Coordinated Universal Time (UTC) is the time at the zero or Prime meridian, which runs through Greenwich, England. Time changes one hour with each change of 15 degrees in longitude. The five time zones in the US proper and Canada roughly follow these lines.

Conversion Between UTC and the Pacific Time Zone

Pacific Standard Time is equal to UTC minus 8 hours.
Pacific Daylight Time is equal to UTC minus 7 hours.

• UTC = Coordinated Universal Time

• PDT = Pacific Daylight Time

• PST = Pacific Standard Time

• *0000 and 2400 are interchangeable.
  (2400 is associated with the date of the day ending, 0000 with the day just starting.)

For more information on UTC, see the following sites.

• U.S. National Institute of Standards and Technology FAQ page on Time.

• U.S. Naval Observatory's Systems of Time page.

• U.K. Royal Observatory's Time page.

• World Wide Web Consortium (W3C) W3C Specification about UTC Date and Time.

• Wikipedia.