A History Of Astronomy

Stars of the Ancient Skies: Astronomy’s Roots

The roots of astronomy go back to the dawn of mankind. When he first looked up and wondered about the stars. He saw that the stars stayed where they were but moved across the sky as they night progressed. These movements of the stars, he noted, coincided with the times of the year. Ancient astronomers also noted ‘visitors’ to the nights sky. The planets and comets.

In this early period astronomy as we know it, did not exist. Farmers and sailors used the stars to navigate the seas and plant their crops. To help with this they started dividing up the sky into constellations. These early constellations were not the ones we know today, todays constellations have their roots in Greek and Roman Mythology.

The early civilisations started to record the stars and the events that happened. Many of these records survive today. The Chinese were great recorders and is a great source of information to modern astronomers. In the Middle East the Babylonians also kept records and these can be married with the Chinese records giving a wealth of information about the astronomical events of thousands of years ago. But it was the Greeks who first put together some of the constellations we know today. Like their predecessors, the Chinese and Babylonians, they also noted that the Sun kept within twelve of these constellations. These constellations became the constellations of the Zodiac. All these civilisations also recorded stars which also kept to the Zodiac. They called them ‘wanderers’, to which we get our word ‘planet’ from. These planets were given names which we still use today.

There are many early astronomers that studied the stars and tried to understand their meaning. But I have chosen three figures whose contribution to Astronomy, Aristotle, Hipparchus and Zhang Heng.

Aristotle viewed the sky as celestial spheres, with the Sun, Moon, Planets and stars set in these concentric spheres. He viewed the Earth as the centre of the Universe. This view prevailed until the 16th century that Johannes Kepler showed that the Earth revolved around the Sun.

Hipparchus was a Greek Mathematician and Astronomer. His contribution to Astronomy was to show the Procession of the Equinoxes. He worked out the length of the Tropical Year, the time the Sun takes to make one passage through the Ecliptic. Using observations that he had made and others made going back from the 5th to 3rd Centuries BCE. His final calculation is only 6 minutes from the accepted time today. He also worked out the times of the Winter and Summer Solstice’s and the Spring and Autumn Equinox’s.

My final choice is the Chinese Astronomer Zhang Heng. who lived between 78 and 139 AD. He proposed that the universe was egged shaped and the yolk was the Earth. This was very similar to the geocentric universe proposed by Aristotle and Hipparchus. Zhang Hang also compiled one of the first catalogue of stars. His catalogue contained over 2,500 stars, more than any of the catalogues produced by Greeks.

The Renaissance Rebirth: Astronomy’s Enlightenment

Until the 16th Century the common assertion was that the Earth was flat and the Universe revolved around the Earth. This belief was fostered by the Church and any person trying to prove otherwise was deemed a heretic and executed.

However, the Renaissance, which covered the period between the late 14th and 16th Centuries, was making its way through Europe. It affected all aspects of life including the Sciences and Mathematics. It was a time when knowledgeable people, like Scientists who started to challenge these long held beliefs. As early as the 14th century there were people who started to question the beliefs of the day. Those questioned whether the Sun, not the Earth, were centre of the Universe. Others questioned whether Earth was flat or not. In fact it was first proposed by Aristotle back in 350 BCE. Pythagoras back in the 6th Century BCE who also proposed that the Earth was round based on his observations of Lunar Eclipses.

With the invention of the telescope back in the 16th century astronomers were able to see the shape of some of the planets. These planets were shown as round objects against the background of the starry sky. From his observations Galileo proposed that the Earth was also round. This put him on a collision course with the Church, just like so many of his contemporises. The invention of the telescope and how it changed the World can be found at my post ‘How the telescope changed the world’.

With this ‘Scientific Enlightenment’, as it was called, there were many scientists who paved the way for this ‘Enlightenment’. I want to briefly talk about four of these scientist whose work provided the basis of astronomy today. I have a separate category designated to these, and others, where I have talked about their lives in more detail.

Nicolas Copernicus :- 1473 to 1543.

Copernicus formulated a Sun centered Universe, or Heliocentric universe. He independently arrived at this model even though it was put forward by the Greek mathematician Aristarchus of Samos nearly 18 centuries earlier. His model was the basis for future concepts of the Universe.

