List of unsolved problems in astronomy
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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.
This is a dynamic list and may never be able to satisfy particular standards for completeness. You can help by adding missing items with reliable sources.