Help with WHERE & Date clause

Hi, it's me again :D
*some might know me lol*

I am doing another query which works fine
but it does not accept the YEAR '2013' format

WHERE YR_VIEWING.DATEVIEWED = '2013';

Basically, I am making a query to show all data based on the DateViewed 2013. Now the Viewing table has the following data:

DateViewed DATE,

Is the normal format of DATE as yyyy-mm-dd or rather dd-mm-yyyy ???
Do I have to change to : DateViewed TO_DATE('DD-Mon-YYY') in order for the upcoming data to be displayed as 01-May-2013 ??


By the way, the imported dates into the Viewing table show as in the following format: 12-Jan-13


I also tried with ='13' but does not seem to work