Postgres psqlのタイムゾーンを設定するにはどうすればよいですか？

psql (9.1.4)
Type "help" for help.

richardh=> show timezone;
 TimeZone 
----------
 GB
(1 row)

richardh=> set timezone='UTC';
SET
richardh=> show timezone;
 TimeZone 
----------
 UTC
(1 row)

richardh=> set timezone='US/Eastern';
SET
richardh=> show timezone;
  TimeZone  
------------
 US/Eastern
(1 row)

richardh=> set timezone='blah';
ERROR:  invalid value for parameter "TimeZone": "blah"