Question 1701Navigation General

The correct answer is C) 180° longitude. The reference point for the determination of Greenwich Mean Time (GMT) is the passage of the mean sun over the 0° (or 180°) longitude line, which is known as the Prime Meridian or the Greenwich Meridian. GMT is measured from this reference point, and it is the standard time zone used for navigation and timekeeping purposes. The other options are incorrect because: A) the observer's meridian is not the reference point for GMT, B) the First Point of Aries is the reference point for sidereal time, not GMT, and D) 0° longitude is the same as the Prime Meridian, which is the correct reference point.