While retagging, I get confused a lot as: "which is which". This is bugging me for a while...
For now, the tag wiki definition of astronomy -
Astronomy is a natural science that deals with the study of celestial objects (such as stars, planets, comets, nebulae, star clusters and galaxies) and phenomena that originate outside the atmosphere of Earth (such as cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.
And, for astrophysics -
Astrophysics: Physics related to astronomical objects: stars, galaxies, nebulae, globular clusters, clusters and super-clusters of galaxies, white dwarf stars, neutron stars and pulsars, black holes, the inter-stellar medium, non-terrestrial planets, ring systems, MACHOs, the inter-galactic medium, the great voids, quasars, etc...
Looks like both the tags are having the same definition except that Astronomy is having additional objects like "planets" and Astrophysics is not... From the current definition of both tags, I see that astronomy is dealing with a lot of things than astrophysics...
Let's have a look at cosmology now...
The study of the large-scale structure, history, and future of the universe.
Sometimes, we could give this kind of definition from the last sentence of astronomy wiki def. Because, it covers the history and future with a single word
astrophysics + cosmology = astronomy
But, I don't like these tags to be inter-linked with each other. Each should have an unique definition. So, I've got three choices:
- We can use astronomy for observational purposes by merging astronomy under observational-astronomy and not the other way round. Now, Astrophysics and cosmology could be set free. I mean, all would've got different meanings.
- If we wanna keep observational-astronomy, then - we should necessarily merge the other two (astrophysics & cosmology) under astronomy.
- This is the best choice I like. We redefine all the tags, or atleast astrophysics and astronomy and finally arrive at a definition for the observational-astronomy