How many bytes does Date datatype occupy in Oracle 9i/10g?

What a simply question - stupid!

What a puzzle it is!

As the result of the function length I performed using the database Oracle 10g installed on my machine, it is 9.

Which one is the correct answer?

Ref:

7: http://www.psoug.org/reference/datatypes.html

8: http://wiki.answers.com/Q/How_many_bytes_does_date_datatype_occupy_in_oracle_9i

7 or 9: http://topic.csdn.net/t/20020905/16/999226.html