In his 1977 book, the astronomer J. Allen Hynek (who, for what it's worth, became a credulous believer in UFOs-as-aliens) noted that in his work for Project Blue Book, pilots were the *least* reliable occupation when it came to correctly identifying atmospheric or astronomical phenomena: (2/)

Inner bars scale with galaxy mass like outer bars, but are on average 9% the size of outer bars. Intriguingly, there are some galaxies with single bars as small as typical inner bars in galaxies of the same mass; maybe galaxies where an outer bar failed to form? (6/7)

The frequencies of inner bars and nuclear rings are strong, almost identical functions of galaxy stellar mass: practically no galaxies with masses < 10^10 solar masses have inner bars or nuclear rings, while roughly half of those with masses > 10^10.5 do. (3/7)

Examples of double bars and nuclear rings: NGC 3992 (top) has a double bar (gray arrows indicate both bars); NGC 3351 (middle) has a star-forming nuclear ring; NGC 4340 (bottom) has both (the nuclear ring is passive and purely stellar). (2/7)