Use this tag for questions pertaining to how we can observe astronomical objects, as well as for what physical limitations are encountered. This can include, for example, questions about
- How large a telescope is needed to observe a particular object;
- How the atmosphere interferes with astronomical observations;
- Which phenomena can be detected in radio waves, or gamma rays; or
- The particulars of photometry, spectroscopy, or interferometry as employed in astronomy
are suitable for this tag.
On the other hand, questions only concerned with the data itself, rather than the acquisition of that data, should probably be tagged astronomy and not observational-astronomy. Similarly, if one is only concerned about underlying physical theories, astrophysics would be more appropriate than observational-astronomy.