Explanatory power is the ability of a hypothesis or theory to explain the subject matter effectively to which it pertains.
He describes how very specific, and even somewhat falsifiable theories were provided to explain how the god Demeter's sadness caused the seasons.
Alternatively, Deutsch points out, one could have just as easily explained the seasons as resulting from the god's happiness, which would make it a poor explanation because it is so easy to arbitrarily change details.
None of the details about the Earth rotating around the Sun at a certain angle in a certain orbit can be easily modified without changing the theory's coherence.
[3] Popper argued that scientific hypotheses should be subjected to methodological testing to select for the strongest hypothesis.