List of unsolved problems in astronomy

This article is a list of notable unsolved problems in astronomy.

Problems may be theoretical or experimental.

Theoretical problems result from inability of current theories to explain observed phenomena or experimental results.

Experimental problems result from inability to test or investigate a proposed theory.

Other problems involve unique events or occurrences that have not repeated themselves with unclear causes.

Rotation curve of a typical spiral galaxy: predicted ( A ) and observed ( B ). Can the discrepancy between the curves be attributed to dark matter?
Estimated distribution of dark matter and dark energy in the universe