To an astronomer, does it look like Pluto? (3,4)
I believe the answer is:
dog star
'pluto?' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for dog star that I've seen before include "Drags to find other name for Sirius" , "clearly visible shiner" , "What may not be seen on cloudy night" , "'Another name for the Sirius constellation (3,4)'" , "heavenly body?" .)