What is Astronomy?
Astronomy is the scientific study of matter in the external parts of the atmosphere of the Earth including stars, planets and what they are made of and lastly how they move.
Early indigenous knowledge
- lunar calendar
- solar calendar
- star lore
Astronomy is one of the sciences that having lived for a long time. Ancient civilisations globally observed over a period of time the night skies, noting the patterns they observed in the sky. These patterns are now known as Constellations.
A constellation is any group of stars, as seen from Earth, that seems to form a pattern or image in the sky. Various nations, culture and people have star patterns and how they explained the meaning of the patterns e.g. a well-known Southern Cross.
The Southern Cross, Crux and the two bright pointers stars were used by farmers to mark the starting point of the planting season. According to Sotho, Tswana, and Venda beliefs, these stars were named Dithulwa, meaning “The Giraffes”. The shining stars of Crux are the male giraffes, and the other two Pointers are female giraffes.
People also observed the change of the stars and planets over the sky marking the passage o time. Early cultures usually identified the stars and planets according to what they observed in the night sky with gods, spirits, or animals. Old astronomers could differentiate between stars and planets as the associated locations of the stars remain the same in the sky while planets arise to move across the sky associated to the background stars. Ancient people knew only Mercury, Venus, Mars, Jupiter and Saturn in all planets. Uranus and Neptune were discovered after telescopes were created.
The ancient civilisations for example, the Sumerian, Babylonians and Egyptian were in charge for the implementation of many constellations that astronomers use in the west today. The ancient Greeks, Australians, Mayans, Aztecs, Polynesians and ancient Chines and Japanese added a particular knowledge of these constellations and were later passed on and people showed interest in the stars and had discovered their own constellations and stories about the stars.
An important role played by the Astronomy in religion is that at time, and the dates of festivals and holy days were fixed by the order of the stars and the phases of the Moon. The ancient Egyptian and Mayan pyramids and temples were constructed in such a way that the natural objects e.g. Sun, Moon and Stars would be visible to the people from the top windows at important times of the year such as solstices and Equinoxes.
Then in our country South Africa, early cultures had their own different constellations ad stories which were then inherited from generation to generation. The early cultures believed that stars provide directions, when travelling to new areas or shipping they were not able to use directions from the landmarks instead used the star. When observed from a certain position, a star rises and sets in the same direction all the time and follows the same way cross the sky. We are quite familiar with some of these ideas as the sun is a star and we always observe it rises and sets in the same direction every day. The rising and setting stars were used as direction to early navigators to find their way.
Early cultures also used to take the observed changes in the sky for timekeeping. A whole full day was noticed by the time between one sunrise and the next, just as it is today. The Moon’s everyday phases made it a very convenient “clock”, and the time period between a full new Moon and the following made the basis of many of the oldest calendars.
The cycle that was useful because it was predictable in the same way as day and night is called a Lunar cycle. However, each moon cycle was related to various season with its own name and activities, the tally sticks with notches attached to them composed of bones have been found together as far back as 20-30 000 years ago and are traditioned to mark the phases of the Moon.
Today the Solar calendar is used, it is a calendar in which a complete revolution of the Earth around the sun said to be one complete year but the lunar calendar is still used by some religious calendars. For farming communities accurate timekeeping was particularly important for people to know when to plant their seeds and when to harvest their crops.
Again the Pleiades, also referred to as Seven Sisters, is a glowing cluster of stars. The Pleiades were used by South Africa traditional farming communities to assist in planning their planting. In June once the constellation was visible in the morning they knew it was time to begin with their planting of crops. Then the Khoikhoi generation also known as the Pleiades Khuseti meaning “rain stars”. (Siyavula,2015 chapter 20.1)
The astronomers who live in the past had no refined observatories. They normally used their own eyes to study the stars and planets, and that was named eye observing. The first observatories were built American Mayans, ancient Egyptians and ancient Chinese, and those building were used for studying stars with no telescopes inside them.
Today the modern observatories consist of telescopes that are large with extremely tense cameras and instruments riding on the telescopes. The computers were used by the astronomers to move the telescope and conduct the instruments. The improvement of technology made it us for us to be able to see a lot more and have learnt a lot more about the Universe.
The largest optical telescope in the Southern hemisphere which is found in South Africa is named, the Southern African Large Telescope (SALT), the telescope is found just outside Sutherland in Karoo where we find clear and very dark skies. The main mirror of the SALT measuring 11 x 9 meters across forms a hexagonal shape that is composed of 91 individual smaller mirrors which are packed together. The mirror is so large in such a way that it can collect a lot of light from very distant and faint objects, and this telescope is also used to study the difference of objects which involves asteroids, stars and galaxies.
To test the laws of gravity u the astronomers planned to use the giant telescope and black holes, and will also study how galaxies form, evolve over time and lastly detect life around the universe. There is a lot to learn about in the universe, but we only have 5% of content of our Universe currently so the SALT and SKA are there to help us to gain more knowledge regarding the Universe.
The ancient Greeks, one of the astronomers believed that the earth was located at the centre of the universe with the planets and stars orbiting around the earth.
In 1543, Nicolaus Copernicus, an astronomer and polish Mathematician implemented his book called the Revolutions of the Celestial Spheres. In the book he claimed that the sun instead of earth was the natural object that was found at the centre of the solar system. “Copernicus correctly ordered all the planets known at the time in increasing distance from the sun”. In the model that he developed all the or its of the planet were spherical and this is similar to the model of the ancient Greeks.
Johhanes Kleper a german astronomer and Mathematician, discovered his model of the solar system to fit the observations of the planet’s movement, also discovered stated that all planets orbited in ellipses (ovals) or the orbiting is elliptical. The earth orbits faster when it is closer to the sun and orbits slower when it is further to the sun.
In 1609 Galileo Galilei an Italian physicist, mathematician and astronomer built the first telescope and was also the first astronomer to use the telescope. He again published his first book called the Sidereal Messenger, discussing the findings he came up with using the telescope. The four largest moons Jupiter named Galilean moons were discovered by him, observing the movement of moons over several nights made him to realise that the moons were orbiting around Jupiter.Again stated that the sun has dark sports named sunspots and the moon has craters.
Lastly in 1929, astronomer Edwin Hubble made an implementation based on his discoveries that the Universe id expanding, he observed the movement of galaxies away from the earth and found that the distant ones were moving away fastest. This means that there is a process of repulsion occurring as the galaxies were moving away from each other, and the space between the grows bigger and bigger. (Siyavula,2015 chapter 20.2)
- Korablev,P. 2005. Study of the planets. Terrestrial and gaseous planets,48(2):626-628.
- Siyavula Technology Science. 2015. Explore. https://www.siyavula.com/read/science/grade-7/historical-development-of-astronomy/20-historical-development-of-astronomy Date of access 02 Mar.2020.