LECTURE NOTE ON INTRODUCTION TO ASTRONOMY AND ASTROPHYSICS BY AGBAJOR K. GODWIN DEPARTMENT OF INDUSTRIAL PHYSICS, MICHAEL AND CECILIA IBRU UNIVERSITY, DELTA STATE COURSE CODE: PHY 204 TOPIC: NEWTONIAN MECHANICS (PART 3) LEARNING OUTCOME: At the end of this lesson, the students should be able to distinguish between astronomy and astrophysics. An Overview of Astronomy and Astrophysics The word ‘astronomy’ is an extract of the Greek words ‘astron’ meaning ‘star’ and ‘nomos’ meaning ‘law’ or ‘culture’. The two terms astronomy and astrophysics may be used interchangeably but basically, astronomy refers to the study of objects and matter outside the earth’s atmosphere including their physical and chemical properties while astrophysics refers to the branch of astronomy which deals with behaviour, physical properties, dynamic processes of celestial objects and phenomena. By definition, astronomy is a natural science which deals with the study of celestial objects such as the stars, planets and galaxies and such phenomenon originating outside the earth’s atmosphere such as cosmic background radiation. Astrophysics is concerned with the evolution, physics, chemistry, meteorology and motion of celestial bodies as well as the formation and development of the universe. Divisions of Astronomy Astronomy can broadly be divided into two main branches namely observational astronomy and theoretical astronomy or astrophysics. While observational astronomy focuses on the acquisition of data from the observations of celestial bodies with the use of such instruments like telescopes and spacecraft and analysing the acquired data using the basic principles of physics, theoretical astronomy on the other hand, is oriented towards towards the development of computer or analytical models to describe astronomical objects and phenomenon. Observational Astronomy The major source of information in astronomy is electromagnetic radiation. Observational astronomy may be divided according to the observed region in the electromagnetic spectrum. While some parts of the spectrum may be observed from the earth’s surface, other parts can only be observed either from high altitude or space. The following are some of the subfields of observational astronomy. 1. Radio astronomy 2. Infrared astronomy 3. Optical astronomy 4. Ultraviolet astronomy 5. X-ray astronomy 6. Gamma-ray astronomy. Astrometry and Celestial Mechanics Astrometry is the field of astronomy which deals with the science of measurement of the positions of celestial bodies or objects. Accurate knowledge of the positions of the sun, moon, planets and stars is very essential in celestial navigation and in the making of calendars. Celestial mechanics is the science concerned with description of the motion of natural bodies such as the stars and planets in space. Subfields of theoretical astronomy 1. Solar astronomy 2. Planetary science 3. Stellar astronomy 4. Galactic astronomy 5. Extragalactic astronomy Cosmology Cosmology is the study of the study of the universe as a whole. Observations of the large-scale structure of the universe is very important in providing a deep of the universe. The branch of cosmology which deals with the observation of the universe based on a large scale is known as physical cosmology. Fundamental to modern astronomy is the well-accepted theory of the big-bang, where the universe is considered to begin at a single point in time, and in the process of time, expanded over many billions of years to its present condition. .