All astronomers are amateurs. When it comes to the heavens, there's only one professional.
5 seconds sound clip from the The Wolf Man (1941) movie soundboard.
You can hear this line at 00:05:52.120 in the Blu-ray version of the movie.
Quote context
[...]
- It's excellent! Where'd you learn such precision work?
- Optical company in California. We did quite a job on that Mount Wilson Observatory.
- Are you interested in astronomy?
- All astronomers are amateurs. When it comes to the heavens, there's only one professional.
- Fine. Well, I've got some things to do before lunch. I'll leave you to it.
- Well, good afternoon, sir. May I help you?
- I'm looking for a gift. Something in earrings.
- Certainly. We have some very nice ones.
- There's these diamond ones. They're very smart. Or how about these pearl ones?
[...]