The History of Astronomy

Introduction

Astronomy is regarded as one of the oldest sciences, with historical records of the cosmos

dating back around 5000 years ago in Mesopotamia. However, contrary to popular belief,

astronomy consists of more than mapping stars into constellations. It is fundamentally the

study of the entire universe as we know it, its contents and its history. So the main question

arises, how did the study of the cosmos come to be, and how far have we come since then?

To answer that, let us travel back to the Mesopotamian era, 5000 years ago.

The Very Beginning

Many early cultures identified celestial bodies to be with gods, and believed that their

existence and movements are related to natural phenomena such as rain, droughts and

seasons. These observations were made by naked eye, especially since the telescope was

only made in the early 17th century. Moreover, early astronomers are commonly believed

to be priests due to the belief that these celestial objects are manifestations of divine

beings.

The calendars we use nowadays have all developed from early astronomers and their

observations of the movements of the Sun and Moon. At around 2000 BCE, people of

Ancient Egypt and Mesopotamia had used solar and lunar calendars, and are thought to be

the first to do so. Consequently, The Julian calendar (45 BC) was proposed after developing

those older calendars, following the time taken for the Moon to go from a full-moon to the

succeeding full-moon. These measurements of lunar and solar movements had been

tracked using sundials by the Romans, by which time was calculated by the shape and size

of the shadows casted onto the instrument.

Many fantastical phenomena have been recorded in the years humans have been

observing the skies. For example, in 185 Chinese astronomers were amongst the first to

document a supernova, the birth of a star. And since then, many supernovae have been

observed, with one occurring in 1054 whose explosion outshined Venus by a factor of 4.

While the fact that our galaxy, the Milky Way, is one amongst trillions of other galaxies is

only a century-old fact, early astronomers had assumed nearby galaxies to be cloudy

regions of our own galaxy. Described as a ‘nebulous smear,’ the Andromeda Galaxy was

first ever documented by a persian astronomer in 964.

Understanding the Solar System

Moving ahead, we get the theories astronomers in antiquity had proposed of the model of

our Solar System. Back then most cultures and astronomers, such as the Ancient Greeks and their most famous philosopher Aristotle, believed that the Sun and every other

astronomical body orbited around Earth. This led to the geocentric model of the Universe

being suggested, with Earth at the centre of the universe.

However, simultaneously, not everybody believed in the geocentric model, and newer

models were suggested as time went on. The first known person to suggest the heliocentric

model of the Solar System was a Greek philosopher Aristarchus of Samos, where our Earth

and the other planets orbit the Sun. This concept was rejected in favor of Aristotle’s more

recognised geocentric model, however, it was later on brought up independently by a

Polish polymath Nicolaus Copernicus in the early 16th century, who also believed in the

heliocentric model. Unfortunately, Copernicus did not publish his findings, as to not risk

facing the criticism from the general public, who strongly believed in the geocentric model.

Some time during 1609, an astronomer named Johannes Kepler, with the help of the

studies of Tycho Brahe, had formulated his Three Laws of Planetary Motion, which for the

first time correctly described the way the planets move through the Solar System.

His laws state:

1. All planets move about the Sun in elliptical orbits, having the Sun as one of the foci.

2. A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.

3. The squares of the sidereal periods (of revolution) of the planets are directly.

proportional to the cubes of their mean distances from the Sun.

Kelper’s laws had fueled Sir Issac Newton’s formulation of his famous law of gravitation

between the Earth and Moon and between the Sun and the planets. It was during the early

17th century that the first telescopes, used as a military spyglass, came into existence and

hearing this, the Italian polymath Galileo Galilei had modified that model into the Galilean

telescope. With this he became the first person to look at celestial bodies using a telescope,

discovering the existence of four of Jupiter’s brightest moons, whose discovery proves that

not all celestial bodies orbit around the Sun.

18th-19th Century Astronomy

Soon after the invention of the Galilean telescope, scientists were all observing and

identifying the different astronomical bodies that were in vicinity. This era of astronomy

consisted mainly of cataloging stars, star clusters and planetary movement. One very

famous documentation was of the Halley’s Comet, made by Edmond Halley in 1705,

through research of data from previous sightings of the comet. With the help of his friend,

Sir Issac Newton, and his laws of motion he had concluded that those sightings were of the

same astronomical object, and also predicted its return in 1758.

