What is the main difference between Astronomy, Astrophysics, and Cosmology?

I have the impression that astronomy is a subject that runs parallel to physics but it is outside the physics field. This is based on the division of departments present in many universities: the department of physics being separated from the department of astronomy. The difference between cosmology and astrophysics is more obscure to me. I have the impression, though, that cosmology is more concerned with the structure of spacetime and universe models while astrophysics is more concerned with stellar life cycles, physical properties of stars, galaxies etc.

Which is the field that had more activity/ scientific breakthroughs recently?

In real life, are those classifications even important? Are there many differences between the education process of a future astronomer, astrophysicist or cosmologist?

Somebody, please, give examples of famous astrophysicists, cosmologists and astronomers at the present time.

  • $\begingroup$ Astronomy is not outside physics, it is one of the many subfields of physics. $\endgroup$
    – Kyle Kanos
    Nov 22, 2014 at 13:51
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    $\begingroup$ Astronomers do the observational part: they look out into the universe through a telescope, and classify what they see. Astrophysicists will then try to explain these observations using the known physical laws, which is what has led to our understanding of the inner workings of stars. Finally, cosmologists will try to explain the evolution of the universe as a whole: how did the big bang happen, and how did the universe evolve into what it is today. $\endgroup$
    – jabirali
    Nov 22, 2014 at 13:51
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    $\begingroup$ Also, have you bothered to check the Wikipedia entries on Astronomy, Astrophysics, and Cosmology? These pages are just loaded with information describing the fields (e.g., what they study). $\endgroup$
    – Kyle Kanos
    Nov 22, 2014 at 13:57
  • $\begingroup$ The wikipedia descriptions could be quite different from the perceptions of the scientific community. I doubt that in real life the works of astronomers, cosmologists and astrophysicists obey the boundaries fixed by the cold definitions of a wikipedia page. Also, they wouldn't answer the remaining questions; specially the third one. $\endgroup$
    – Yhoa
    Nov 22, 2014 at 14:10
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    $\begingroup$ The last question is not a physics question.Could be asked in chat once you get enough points $\endgroup$
    – anna v
    Nov 22, 2014 at 15:31

2 Answers 2


Richard Feynman has nice words about science. It is not bad to read chapter 3 of "Feynman Lectures on Physics". The main point of his lecture is that "there is no strict boundary between different fields of science", "nature doesn't concern what we call its parts!"

So, we can't look for a line that divides celestial works into astronomical or astrophysical or cosmological. Although the main keywords about these fields are respectively: "observation of celestial bodies", "machinery of celestial bodies", "evolution of cosmos as a whole". Surely, they use findings of each other.

Recently, cosmology has encountered with big questions, really big! Dark matter and dark energy are the most challenging ones. But it is interesting that if there weren't astronomers and their numerical data, cosmology could not progress.

Usually the students of astronomy focus on classical mechanics and optical methods to be able to observe celestial bodies. Astrophysicists concern general relativity and nuclear physics as two important tools to describe stars or galaxies. But cosmologists are interested in modern theories too, especially string theory. Therefore the courses which they pass should be related to these subjects.


Astronomy talks about celestial objects (such as stars, galaxies, nebulae etc) and celestial phenomena (such as gamma ray bursts etc), their position, motion, evolution, chemistry, physics.

Astrophysics is a sub-branch of astronomy to deal with physics of celestial objects and phenomena. The first encounter: A guy put microscope in front of rainbow spectrum of sunlight just to see black bands between colors. The explanation waited for very long which required quantum physics to come.

Cosmology talks about universe as a whole which includes origin, evolution and ultimate fate of the universe.


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