Celestial Navigation (CN)
CN - CELESTIAL NAVIGATION | EXAM QUESTIONS AND
CORRECT ANSWERS | VERIFIED MARITIME CELESTIAL
NAVIGATION LATEST 2026/2027
CELESTIAL NAVIGATION (CN)
1. The celestial sphere used in navigation is best described as:
A. A physical shell of stars at a fixed distance from the Sun
B. The sphere traced by the Moon's orbit around the Earth
C. A sphere of radius equal to one astronomical unit centred on the Sun
D. An imaginary sphere of infinite radius centred on the Earth, onto which all
celestial bodies are projected
ANSWER : D. An imaginary sphere of infinite radius centred on the
Earth, onto which all celestial bodies are projected
Navigators treat every body as lying on one imaginary sphere centred on the
Earth; actual distances are ignored for the geometry.
2. The celestial equator is:
A. The great circle passing through the observer's zenith and the poles
B. The apparent annual path of the Sun among the stars
C. The small circle marking the limit of the Moon's declination
D. The projection of the Earth's equator onto the celestial sphere
ANSWER : D. The projection of the Earth's equator onto the celestial
sphere
Extending the plane of the terrestrial equator outward gives the celestial
equator, the reference for declination.
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, Celestial Navigation (CN)
3. Declination on the celestial sphere corresponds most closely to which
terrestrial coordinate?
A. Departure
B. Difference of longitude
C. Longitude
D. Latitude
ANSWER : D. Latitude
Declination is the angular distance north or south of the celestial equator, just as
latitude is measured from the Earth's equator.
4. Greenwich Hour Angle (GHA) is measured:
A. Eastward or westward from Greenwich through 180°
B. Northward from the celestial equator through 90°
C. Eastward from the first point of Aries through 360°
D. Westward from the Greenwich celestial meridian through 360°
ANSWER : D. Westward from the Greenwich celestial meridian through
360°
GHA always runs westward from the upper branch of the Greenwich meridian,
from 0° to 360°.
5. Sidereal Hour Angle (SHA) of a star is measured:
A. Eastward from the Greenwich meridian
B. Westward from the hour circle of the first point of Aries
C. Westward from the observer's meridian
D. Eastward from the hour circle of the Sun
ANSWER : B. Westward from the hour circle of the first point of Aries
SHA is the westward angle from Aries to the star's hour circle; it changes very
slowly, so it is tabulated for several days at once.
6. The GHA of a star is found by:
A. Adding the star's declination to its SHA
B. Subtracting the star's SHA from the GHA of Aries
C. Adding the star's SHA to the GHA of Aries
D. Subtracting the observer's longitude from the star's SHA
ANSWER : C. Adding the star's SHA to the GHA of Aries
GHA star = GHA Aries + SHA star, removing 360° when the total exceeds
360°.
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, Celestial Navigation (CN)
7. Local Hour Angle (LHA) is obtained from GHA by:
A. Adding west longitude or subtracting east longitude
B. Adding the declination
C. Subtracting the SHA
D. Adding east longitude or subtracting west longitude
ANSWER : D. Adding east longitude or subtracting west longitude
The standard memory aid is 'longitude east, add; longitude west, subtract' when
going from GHA to LHA.
8. The geographical position (GP) of a celestial body is:
A. The observer's position at the moment of the sight
B. The point on the Earth's surface directly beneath the body
C. The point on the celestial equator directly below the body
D. The point where the body crosses the observer's horizon
ANSWER : B. The point on the Earth's surface directly beneath the body
At the GP the body would be seen exactly in the zenith; its latitude equals the
declination and its longitude relates to GHA.
9. The point on the celestial sphere directly above the observer is the:
A. Zenith
B. Elevated pole
C. Nadir
D. Prime vertical
ANSWER : A. Zenith
The zenith lies vertically overhead, 90° from every point on the celestial
horizon.
10. The nadir is:
A. The point where the ecliptic crosses the celestial equator
B. The depressed celestial pole
C. The point on the celestial sphere directly beneath the observer
D. The lowest altitude reached by a circumpolar star
ANSWER : C. The point on the celestial sphere directly beneath the
observer
The nadir is diametrically opposite the zenith.
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, Celestial Navigation (CN)
11. The celestial horizon is a great circle located:
A. At the observer's height of eye below the visible horizon
B. 23°26' from the celestial equator
C. 90° from the observer's zenith
D. Along the observer's celestial meridian
ANSWER : C. 90° from the observer's zenith
Altitude is measured from the celestial horizon, the great circle everywhere 90°
from the zenith.
12. Zenith distance of a body is equal to:
A. 90° minus the observed altitude
B. 90° minus the declination
C. The latitude minus the declination in all cases
D. The observed altitude plus the dip
ANSWER : A. 90° minus the observed altitude
Zenith distance is the complement of altitude, the arc from the zenith down to
the body.
13. The radius of a circle of equal altitude on the Earth's surface, in nautical
miles, equals:
A. The observed altitude expressed in minutes of arc
B. The polar distance expressed in degrees
C. The declination expressed in minutes of arc
D. The zenith distance expressed in minutes of arc
ANSWER : D. The zenith distance expressed in minutes of arc
Each minute of arc on a great circle is one nautical mile, so a zenith distance of
30° gives a radius of 1,800 nm around the GP.
14. The three vertices of the astronomical (navigational) triangle are:
A. The GP, the dead reckoning position and the assumed position
B. The zenith, the nadir and the first point of Aries
C. The elevated pole, the observer's zenith and the celestial body
D. The Sun, the Moon and the observer
ANSWER : C. The elevated pole, the observer's zenith and the celestial
body
Solving this spherical triangle gives computed altitude and azimuth for sight
reduction.
