4 amazing astronomical discoveries from ancient Greece

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The ancients made some amazing discoveries without modern technology. For example, the size of the moon.

The blue semicircle-the earth-and the smaller yellow semicircle-the moon-on a black background.

The earth and moon seen by the Galileo spacecraft. Picture from NASA/Dialogue.

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Illustration:Galileo spacecraft in space

Source:Baidu Encyclopedia

Herodotus (484 BC to 425 BC)’s”History” provides a window into the world, as the ancient Greeks knew it in the middle of the fifth century BC. What is as interesting as what they don’t know is what they know. This laid the foundation for them, and in the next few centuries they made remarkable progress in understanding—things that can be observed only with their eyes.

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Herodot claims that Africa is almost completely surrounded by the ocean. How did he know? He tells the story of Phoenician sailors who were sent to the African continent by King Nico II of Egypt (about 600 BC) to sail clockwise from the Red Sea. This story, if true, records the earliest known circle of Africa and also contains interesting insights into astronomical knowledge of the ancient world.

This voyage took several years. The sailors circled the southern tip of Africa, following the route of the westerly wind, observing the sun on the northern horizon on their right. This observation was meaningless at the time, because they did not know that the earth was spherical and they were in the southern hemisphere.

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One. Planets revolve around the sun

After centuries, great progress has been made. Aristarchius of Samos (310 BC to 230 BC) believed that the sun was the”central fire” of the universe, and he arranged all the planets known at the time in the correct order of their surrounding distances. This is the earliest known heliocentric theory of the solar system.

Unfortunately, the original text of his argument has been forgotten by history, so we are not sure how he solved this problem. Aristarchius knew that the sun was much larger than the earth or the moon, and he might speculate that the sun should be in the center of the solar system.

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Illustration:Planets circling the sun

Source:Baidu Encyclopedia

However, this is a jaw-dropping discovery, especially since it was not discovered by Nicholas Copernicus until the 16th century, and Copernicus even admitted it during the development of his work The view of Aristarchius.

Two. The size of the moon

Aristachus’s book is about the size and distance between the sun and the moon. In this remarkable paper, Aristarchius described the earliest known tentative calculations of the relative size and distance of the sun and moon.

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People have long noticed that the sun and moon are in the sky The external dimensions are the same, and the sun is farther away. They realized this from a solar eclipse, which is caused by the moon passing in front of the sun at a certain distance from the earth.

In addition, when the moon is in the first or third quarter, Aristarchius believes that the sun, the earth and the moon will form a right triangle.

Since Pythagoras has determined how the lengths of the triangle sides are connected centuries ago, Aristachus used this triangle to estimate the distance from the sun to the moon. 18 to 20 times of that. He also estimated that the size of the moon is about one-third the size of the earth, which is based on careful timing of the lunar eclipse.

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Illustration:the moon, the earth, and the sun keep one fit The distance of

Source:Baidu Encyclopedia

Three circles drawn in red on parchment, connected with diagonal lines, and annotated in Greek.

A diagram copied by Aristarchius in the 10th century, showing some of the geometry he used in his calculations.

Although his estimated distance from the sun is too low (the actual ratio is 390), considering the lack of available telescope accuracy at the time, the value of the ratio of the size of the earth to the moon Surprisingly accurate (the diameter of the moon is 0.27 times that of the earth).

Today, we have accurately known the size and distance of the moon through various means such as precise telescopes, radar observations, and laser reflectors left by the Apollo astronauts on the surface of the moon.

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Three. Circumference of the Earth

Elatosenes (276-195 BC) was the chief librarian of the Great Library of Alexandria, and an enthusiastic experimenter. Among his many achievements, one is the earliest known calculation of the circumference of the earth. Although Pythagoras did not calculate the size of the earth, it is generally considered to be the earliest supporter of the spherical earth. Eratosnis’s famous and simple method is to measure different shadow lengths. At noon on the summer solstice, the poles are projected vertically to the ground at different latitudes.

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Illustration:Sundial using shadow to measure time

Source:Baidu Encyclopedia

As Aristachus showed before, because the sun is far enough away from the earth, no matter where the light reaches, they are actually parallel. So the difference in shadow shows the degree of curvature of the earth’s surface. Eratochenes used this to estimate the circumference of the earth to be approximately 25,000 miles (40,000 kilometers). According to modern geodesy (the science of the shape of the earth), the accuracy of this value is within a few percent of the actual value.

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Illustration:Parallel sunlight

Source:Baidu Encyclopedia

Later, another scientist Bosidoni (from 135 BC to 51 BC) used a slightly different method and got almost the same answer. Posidones has lived on Rhode Island for most of his life, where he observed the bright Canopus star very close to the horizon. However, when he was in Alexandria, Egypt, he noticed that Kanops would rise to about 7.5 degrees above the horizon.

Considering that 7.5 degrees is 1/48 of a circle, he multiplies the distance from Rhodes to Alexandria by 48, and the value is also approximately 25,000 miles (40,000 kilometers).

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four. The first astronomical calculator

The oldest mechanical calculator in the world is the Antixila machine. This amazing device was discovered in 1900 on an ancient shipwreck near Antikythera, Greece.

With the passage of time, this device is now fragmented, but if it is intact, it will be a box with dozens of finely machined bronze gears. When manually rotated with the handle, the gear rotates the dial on the outside to display the phase of the moon, the time of the lunar eclipse, and the positions of five known planets (Mercury, Venus, Mars, Jupiter and Saturn) at different times of the year. This even explains their retrograde motion—the illusory change of planets moving in the sky.

We don’t know who built it, but it can be traced back to the 3rd to 1st century BC, and may even be the work of Archimedes. For thousands of years, with the maturity of the Antikythera mechanism, gear transmission technology has never appeared again.

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Sadly, most of these works are Forgotten by history, our scientific awakening has been delayed for thousands of years. As a tool for introducing scientific measurement, Eratosenes’ technology is relatively easy to implement and does not require special equipment, allowing those who are just beginning to be interested in science to understand through hands-on, experimentation, and finally following the footsteps of the first scientists. science.

If this ancient science continues to develop, people can only speculate about how far our civilization may develop now.

Gareth Dorrian, a postdoctoral researcher in space science at the University of Birmingham and Ian Whittaker, a lecturer in physics at Nottingham Trent University

One sentence:Four astronomical discoveries in ancient Greece.

Author:EarthSky Voices-Gareth Dorrian

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