Another revolutionary discovery was made by William Herschel in 1781, of the planet

Uranus. The discovery of Uranus led to other findings such as the presence of an asteroid

belt between the orbits of Jupiter and Mars, and the discovery of another type of ‘light’,

infra-red, which was invisible to naked eye. The revelation of infra-red radiation rapidly

increased the development of the field of optics and digital imagery, which increased the

potential of viewing and understanding the universe. Herschel also played a part in

understanding the true nature of nebulae and cataloging them in a list made by Charles

Messier of Nebulae; in turn Herschel’s findings of over 20 years resulted in almost 2500

different nebulae.

By observing the sky, astronomers have devised many different theories that help change

science into the science that we know today. As an example, the astronomer, Joseph

Norman Lockyer, identified the element Helium while studying the composition of the Sun.

The shift in frequency of light received from a moving source, known as the Doppler Effect,

was proposed by physicist Christian Doppler while trying to explain the different colors

binary stars had, which was a wrong deduction. However his theory was far from wrong,

since it was supported by various scientists to be true. Hence it is clear that astronomy has

played a huge role in the evolution of science.

Theory of Relativity and the 20th Century

One key theory that changed the 20th century astronomers’ perspective of the universe

was Theory of Relativity. This debate had been discussed during the years 1905 and 1915,

and its discussion brought the origin of our universe into debate. German-born physicist,

Albert Einstein, played an exemplary role in the development of this theory, and with this

theory he applied it to the whole universe as a whole. Through many discussions and

research, and using the theory of Doppler’s Effect, scientists of that time had concluded

that the universe was in fact expanding.

This finding led to the development of the Big Bang Theory, which states that around 13.7

billion years ago, the universe had started off as a point with infinite density and heat,

which then exploded into a cosmic expansion that was theoretically faster than the speed

of light. After this explosion came to its indefinite end, the composition of the universe

came to exist, the remaining energy from the explosion aided the formation of the light,

atoms and elements we know of. The light formed back then has allegedly shined 380,000

years after the explosion; this light is known as the Cosmic Microwave Background.

While studying the dynamics and movement of stellar and galaxy clusters in 1933, physicist

Fritz Zwicky suggested that there is not enough visible matter in the universe to be able to

gravitationally hold the clusters together. With this suggestion comes the theory of the

universe being made up of visible matter as well as dark matter. Dark matter is composed

of particles that do not absorb, reflect, or emit light, so they cannot be detected by

observing electromagnetic radiation. Einstein showed that massive objects in the universe

bend and distort light, allowing them to be used as lenses. By studying how light is

distorted by galaxy clusters, astronomers have been able to create a map of dark matter in

the universe. All these methods provide a strong indication that most of the matter in the

universe is something yet unseen. However, the existence behind dark matter and energy

leave behind a lot of unanswered questions, to which astronomers continue to investigate.

Today’s Astronomy

So after 5000 years of history, where exactly are we on this extraterrestrial journey? Due to

technological advancements in the 21st century, collecting and documenting data has been

very efficient and it yields images of high quality. In addition to powerful telescopes to help

us see the cosmos, astronomers have developed machines that project different types of

electromagnetic radiation (such as infra-red and X-rays), this advancement has broadened

our ‘vision’ from visible light alone. As technology continues to evolve, which allows for

efficient and effective means of documentation and/or studying, us humans will only learn

more of the mysteries in our universe.

Demuni Lihini Nivarthana De Zoysa

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Citations

Canadian Space Agency. “A brief history of astronomy.” Canadian Space Agency,

Gouvernement du Canada, 31 Aug. 2021, https://www.asc-

csa.gc.ca/eng/astronomy/basics/brief-history-astronomy.asp#shr-pg0. Accessed on 16 Sep.

2021.

“History of astronomy.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 2017,

https://www.britannica.com/science/astronomy/History-of-astronomy. Accessed on 16 Sep.

2021.

“Kepler's laws of planetary motion.” Encyclopædia Britannica, Encyclopædia Britannica, inc.,

2017, https://www.britannica.com/science/Keplers-laws-of-planetary-motion. Accessed on

17 Sep. 2021.

7

Feed My Curiosity, director. “The Evolution of Astronomy, Chapter 1: The Very Beginnings.”

YouTube, YouTube, 2 Nov. 2018, www.youtube.com/watch?v=mE9DSiRZ3SQ. Accessed on

17 Sep. 2021.

Howell, Elizabeth. “What is the Big Bang Theory?” Space.com, Space, 17 May 2021,

https://www.space.com/25126-big-bang-theory.html. Accessed on 17 Sep. 2021

Photo by NASA on Unsplash, 07 Feb. 2016. https://unsplash.com/photos/Yj1M5riCKk4.

Accessed on 16 Sep. 2021.