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CN - CELESTIAL NAVIGATION | EXAM QUESTIONS AND
CORRECT ANSWERS | VERIFIED MARITIME CELESTIAL
NAVIGATION LATEST 2026/2027
CELESTIAL NAVIGATION (CN)
1. The celestial sphere used in navigation is best described as:
A. A physical shell of stars at a fixed distance from the Sun
B. The sphere traced by the Moon's orbit around the Earth
C. A sphere of radius equal to one astronomical unit centred on the Sun
D. An imaginary sphere of infinite radius centred on the Earth, onto which all
celestial bodies are projected
ANSWER : D. An imaginary sphere of infinite radius centred on the
Earth, onto which all celestial bodies are projected
Navigators treat every body as lying on one imaginary sphere centred on the
Earth; actual distances are ignored for the geometry.
2. The celestial equator is:
A. The great circle passing through the observer's zenith and the poles
B. The apparent annual path of the Sun among the stars
C. The small circle marking the limit of the Moon's declination
D. The projection of the Earth's equator onto the celestial sphere
ANSWER : D. The projection of the Earth's equator onto the celestial
sphere
Extending the plane of the terrestrial equator outward gives the celestial
equator, the reference for declination.
Page 1 of 51
, Celestial Navigation (CN)
3. Declination on the celestial sphere corresponds most closely to which
terrestrial coordinate?
A. Departure
B. Difference of longitude
C. Longitude
D. Latitude
ANSWER : D. Latitude
Declination is the angular distance north or south of the celestial equator, just as
latitude is measured from the Earth's equator.
4. Greenwich Hour Angle (GHA) is measured:
A. Eastward or westward from Greenwich through 180°
B. Northward from the celestial equator through 90°
C. Eastward from the first point of Aries through 360°
D. Westward from the Greenwich celestial meridian through 360°
ANSWER : D. Westward from the Greenwich celestial meridian through
360°
GHA always runs westward from the upper branch of the Greenwich meridian,
from 0° to 360°.
5. Sidereal Hour Angle (SHA) of a star is measured:
A. Eastward from the Greenwich meridian
B. Westward from the hour circle of the first point of Aries
C. Westward from the observer's meridian
D. Eastward from the hour circle of the Sun
ANSWER : B. Westward from the hour circle of the first point of Aries
SHA is the westward angle from Aries to the star's hour circle; it changes very
slowly, so it is tabulated for several days at once.
6. The GHA of a star is found by:
A. Adding the star's declination to its SHA
B. Subtracting the star's SHA from the GHA of Aries
C. Adding the star's SHA to the GHA of Aries
D. Subtracting the observer's longitude from the star's SHA
ANSWER : C. Adding the star's SHA to the GHA of Aries
GHA star = GHA Aries + SHA star, removing 360° when the total exceeds
360°.
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, Celestial Navigation (CN)
7. Local Hour Angle (LHA) is obtained from GHA by:
A. Adding west longitude or subtracting east longitude
B. Adding the declination
C. Subtracting the SHA
D. Adding east longitude or subtracting west longitude
ANSWER : D. Adding east longitude or subtracting west longitude
The standard memory aid is 'longitude east, add; longitude west, subtract' when
going from GHA to LHA.
8. The geographical position (GP) of a celestial body is:
A. The observer's position at the moment of the sight
B. The point on the Earth's surface directly beneath the body
C. The point on the celestial equator directly below the body
D. The point where the body crosses the observer's horizon
ANSWER : B. The point on the Earth's surface directly beneath the body
At the GP the body would be seen exactly in the zenith; its latitude equals the
declination and its longitude relates to GHA.
9. The point on the celestial sphere directly above the observer is the:
A. Zenith
B. Elevated pole
C. Nadir
D. Prime vertical
ANSWER : A. Zenith
The zenith lies vertically overhead, 90° from every point on the celestial
horizon.
10. The nadir is:
A. The point where the ecliptic crosses the celestial equator
B. The depressed celestial pole
C. The point on the celestial sphere directly beneath the observer
D. The lowest altitude reached by a circumpolar star
ANSWER : C. The point on the celestial sphere directly beneath the
observer
The nadir is diametrically opposite the zenith.
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, Celestial Navigation (CN)
11. The celestial horizon is a great circle located:
A. At the observer's height of eye below the visible horizon
B. 23°26' from the celestial equator
C. 90° from the observer's zenith
D. Along the observer's celestial meridian
ANSWER : C. 90° from the observer's zenith
Altitude is measured from the celestial horizon, the great circle everywhere 90°
from the zenith.
12. Zenith distance of a body is equal to:
A. 90° minus the observed altitude
B. 90° minus the declination
C. The latitude minus the declination in all cases
D. The observed altitude plus the dip
ANSWER : A. 90° minus the observed altitude
Zenith distance is the complement of altitude, the arc from the zenith down to
the body.
13. The radius of a circle of equal altitude on the Earth's surface, in nautical
miles, equals:
A. The observed altitude expressed in minutes of arc
B. The polar distance expressed in degrees
C. The declination expressed in minutes of arc
D. The zenith distance expressed in minutes of arc
ANSWER : D. The zenith distance expressed in minutes of arc
Each minute of arc on a great circle is one nautical mile, so a zenith distance of
30° gives a radius of 1,800 nm around the GP.
14. The three vertices of the astronomical (navigational) triangle are:
A. The GP, the dead reckoning position and the assumed position
B. The zenith, the nadir and the first point of Aries
C. The elevated pole, the observer's zenith and the celestial body
D. The Sun, the Moon and the observer
ANSWER : C. The elevated pole, the observer's zenith and the celestial
body
Solving this spherical triangle gives computed altitude and azimuth for sight
reduction.
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