simple transaction question

I want to archive rows from the sys.aud$ table into a table called aud$hist. Step 1 is to insert all rows from sys.aud$ into aud$hist. Step 2 is to delete the same rows from sys.aud$. Sounds simple enough. the script looks like this:

insert into aud$hist (select * from sys.aud$); delete from sys.aud$;
commit;

The problem is that in between steps 1 and 2, new rows are being added to the sys.aud$ table by someone else logging in and those rows get deleted without ever being copied. How can this happen in a transaction oriented RDBMS? I thought that once my transaction began, it would see the exact same view of the database regardless of any other simultaneous transactions occurring on the system, until I either committed or rolled back. Obviously that's not happening. What can I do to get Oracle to act the way I think it should?

--
Chuck Hamilton
Sr. DBA
Keystone Mercy Health Plan
chuckh_at_dvol.com

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