Didot  Suggested by jerseygirl 
Baskerville  Suggested by flawlessaniston 

http://www.dafont.com/forum/read/142658/christopher-nolan-s-interstellar-logo-font

thanks!!

oh no thats not the same. . and its not free .. can someone list a free one please?

Yes, the font indeed appears to be Didot, look again:
http://myfonts.us/td-12GkIb


Not identical, but free and maybe close enough:

http://www.fontsquirrel.com/fonts/theano-didot

The closest font I could find was Baskerville which is probably already pre-installed in your computer!

thank you ya'll are the best!!