A Brief History of Astronomy

Indian and Arabic Astronomy

(500 to 1200)



In India, Aryabhatta, writes a book in which he states that the Sun is the centre of the Solar System. This idea would not be accepted for another 1000 years.


Varahamihira writes that "Bodies fall towards the earth as it is in the nature of the earth to attract bodies", 1100 years before the idea would become accepted.



The Arab mathematician, al-Khwarizmi, adds and refines Ptolemy's geographical knowledge, using astronomical observations to give the latitudes and longitudes of over 2400 localities in Europe and Asia.

He also championed the use of the Indian number system working out the rules of arithmetic that would simplify calculation. His numbers arrived in Europe where they became known as Arabic Numerals.



The length of the year is calculated as 365 days 5 hours 48 minutes 24 seconds by the Arab astronomer, al-Battani. At that time (and for the next 600 years) Europe's calendar is based on a year of 356 days 6 hours.

Al-Battani also updates the figures for the Precession of the Equinoxes (54.5'' per year) and the tilt of the Earth's axis (23° 35').

His observations show that the Earth's distance to the Sun varies, putting a doubt on the idea of perfect circular orbits.


al-Sufi publishes a book about stars listing a number of objects that are hazy and fuzzy. These turn out to be the star clusters and galaxies that will provide the information to enlarge the size of the Universe, 900 years later.

This is the first written mention of the object that would later be known as the Andromeda Galaxy.

al-Sufi's Book
al-Sufi's Book



The Central Asian scientist, al-Biruni, develops the experimental method of science including the modern mathematical treatment for handling errors.

His surveying techniques using triangulation allow him to measure the radius of the Earth as 6339.6 km, a value that would not be improved for 500 years.

He suggests that the velocity of light is immense compared to that of sound. He theorises that the appearance of the Milky Way is due to it being made up of countless stars, an assertion that would not be verified until the invention of the telescope 500 years later.

al-Biruni's measurement of the radius of the Earth
al-Biruni's measurement of the radius of the Earth



al-Zarqali (known in the West as Arzachel) discovers that the point in the year when the Earth is closest to the Sun moves forward at a rate of 12.04'' per year. This is within 2% of the modern value. He also suggests elliptical orbits for the planets.


al-Khazini suggests that the centre of the Earth is the source of all gravity.

Ptolemaic System
The Ptolemaic Geo-centric (Earth Centred) System


Many Greek and Arab books are translated into Latin including Ptolemy's Almagest. The influx of classical knowledge helps the Renaissance begin in Europe.

The (Christian) Catholic Church adopts Aristotle's cosmology. In the coming centuries, disagreement with this cosmology would become a heresy.

The model enlarges Aristotle's ideas of the corrupt Earth and the perfect heavens. The most corrupt part of the Universe is Hell which is situated in the centre of the Earth. Both Earth and Hell are imperfect and both are subject to change, corruption and decay. Man's Sin causes the corruption of the Earth. Above the Earth is the atmosphere. This is less subject to change but changes enough to produce the weather. Aurora, meteors and comets are also considered to be atmospheric phenomena.

The Moon being further from the Earth, changes less. It changes its phases and has a blotchy appearance but has the perfect circular motion of a celestial object. The Sun and planets come next. They don't change and also move in circles around the Earth. Most distant is the crystal sphere containing the stars. The stars are unchanging and eternal. God (the most perfect part of the Universe) is on the outside of this final crystal sphere. All heavenly motion is in circles (a perfect shape) or 'circles within circles'.

Dante, would later write about descending the nine circles to Hell and ascending the celestial spheres to God.

Based on Biblical chronologies, the Earth and the Universe were considered to be only a few thousand years old.

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KryssTal Related Pages

An easy-to-understand scaling of the Universe in space. Distances in space are represented by the time light takes to travel there.

An easy-to-understand scaling of the Universe in time. The chronology of the Universe is compared to a real year.

A listing of the 20 brightest stars as well as explanations of the terms used.

Information about the planets and satellites of the Solar System with explanations of the terms used.

A historical account of the discovery of the electromagnetic spectrum and its uses in Astronomy. Radio waves, infra-red, visible light, ultra violet, X-rays and gamma rays are explained.

An account of how various properties of stars can be measured by studying starlight. Includes brightness, distance, luminosity, temperature, mass, radius, density and an introduction to the H-R Diagram.

An account of how stars evolve and change the chemistry of the Universe.

The force that moves apples and planets. A short introduction to the ideas of Kepler and Newton that culminated with the theory of Universal Gravitation.

This looks at the history of inventions and the various civilisations of the world.

Selected biographies of people from around the world including scientists and astronomers.

External Links

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History of Science A large collection of resources looking at the history of astronomy, physics, chemistry and mathematics.