Speaking of astronomy...
"Because of the tenth there now are eight," and "When Xena fell, discord rose in her place" might be related as such:
Xena is another name for the dwarf planet Eris (Eris is the goddess of discord). There were originally believed to be 9 planets including Pluto (in our solar system). Eris was found to appear bigger than Pluto, which would have made it the tenth planet. However, the definition of a planet was made/revised due to Eris/Xena, and dwarf planets were coined. Thus, instead of ten planets, we have only eight.
Fun fact: Because it was simply known as Planet X at first, and nomenclature of celestial bodies is dependent on what type of body they are, astronomers named it Xena after the titular character from Xena: Warrior Prrincess