How is the hour angle defined in celestial navigation?

In celestial navigation, the hour angle is defined as the angle between the observer's meridian and the hour circle of a celestial object. The hour angle represents the time since the object crossed the observer's meridian, expressed in angular measurement. Specifically, it is measured in degrees, where one hour corresponds to 15 degrees of angular movement because the Earth rotates 360 degrees in 24 hours.

This concept is crucial for navigation as it helps determine the position of celestial bodies in relation to an observer on Earth. Understanding the hour angle allows navigators to calculate local time and determine their geographic position based on celestial observations. For example, if a navigator knows the declination of a star and its hour angle, they can find their latitude and longitude, aiding in their navigation efforts.

The other options do not accurately capture the specific definition of the hour angle as it relates to celestial navigation. Instead, they reference other aspects of celestial positioning or measurement that do not directly correlate with the precise understanding of hour angles in this context.