Astronomical Discoveries

Some astronomical discoveries from ancient Greece

The Histories by Herodotus (484BC to 425BC) offers an unforgettable loop into the world as it was known to the ancient Greeks in the mid-fifth century BC.The Greeks were always ahead in the field of education, science and technology.

The greeks didn't stepped back in the field of astronomy also. 

Here are the few great Astronomical observations by the ancient Greeks that were proved right and amazed the world by their discoveries and observations. All these observations were first taken as mare jokes and flukes but later on they proved to be absolutely true and layer on develped to the facts we know.

 The planets Orbit the Sun

About a few centuries later, there had been a lot of progress. Aristarchus of Samos (310 B.C. to 230 B.C.) argued that the sun was like the “central fire” for the cosmos and placed all of the then known planets in their correct order along with the  correct distance around the sun. This is the earliest known heliocentric theory of the solar system.

Unfortunately, the original text in which he made the argument has been lost in history, so it cannot be know for certain how he worked it out. Aristarchus knew the sun was much bigger than the Earth as well as the moon, and he may have supposed that it should therefore have the central position in the solar system.

Nevertheless it ws a jaw-dropping finding, especially when it is considered that it wasn’t rediscovered until the 16th century, by Nicolaus Copernicus, who even acknowledged Aristarchus during the development of his own work.

 

The size of the Moon

One of Aristarchus’ books that did survive was about the sizes and distances of the sun and moon. In this remarkable treatise, Aristarchus put forward the earliest known attempt of calculations of the relative sizes and distances to the sun and moon.

It had long been observed that the sun and moon appeared to be of the same apparent size in the sky, which is clearified by the fact that the sun was further away. They realized this from solar eclipses, caused by the moon passing in front of the sun at a certain distance from Earth.Also, for an the instant when the moon is at first or third quarter, Aristarchus reasoned that the sun, Earth, and moon would form a right-angled triangle.

Pythagoras had already determined how the lengths of a triangle’s sides were related a couple of centuries earlier, Aristarchus used the triangle to idealise the distance to the sun was between 18 and 20 times the distance to the moon. He also estimated that the size of the moon was approximately one-third that of Earth, based on careful observation on the timing of lunar eclipses.

While his estimated distance to the sun was much low (the actual ratio is 390), on account of the lack of telescopic precision available at that time, and the value for the ratio of the size of the Earth to the moon is surprisingly accurate (the moon has a diameter 0.27 times that of Earth).

Today, we know the size and distance to the moon accurately by a variety of means, including precise telescopes, radar observations and laser reflectors left on the surface by Apollo astronauts. But these observations by Aristarchus at that time were surprisingly amazind and gazing and even these days they are valid to some extent.

 

The Earth's Circumference

Eratosthenes (276BC to 195 B.C.) was the chief librarian at the Great Library of Alexandria and a keen experimentalist. Among his many great achievements ,he also got the credit of the earliest known calculation of the circumference of the Earth. Pythagoras is generally regarded as the earliest proponent to propose the fact of a spherical Earth, although didn't put anything about its size. Eratosthenes’s famous and yet simple method had relied on measuring the different lengths of shadows cast by poles stuck vertically into the ground, at midday on the summer solstice, at different latitudes.

The sun is enough far away that, wherever its rays arrive at Earth, they are considerably parallel, as had previously been shown by Aristarchus. So the difference in the shadows demonstrated how much the Earth’s surface curved. Eratosthenes used this to estimate the Earth’s circumference to a great approximity of 25,000 miles (40,000 km). This is within a couple of percent of the actual value, as established by modern Geodesy (the science of the Earth’s shape).

Later on , another scientist called Posidonius (135 B.C. to 51 B.C.) used a slightly different method and arrived at almost exactly the same answer. Posidonius lived on the island of Rhodes for much of his life. There he observed the bright star Canopus would lie very close to the horizon. However, when in Alexandria, in Egypt, he noted Canopus would ascend to some 7.5 degrees above the horizon.

Given that 7.5 degrees is 1/48th of a circle, he multiplied the distance from Rhodes to Alexandria by 48, and arrived at a value also of approximately 25,000 miles (40,000 km).Which also supports Aristarchus experiment and observations.

The first Astronomical Calculator

The world’s oldest surviving mechanical calculator is the Antikythera Mechanism. The amazing device was discovered in an ancient shipwreck of the Greek island of Antikythera in 1900.

The device had now been fragmented by the passage of time, but when intact it would have appeared to be a box housing dozens of finely machined bronze gear wheels in it. When manually rotated by a handle, the gears spun dials on the exterior showing the phases of the moon, the timing of lunar eclipses, and the positions of the five planets (Mercury, Venus, Mars, Jupiter, and Saturn) known at that time at different times of the year. This even gave an account for their retrograde motion – an illusionary change in the movement of planets through the sky.

There is no clear proof an finding about who built it, but it dates to some time between the third and first centuries B.C., and could possibly be one of the work of Archimedes. The gearing technology with the sophistication of the Antikythera mechanism was not seen again for a thousand years.

Like these a vast majority of these works were lost to history and time and our scientific awakening is delayed by millennia. As a tool for introducing scientific measurement, the techniques of Eratosthenes are comparably easy to perform and require no special equipment, allowing to those who are just beginning their interest in science to understand by doing, experimenting and observing ultimately, following in the footsteps of some of the early great  scientists.