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TERRESTRIAL AND COASTAL NAVIGATION

EARTH TERMS AND DEFINITION

  • This section covers key definitions and terms related to Earth navigation as part of the course objectives for DNS Semester 1 / TCN I /2021/ MMH with a focus on shaping future maritime leaders.

LEARNING OUTCOMES

  • At the end of the lesson, students will be able to:
    • Understand the Shape of the Earth.
    • Differentiate between Great Circle and Small Circle.
    • Distinguish between Geographical Pole and Magnetic Pole.
    • Define the following key terms:
    • Meridian
    • Prime Meridian
    • Equator
    • Latitude
    • Longitude
    • D’lat (Differential Latitude)
    • D’long (Differential Longitude)

SHAPE OF THE EARTH

  • The Earth is not a perfect sphere.
  • It has a true shape classified as an oblate spheroid or ellipsoid.
  • For calculation purposes, the Earth is often approximated as a sphere, with negligible errors associated with this assumption.

GREAT CIRCLE FACTS

  • A Great Circle is defined by several important characteristics:
    1. Definition:
    • A Great Circle is a circle drawn on the surface of the Earth whose plane passes through the center of the Earth.
    1. Division:
    • It divides the Earth into two equal parts.
    1. Size:
    • It is the largest circle that can be drawn on the Earth.
    1. Shortest Distance:
    • The shortest distance between two points on the Earth's surface lies along the Great Circle arc. The shorter arc on the Great Circle represents the shortest distance between those two points.
    1. Uniqueness:
    • For any two given points on the Earth, only one Great Circle can be drawn through those points, except in cases where the two points are 180° apart (on opposite sides), where an infinite number of Great Circles can be drawn.

SMALL CIRCLE

  • A Small Circle is defined as:
    • Any circle drawn on the surface of the Earth whose plane does not pass through the Earth's center.

SPHERICAL TRIANGLE

  • A spherical triangle consists of three sides formed by the arcs of Great Circles that intersect each other.

POLES OF A GREAT CIRCLE

  • If a line is extended from the center of the Great Circle, perpendicular to the plane of the Great Circle, it intersects the sphere at two points 180° apart. These points are referred to as the poles of the Great Circle.

EARTH'S POLES

  • Earth has two main types of poles:
    • Geographical Poles
    • Magnetic Poles
GEOGRAPHICAL POLES
  • The geographical poles (North Pole and South Pole) are points where the Earth's rotational axis intersects its surface.

GREAT CIRCLE AND SMALL CIRCLE USAGE

  • The distinctions between Great Circles and Small Circles are useful for navigation:
    • Parallel of Latitude: This is a Small Circle on the Earth's surface.
    • Equator: This represents a Great Circle on the Earth's surface.
    • Meridian: A semi-Great Circle.

THE EQUATOR

  • The Equator is defined as:
    • A Great Circle on the Earth's surface whose plane is perpendicular to the Earth's rotational axis.

LATITUDE

  • Latitude is defined in two ways:
    1. As the arc on the meridian between the Equator and a given parallel of latitude, measured in degrees and minutes (e.g., 100° 20’ N).
    2. As the angle at the Earth's center measured vertically from the Equator to the point in question, named either North or South.
  • Maximum Latitude values can reach 90° N/S.

PARALLEL OF LATITUDE

  • A Parallel of Latitude is a Small Circle on the Earth's surface, defined by being parallel to the Equator and intersecting the Earth's rotational axis at 90°.
  • All points on the same parallel of latitude have the same latitude value and name.

MERIDIAN

  • A Meridian is a semi-Great Circle that runs between the two geographical poles.
  • All meridians intersect the Equator at 90°.

PRIME MERIDIAN

  • The Prime Meridian is a specific meridian that passes through an arbitrary point in Greenwich.
  • It serves as the reference point for measuring longitude, with a value of 0° longitude (East or West).

LONGITUDE

  • Longitude can be defined in two principal ways:
    1. As an arc on the Equator measured from the Prime Meridian to the meridian of a given point, with designations East or West (e.g., Longitude 120° 15.6’ E).
    2. As the angle at the center of the Earth, measured horizontally from the Prime Meridian to the meridian of the point in question.
  • Maximum Longitude values are 180° E or W from the Prime Meridian.

EXAMPLES AND APPLICATIONS

  • Exercise Example for Positioning: For a point such as Mt. Lily with coordinates Lat 30° N, Long 060° E,
    • A sketch should illustrate:
    • Geographical Pole
    • Equator
    • Prime Meridian
    • Observer Meridians
    • Parallel of Latitude
    • Latitude
    • Longitude
    • Vessel Position

SIDE AND TOP VIEW OF EARTH

  • Side and Top view illustrations would provide a more visual understanding of the Earth’s navigation points relative to the mentioned coordinates.

END OF PRESENTATION

  • Thank you for this overview of Terrestrial and Coastal Navigation. The study of these principles equips students with essential knowledge for maritime leadership.