What's the difference between abaft and astern?

Abaft

Definition:

• (prep.) Behind; toward the stern from; as, abaft the wheelhouse.
• (adv.) Toward the stern; aft; as, to go abaft.

Example Sentences:

Astern

Definition:

• (adv.) In or at the hinder part of a ship; toward the hinder part, or stern; backward; as, to go astern.
• (adv.) Behind a ship; in the rear.

Example Sentences:

• (1) 8 sternal and 5 asternal ribs were observed in animals of both breeds.