Cosmology Astronomy

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Introduction to Astronomy and Cosmology

Astronomy is derived from the Greek word ‘ἀστρονομία’, where ἀστρον or Astron means ‘star’ and νομία or nomia from νόμος (nomia), which literally means the law or culture of stars.

It is a science that studies the laws of the stars, i.e., everything outside the Earth’s atmosphere.

Cosmology is derived from the Greek word κόσμος, where kosmos mean "world" and -λογία, or -logia means "study of").

For studying the science behind the origination and development of the universe, we use the term ‘cosmology’. However, cosmology is a branch of astronomy that studies the Universe as a whole.

Cosmology Astronomy 

This page will provide the introduction to astronomy and cosmology, cosmology astronomy, basic astronomy and cosmology, astronomy astrophysics cosmology, and extragalactic astronomy and cosmology in detail.

Now, let’s understand astronomy and cosmology in detail:


In 1656, the term cosmology was first employed in an English dictionary named Thomas Blount's Glossographia.

In the year 1731, the term ‘cosmology’ was carried to in Latin by a German philosopher named Christian Wolff, in Cosmologia Generalis.

Cosmology is focused on studying the origin and evolution of the universe, from the Big Bang to today and on into the future. It applies a scientific approach to study the origin, evolution, and eventual dismissal of the universe. 

One of the types of cosmology is Physical cosmology. It is the scientific study of the origin of the universe, its large-scale structures and dynamics, and its ultimate dismissal, as well as the laws of science that govern the areas mentioned above.


All the celestial objects residing in space have their significance and to study these, we use the term ‘astronomy’.We use astronomy word as terminology to study the science of celestial objects, space, and the physical universe. 

It is one of the oldest natural sciences that studies celestial objects and their processes. The objects may include all the planets, moons, stars, galaxies, nebulae, and comets. 

Astronomy uses mathematics, physics, and chemistry to explain their origin and evolution.

Astronomy allows astronomers to study various ongoing spatial phenomena, and these are as follows:

Supernova explosions, 

Gamma-ray bursts, 



Pulsars, and 

Cosmic microwave background radiation. More specifically, astronomy studies everything that originates outside the Earth's region.

However, cosmology is a term that takes into account the theory behind the building of the universe and modern cosmology is the next step after the Big Bang Theory.

Astrophysics Astronomy Cosmology

The ancient period recorded history made methodical observations of the dark sky; these include the following:

  • Babylonians

  • Greeks

  • Indians

  • Chinese

  • Egyptians

Maya, and many more ancient diligent Americans.

In the ancient period, astronomy involved various disciplines like celestial navigation, astrometry, observational astronomy, and the preparation of calendars. Nowadays, professional astronomy is said to be akin to astrophysics.

Professional astronomy is divided into two branches, viz: observational and theoretical. 

Observational astronomy focuses primarily on gathering data by observing astronomical or celestial objects and this data is then analyzed by using basic astronomy and cosmology principles of Physics. 

However, theoretical astronomy is centred on the development of computer or analytical models to study and describe astronomical objects and their phenomena. These two fields complement each other. This part tries to explain observational results and observations are used to affirm our theoretical results.

So, basic astronomy and cosmology talk about the things mentioned above. 

Astrophysics Astronomy Cosmology

“Astrophysics" and "Astronomy" are synonyms to each other. According to the dictionary definitions, "astrophysics" refers to the branch of astronomy that deals with "the behaviour, physical properties, and dynamic processes of celestial objects and phenomena, while "astronomy" is "the study of all the around the Earth's region and the study of their physical and chemical properties using Physics, Chemistry, and Mathematics. 

Extragalactic Astronomy and Cosmology

Extragalactic Astronomy and Cosmology is a book written by Peter Schneider. This book is very useful for Aeronautical Engineering students and also for those who have an interest in developing their knowledge in the field of Spacecraft and Space Engineering.

Observational Astronomy

Visible light is the main source of information about celestial bodies and their processes, or more specifically the electromagnetic radiation. 

Observational astronomy can be subdivided into fields according to the corresponding region of the electromagnetic spectrum on which the observations are made. We can observe a few parts of the spectrum from the Earth's surface, while other parts are observable from either great heights or outside the Earth's atmosphere. 

Specific information on the subfields of observational astronomy is given below.

Following are the types of observational astronomy:

  • Observational astronomy

  • X-ray astronomy

  • Radio astronomy

  • Infrared astronomy

  • Optical astronomy

One of the historical methods of astronomy is optical astronomy; let’s understand it in detail:

Historically, optical astronomy is also known as visible light astronomy. We call it one of the oldest forms of astronomy. Images of observations were initially drawn by hand; however, in the late 19th century and most of the 20th century, images were prepared using photographic equipment. 

At present, the images are made by using digital detectors, particularly charge-coupled devices or CCDs, and then recorded on modern mediums. Though visible light extends from approximately 400 nm to 700 nm, we can use the same equipment to observe some near-ultraviolet and near-infrared emissions.

FAQ (Frequently Asked Questions)

1. Describe the Two Subfields of Observational Astronomy.

Ans - 

1. Ultraviolet Astronomy 

Ultraviolet astronomy uses ultraviolet wavelengths approximately between 10 to 320 nm. Light at these wavelengths is absorbed by the Earth's atmosphere, for making observations at these wavelengths can be done from the upper atmosphere or from space. UV astronomy is well suited to the study of thermal radiation and spectral emission lines from hot blue OB stars that are very bright in this waveband. It also includes the blue stars in other galaxies that have been the focus of several ultraviolet surveys. 

Other objects observed in ultraviolet light include planetary nebulae, active galactic nuclei, and supernova remnants.

2. Radio Astronomy

Radio astronomy makes the use of radiation with wavelengths greater than one millimetre,  i.e., outside the visible range. Through radio astronomy, it is easy to measure both the amplitude and phase of radio waves, while it is not easy to do for shorter wavelengths.

2. Define Extragalactic Astronomy.

Ans - Extragalactic astronomy studies the objects outside our galaxy. It is a branch of astronomy that is concerned with the formation and evolution of Galaxies, their description and classification, the observation of active galaxies, and at a larger scale, the groups and clusters of galaxies.

Most galaxies are organized into various shapes that allow for classification schemes. They are commonly categorized into elliptical, spiral, and irregular galaxies.

An elliptical galaxy has an elliptical cross-sectional shape. The stars make Brownian orbits with no specified direction. These galaxies contain little or no interstellar dust, few star-forming regions, and very old stars. Elliptical galaxies are most specifically found at the core of galactic clusters and are supposed to be formed through mergers of large galaxies.