Cosmos

In view of the various (and varying) answers above (3 at the current posting: Sir Cumference, Allure, User123), the relevance of this annoyingly challenging question is established. Nevertheless, the posted answers seem to contradict themselves, if not containing contradictions individually. Even if there seems to be agreement that Cosmology and Astronomy are different, there doesn’t seem to be a clear consensus on how they differ and are related. There may be a vague convergence on the notion that Cosmology is characterized as more holistic (eg “whole”, “bigger/higher”) than Astronomy. One answer even goes as far as saying that Astronomy is “less precisely defined” (implying perhaps that Astronomy can encompass Cosmology, “depending on who you are talking to”).

So let’s assume that the author of this question is looking for clues to decide on his academic future (say which department to enroll in, in a prestigious university that puts Astronomy and Cosmology in different departments). Let’s ask ourselves whether Astronomy SE has answered satisfactorily here? I think we have not completely yet. So let me try to throw in additional arguments and clues.

Are Astronomy and Cosmology the same?

No... But, there are commonalities (which make things confusingly intriguing indeed!)

The ancient Greek invented these two concepts. The following site gives a brief intro

Astronomy in ancient Greek means “laws of the (visible) stars”. Today, we extend this definition to:

The science of the celestial bodies and the Universe, dealing especially with the positions, dimensions, distribution, motion, chemical composition, energy, and evolution of celestial bodies and phenomena. (http://dictionary.obspm.fr/index.php?showAll=1&&search=A&&formSearchTextfield=&&page=41)

Cosmos in ancient Greek means “order (of everything)”. Today, we use it as:

The science of the origin, structure, and evolution of the Universe including the origin of galaxies, the chemical elements, and matter. (http://dictionary.obspm.fr/index.php?showAll=1&&search=C&&formSearchTextfield=&&page=57)

So in ancient Greek, Astronomy is the science that look for the order (the laws governing) in the observations (of the Celestial Sphere). Cosmos designates the abstract whole thing that would be governed by the discovered set of laws. If you know the laws, by definition you can predict the evolution of anything in Cosmos (that Cosmos), visible or not, detectable or not yet detectable. If you don’t know the laws, you can’t predict and it would be Chaos, not Cosmos that is observed.

This begs the question: Has these 2 fields merged today. Put differently, can I specialize in one field, but not the other?

The answer is no, they haven’t merged (yet). As an example, Stephen Hawkins has never been described as an astronomer. Wiki describes Carl Sagan as both an astronomer and a cosmologist (among other qualifications), which seems to indicate that the two fields are getting closer, or at least very closely related. It would be difficult to specialize in one while having only casual knowledge of the other.

Another clue to support this answer that Astronomy and Cosmology are different fields of researches, but increasingly related, is that last year’s Nobel prize in Physics was rewarded to 3 scientists:

(Sir) Roger Penrose, a mathematician and cosmologist. Andrea Ghez, an astronomer. Reinhard Genzel, an astrophysicist.

As a closing note, we use “astronaut” and “cosmonaut” interchangeably (taikonaut for the Chinese). Which seems to defeat the answer that the 2 terms are different. In fact, it may indicate that, for these _nauts, the difference is irrelevant. All they need is to master the overlap of the 2 sciences.