15th century. He was against the geocentric model. He said that the earth is not at the center of the sun, moon and planets. Copernicus proposed the heliocentric model, with the sun at the center of the universe, saying that the earth rotates daily in its orbit. Even stars move in different orbits.

However, that idea was not Copernicus's alone. Even before that, such a belief was being discussed. He clarified those beliefs on the basis of mathematics. He was timid. They did not advance that belief because of fear. Copernicus' concept was clearly confirmed by the contributions of Johannes Kepler, Galileo Galilei and Isaac Newton.

Kepler's laws of planetary motion, Galileo's telescopic observations and Newton's laws of gravitation were derived from the same Copernicus. Copernicus' heliocentric model eventually helped lay the foundation for the Scientific Revolution in the 16th and 17th centuries. This has greatly helped people to understand the universe. 

The heliocentric model became popular because of Galileo's telescope. The Roman Catholic Church did not agree with what Galileo saw and discussed. It was different from the Bible that the earth, moon and planets revolve around the sun. According to the geocentric model, the positions of the sun, moon, and earth were written in the Bible at that time. He was warned by the Church in 1616. 

The Catholic Church declared heliocentric talk a heretic. Despite the ban on advocating heliocentricity, Galileo wrote two books on heliocentricity. He is then forced to reject the heliocentric belief, accusing Bo in Rome of spreading religious intolerance. Not only that, he spends the rest of his life under house arrest. 

Euclid and Eratosthenes

In Greece there was a mathematician named Euclid in the third century BC. He is also known as the father of geometry within mathematics. His most famous work on mathematics is 'The Elements'. It is said that Euclid's 'The Elements' is the most translated material in the Western world apart from the Bible. Although he wrote a total of 13 books by collecting works written on mathematics before him, his special interest was in geometry. 

He presented information about radius, circumference etc. of a circular object. Studied related to angle ie angle and its circle. Similarly, angles and the area occupied by spherical objects were also studied by him. Euclid proposed that if two parallel lines were crossed by a third line, the alternate interior  proved that

angles are equal (Mary Gow, 2010: Measuring the Earth: Erasthenes and his Celestial Geometry, p. 53). This fact is taught in school geometry today. 

Eratosthenes, born in Greece in 276 BC, was a scientist, writer, astronomer and poet. During his time, the African country of Egypt was under the Ptolemaic dynasty of Greece. Eratosthenes lived in Egypt. Eratosthenes was the head of the library of Alexandria, Egypt. His Alexandria was a center of learning for the world. 

Until the time of Eratosthenes, the extent of the earth was not known. At that time, the New World (North and South America) including Australia, Antarctica was not known. In this case, Eratosthenes measured the circumference of the earth using ordinary instruments. A

was then measured in length stade units. One stade is considered equal to 157.7 meters. He calculated the total circumference of the earth to be 2,52,000 stades or 39,740 km. The actual circumference of the earth is about 40,000 km. Eratosthenes deduced only 260 km less than the Earth's circumference. Even today, we do not know how much the circumference of the earth is, and even if we do, we do not know how to calculate it. 

Method of Measurement

Durane W. Roller's 2010 book titled 'Eratosthenes Geography' contains an illustrated account of how Eratosthenes determined the circumference of the Earth. Eratosthenes calculated the circumference of the earth using an experiment in Egypt. He used the arc measurement method, assuming the earth to be round, to measure the circumference. From this method, the radius of the earth was calculated. 

He chose a place called Alexandria and Sine in Egypt to calculate the radius of the earth. The two places are about 800 km away from each other. He was signed in June. He found that on June 21 at noon, the sun would be directly overhead and no shadow would be visible. For that he buried a straight stick in the ground and looked. As it happened, the shadow of the rod was not seen. 

He had the staff buried in Alexandria at noon on June 21, but the shadow of the staff was seen there. The shadow made an angle of 7.2 degrees with the rod. This means that Eratosthenes believed that these two cities formed an angle of 7.2 degrees to each other. 

In order to calculate the circumference of the earth, he used the data obtained by dividing the circumference of the earth by 360 degrees by dividing the distance between two points by the angle made by the sun's rays. This makes 800 km divided by 7.2 degrees equal to the circumference of the earth divided by 360 degrees. According to the rules of arithmetic, the degrees on the left and right sides of equal two intersect each other. The next step to the left is Earth's circumference × 7.2. 800 km × 360 to the right of Equivalent Two. Calculating this, the circumference of the earth is about 40,000 km. comes out

Surya Siddhanta

It is said that in ancient India, our sages discovered a method to measure the motion of the sun, moon, planets and constellations. Based on that, the method of extracting time and date has been made and such method is written in our ancient books. Western astrologers came to India to learn such a method. They copied the knowledge acquired by our sages. Translated into English and spread around the world. The book 'Surya  written by Hindus about Earth, Sun, Moon and planets. The principle is ''.

American scholar Reverend Ebenezer Burgess came to South Asia in the 19th century. He studied Indian history and culture. Translated ancient Sanskrit texts into English. In this process he translated 'Surya Sidghanta'.

That translation was published in 'The Journal of the American Oriental Society' in 1860. Due to the time, thought and patient labor that he and his colleagues devoted to the translation of 'Surya Sidghanta', Hindu astronomy became known to the world. The book was reprinted by Calcutta University in 1935. Fanindra Lal Ganguly of the Department of Mathematics under the said university supervised this work. In the

book, the original text is translated point by point into English. Then there is the explanation of those points. However, most of the writings sound like Ramayana, Mahabharata or Puranic style narratives. Some things are not according to science. Points are connected to God. He does not agree with the chronology of human development, civilization language, script development etc. For example, it is said in chapter one - 'The sun theory was revealed 21,64,960 years ago', while at that time human ancestors walked on 4 legs in Africa. 

In South Asia, the language and script was in vogue in the Indus civilization about 5-6 thousand years ago. The Indus civilization merged about 4,000 years ago. The wood and clay scripts found in the excavations there have not yet been deciphered. 'Surya Sidghanta' was written in Sanskrit language and Brahmi-derived script. Therefore, it is wrong to write that 'Surya Sidghanta' came 21 lakh 64 thousand years ago. In the book

, the circumference of the earth is discussed by different authors. Yojana units are written in the length scale. A scheme is written which may be 40 or 30 li. However, in religious books it is written that 1 Yojana is 16 li. A li means 500 meters in length measurement. So 1 Yojana is equal to 8 km. 

'Surya Sidghanta' mentions the role of books written by various astronomers in the 5th to 12th centuries AD (AD 499, AD 505, AD 550, AD 628, AD 748, AD 932, AD 1028 and AD 1150). In the book, the circumference of the earth is calculated as 3,0936.75 Yojanas, 4,967 Yojanas, 5,059.556 Yojanas. From this it is clear that the authors of 'Surya Sidghanta' calculated the circumference of the earth from 31,494 km to 40,476 km. Only the latter perimeter is closer to reality.