Tycho Brahe:- 1546 to 1601

Tycho Brahe’s contribution to this period was to make accurate positions of the Stars. At the time the teaching was that the Earth was the centre of the Universe, but Copernicus Heliocentric Universe was starting to be accepted. but still the Moon, Planets and Stars were fixed on celestial spheres which were never changing. His observations and records contributed to the Heliocentric idea of the universe. This unprecedent work of Tycho Brahe led to Astronomy being turned into the first modern science.

Johanne Kepler:- 1571 to 1630

Johannes Kepler was a German mathematician and considered to be the fonder of modern astronomy and influencing later scientists, like Isaac Newton. Kepler worked under Tycho Brahe and using Brahe’s records and observations led Kepler to develop his ‘Laws of Planetary motion’. These ‘Laws’ were not well received by his peers as it went against the teachings of the Church at the time which taught that the Earth was at the centre of the Universe and the sky did not change.

Galileo Galilei:- 1564 to 1642

Galileo is often credited with the invention of the telescope, this was however a misconception. . The first top demonstrate the principle of a telescope was a Hans Lippershey in 1608. He built a telescope with a 3x magnification. Lippershey tried to patent this in the Netherlands but was unsuccessful. Based on uncertain details and descriptions Galileo built the first first refracting telescope.

With this telescope, he observed the Moon and noted its craters and mountains. In 1610 he observed Jupiter and noted three stars close to Jupiter. Over subsequent months he noted that the three points of light were joined with a fourth one and together they “did a dance” around Jupiter. He concluded that these points of light must be moons orbiting Jupiter. This observation was another ‘nail in the coffin’ for the Earth centred and unchanging Universe. These four moon were to become known as the ‘Galilean Moons’ in his honour.

Sir Isaac Newton:- 1642 to 1726

Sir Isaac Newton is well known for his theory of gravitation. But the story of him watching an apple fall from a tree he was sitting under is considered a myth or possibly a extension of the truth. He may well have witnessed an apple or other object falling to the ground and asked himself the question “why does it fall like this”. Newton’s theories on these motions led him to develop ‘Newton’s Three Laws of Motion’. Which are still taught in science classes today. Newton also developed the reflector telescope which is widely used today.

Advancing the Final Frontier: Modern Astronomy’s Leap

For those that followed these early scientists, found new ways to observe the Universe. Improvements in telescopes and observational skills led to more accurate and exciting work.

Prior to Isaac Newton, Astronomy and Physics had been relatively separate teachings. However, as the 19th century began the study of astronomy and related aspects of Physics merged to form Astrophysics. The understanding of optics and light led to the advancement of the telescope. One man who’s pioneering work led to this advancement was William Herschel. He improved upon the telescope of Sir Isaac Newton. He perfected the art of mirror making and also improved optics used to make eyepieces as a whole. These eyepieces were never really improved upon until the 20th century.

Herschel used his telescopes to map the sky and record ‘pairing of stars’ as they were known at the time. The understanding that two or more stars could revolving around one another was not the accepted idea of the time. Though some astronomers had proposed the idea.

In 1781, using his six and a half inch reflecting telescope Herschel came upon a disk. Not knowing what this was he he took notes over several nights and sent them to his friend, Nevil Maskelyne, the Astronomer Royal. The Russian mathematician, Anders Lexell, then from Herschel’s observations computed that the object orbited beyond Saturn and was therefore a new planet. Herschel at first named the planet after the King but it officially became known as Uranus.

As the 19th century began to close the new invention of the camera began to be used in astronomy. Early photographs were done on glass. The further development of the emulsions used in the film led to the amateur astronomer being able to photograph the sky themselves. During the early part of the 20th century film cameras were developed further. The glass plates that were originally used in the late 19th to mid 20th centuries were replaced by cameras that could record finer detail. The late 20th saw the introduction of DLSR cameras. This type of camera allowed the astronomer to take much longer photographs. This development has led the amateur astronomer taking their own photographs.

During the early 20th century radio astronomy was also taking off. In 1930 Karl Jansky, noted a continuous hiss at the short end of the radio spectrum. Following measurement he concluded that this ‘hiss’ was coming from the centre of the galaxy and radio astronomy was born.

Astronomy Today: Peering into the Cosmos with Cutting-Edge Technology

Today a vast range of telescopes peer at the Universe trying to understand its mysteries. These range from ground based telescopes to orbiting telescopes like the Hubble Telescope and the James Webb Telescope. From observing the universe in the visible spectrum to infra-red, x-ray to radio astronomy, all the spectrum has mysteries that remain to be answered. Who knows what answers await us and new mysteries to solve in the future.