USCG Celestial Navigation Practice Exam

When determining the line of position (LOP) based on the observed altitude (Ho) of a celestial body, it's crucial to understand the relationship between the altitude and the resulting circle around the geographical position (GP) of that body. In celestial navigation, the line of position typically represents a circle where the navigator is located.

When the observed altitude (Ho) exceeds 75 degrees, the resulting position circle becomes very limited in size, and at this altitude, the effects of the earth's curvature are minimal in terms of the position error. Since the idea of plotting an LOP involves drawing a circle around the GP, a higher altitude such as this causes the circumference of this circle to contract and become tight enough that it can be effectively treated as a point.

As a result, this circle demonstrates a high level of confidence in the navigational accuracy of the position since the closer the altitude is to the zenith (the highest point in the sky directly overhead), the smaller and more defined the circle of uncertainty becomes. Thus, for any altitude noticed above this 75-degree threshold, we generally use it to represent the LOP as a circle around the GP of the body, indicating precision in location estimation.

While other values such as 90 degrees

Ask an Examzify Tutor