Briefly gentlemen, it is this: The sun is gradually drawing our planet into its orbit. Soon, the gravitational pull will be so strong that Krypton will be unable to withstand the strain.
11 seconds sound clip from Superman (1948) - Superman Comes To Earth (Chapter 1).
You can hear this line at 00:04:15.404 in the Blu-ray version of the episode.
Quote context
[...]
- I demand that Jor-El explain his reason for uttering this fantastic prophecy.
- We're waiting, Jor-El, for you to spin your tale of horror.
- Yes. But we can use our great ability elsewhere.
[...]