The word astronomy comes from two Greek words : Astron meaning star and nomos meaning law .
Astronomy Is the branch of science that deals with the study of the origin , evolution, composition , distance and the motion of all objects and scattered matter in the universe.
Universe , means totality of space and time together with matter and energy.
Astronomy is a very old science. The ancient Babylonians and Egyptians kept astronomical records mainly for practical purposes. Examples of these are
- Stars which appeared fixed in the sky were used by nomads and travellers to tell direction
-The sun's apparent north - south motion across the sky was associated with the change of the seasons .
The first truly scientific astronomers were the ancient Greeks. The principal phenomena which they tried to explain were :_
(1) The shape and position of the earth in relation to other heavenly bodies .
(2) The diurnal (day and night) motions of the heavenly bodies .
(3) The east ward motions of the planets and stars .
As early as 600BC , through the work of Hipparchus, the view had changed to the one still held today , that means the earth is spherical. Claudins Ptolemy (140AD) considered the earth to be stationary , while the sun , moon and planets all moved around it .
His Fundamental assumptions were
(a) The sun ,the moon , planets and stars revolved in circular orbits ( paths ) around the Earth . The earth was at the centre of the system and was stationary
(b) Each heavenly body revolving around the Earth was contained in an imaginary sphere centred at the Earth .
(c) Each revolving body moved around the Earth at uniform speed .
This geocentric theory could account for the following:_
-The occurrence of day and night , it was proposed that the outermost sphere revolved from east to west in 24 hours , carrying along with it all the inner spheres .
-Observations in the sky _ The ancient astronomers observed the motions of some the planets and their changes in brightness
The geocentric theory was based on religious , beliefs , observations and common sense. There was simply no direct evidence to suggest that the earth is in motion .
Also it was assumed that all heavenly bodies are attracted towards the the Earth .
As the observations of the heavens increased in accuracy due to invention of the telescope and better clocks it was found that :-
- The motion of the heavenly bodies were not uniform
-Jupiter had four moons that circled around it
These observations could not be explained on the basis of the geocentric theory .
Heliocentric theory ( sun centred theory )
According to him it was the sun and not the Earth that was stationary at the centre of the universe. All other heavenly bodies, including the earth , moved around it in circular orbits while rotating about their own axes .This theory could explain convincingly the occurance of day and night . At any moment it is day time for the half surface of a planet that is facing the sun and it's night-time for the other half .
The Importance of Astronomy in Everyday Life
1:It was the earliest method of measuring time enabling us to develop calendars that made it possible to predict the seasons.
2:It is used in navigation, thus it helps us to understand the earth and the modern life .
3:It presents a new frontier for exploration , thus helps promotes the improvement in science and technology due to the need for the study of the universe.
3:It makes easy to locate places on earth by the use of satellites GPS and other heavenly bodies in the universe.
4:Astronomy help us to know the origin of the universe and hence it enhance a new study and prepare for the upcoming events in the universe.
5:It open another wide field for scientists to research thus creating employment and other social and benefits.