Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_16189 ( "Team" text, "Outgoing manager" text, "Manner of departure" text, "Date of vacancy" text, "Replaced by" text, "Date of appointment" text, "Position in table" text )

### Question ###
What is the date of appointment when the date of vacancy is 21 december 2007?

### Accurate SQL ###

SELECT "Date of appointment" FROM table_16189 WHERE "Date of vacancy" = '21 December 2007'