Question

1. who first suggested that the earth is round? 2. what method did eratosthenes use to calculate the earth’s circumference? 3. during which historical period did early scientific calculations about astronomy begin?

Explanation:

Question 1

The idea of the Earth being round was first proposed by ancient Greek philosophers. Pythagoras (in the 6th century BC) is often credited with being among the first to suggest the Earth is spherical, based on philosophical and mathematical reasoning about symmetry and the nature of the universe. Later, other Greek scholars like Parmenides and Aristotle provided further support (Aristotle, for example, used observations like the shape of the Earth's shadow during lunar eclipses).

Eratosthenes calculated the Earth’s circumference by using the angle of the Sun’s rays at two different locations (Alexandria and Syene, modern - day Aswan) on the summer solstice. He knew the distance between the two cities. At Syene, the Sun was directly overhead (so a well had no shadow), while at Alexandria, there was a small shadow, creating an angle. He used the concept of similar triangles and the proportion of the angle (about 7.2 degrees, or 1/50 of a full circle) to the full 360 - degree circle, and then multiplied the distance between the cities by 50 to get the circumference.

Early scientific calculations about astronomy began in the ancient period, particularly in ancient civilizations like Mesopotamia (Babylonian astronomy, around the 2nd millennium BC), ancient Egypt, and especially ancient Greece (from the 6th century BC onwards). The ancient Greek period saw significant developments with philosophers and astronomers like Pythagoras, Thales, and later Hipparchus and Ptolemy. Also, in ancient India and China, there were early astronomical observations and calculations. The "ancient" or "classical antiquity" period (encompassing ancient Greek, Mesopotamian, Egyptian, etc., civilizations) is when systematic early astronomical calculations started.

Answer:

Pythagoras (or among the ancient Greek philosophers; more precisely, Pythagoras in the 6th century BC is often cited as one of the first to propose the Earth is round, with later support from others like Aristotle).

Question 2