USCG Celestial Navigation Practice Exam 2025 - Free Celestial Navigation Practice Questions and Study Guide

Question: 1 / 400

What is the longitude of the geographical position of a body whose Greenwich hour angle is 210° 30'?

120°30'W

75°30'E

60°30'N

149°30'E

To find the longitude given a Greenwich hour angle (GHA), it's important to understand the relationship between GHA and longitude. Greenwich hour angle measures the angular distance in degrees westward from the Greenwich Meridian (0° longitude).

In this case, a GHA of 210° 30' indicates how far west the point is from the prime meridian. To convert the GHA to longitude, we subtract the GHA from 360° if the GHA is greater than 180° because the longitudinal degrees measured westward wrap around the 360° mark.

Thus, we would calculate the longitude as follows:

1. Recognize that 210° 30' GHA indicates this point is west of the prime meridian.

2. Since GHA exceeds 180°, we subtract from 360°:

- 360° - 210° 30' = 149° 30' E.

This calculation reveals that the geographical position corresponding to a GHA of 210° 30' aligns with a longitude of 149° 30' East, confirming option D is indeed the correct answer.

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