Couldn't you just say, "While you're mooning the world, Luna, Princess Celestia has the sun on her bum and a fire burning down below."
Meanwhile, if Celestia wants to set something on fire using the sun, I don't think she even needs a magnifying glass.
Answer: Most ponies find raising dragons far too difficult at such a young age, and end up flushing them down the toilet to join the alligators.
There's an entire civilization of rejected, embittered dragons down there. But I'm sure they'll be okay and not rise up against Equestria or anything.
twi: YUP ya wanna buy a book??????? ??
rarity: oh no thank you darrrling. I just thought this was a drink store.
twi: well since your here.......
rarity: well bye dearie!!!
twi: DEAR PRINCESS CELESTIA TODAY I LEARNED THAT SINCE WHEN DO
PEOPLE BUY MY BOOKS AND PONIES ARE ONLY INTERESTED IN DRINKS