This section is included as an aid to a beginner in X-ray astronomy who wishes to start the learning process by using a “good” source – one where adequate data can be guaranteed and no unusual circumstances make analysis difficult. For example, although Sco X-1 was the first X-ray source beyond the Solar System ever detected, it is so bright that it can be observed with modern detectors only in extremely unusual modes, making it a poor choice for today's beginner. The sources listed here have been regularly observed by numerous satellites in normal modes of operation and should provide good “test” cases for beginners. That said, there is nothing stopping observers from requesting observations even of common sources in unusual modes, so care should be exercised when selecting an observation.

Point sources

Although they may have some intrinsic extent, the sources in Table A3.1 are all point sources as far as past and current X-ray telescopes are concerned. Observations of these sources may or may not involve gratings; this must be determined on an observation-by-observation basis.

Diffuse sources

All of the sources in Table A3.2 are diffuse sources of varying extent. Some (such as the Cygnus Loop) will fill the FOV of any X-ray detector, while others (e.g. Cas A) will generally fit within the FOV of most instruments. Sources within the Solar System, such as Jupiter, move too rapidly for X-ray satellites to track them.