Magnetic Declination Formula, Definition, Categories

Magnetic Declination Formula: The angle between magnetic north and true north on a horizontal plane is referred to as magnetic declination. A positive declination occurs when magnetic north is to the east of true north, while a negative declination occurs when it is to the west. Now, let's explore the formula for magnetic declination.

Magnetic Declination Definition

Magnetic declination, on the horizontal plane, denotes the angle formed between magnetic north and true north. This angle is not constant and undergoes changes based on the earth's position and time. We commonly use the Greek letter δ as a symbol for magnetic declination, also known as magnetic variation. The declination is considered positive when magnetic north is east of true north and negative when it is west.

In the field of magnetic navigation, terms like isogonic lines come into play. A constant declination occurs when these lines maintain a consistent value. Additionally, agonic lines, which are zero-length lines parallel to the declination, represent a noteworthy concept in this context.

Magnetic Declination Formula Categories of North

North is categorized into three types:

True North: True north refers to the direction along the Earth's surface that leads to the true North Pole, also known as the topographical North Pole. This is alternatively called geodetic north. It differs from magnetic north, which is the direction indicated by a compass, and grid north, which is the direction along the grid lines.

Grid North: Grid north is the direction along the grid lines on a map or guide projection that points northwards. The deviation of grid north from true north is typically minimal, making this term useful for navigation purposes.

Magnetic North: Magnetic north is the direction to which a compass needle points due to the Earth's magnetic field. The magnetic poles of the Earth are not fixed in relation to its axis, causing the difference between true north and magnetic north to vary from one location to another.

Magnetic Declination Formula Magnetic Dip

Magnetic dip, also known as dip angle or magnetic inclination, is defined as the horizontal component of the Earth's magnetic field lines. Georg Hartmann discovered this phenomenon in 1544 and named it the dip angle.

When the inclination is positive, it signifies that the Earth's magnetic lines are tilting downward in the northern hemisphere. Conversely, a negative inclination indicates that the magnetic lines are oriented upward in the southern hemisphere.

In 1581, Robert Norman devised the dip circle, a tool used to measure the dip angle or magnetic inclination. Two terms associated with magnetic dip are isoclinic lines, which occur when the shape of the magnetic lines at the Earth's surface is comparable, and aclinic lines, which occur when the shape lines are not comparable (indicating zero dips at the locus of focus).

Magnetic Declination Formula

To determine magnetic declination, various methods can be used:

Declination Calculator: Utilize the Declination Calculator, a straightforward tool that computes declination based on magnetic reference field models. Inputting the year, degree, and longitude of a specific location allows the calculator to provide accurate declination values.

Declination Chart: A magnetic declination chart visually represents the magnetic fields worldwide. This chart serves as a handy tool for determining declination, offering a straightforward way to interpret magnetic field variations across different regions. Compass

Method: Magnetic, true, and compass bearings are the three available types of bearings.

The formula for their relationship is expressed as:

T=M+V

M=C+D

T=C+V+D

Where:  T represents True bearing,  M represents Magnetic Bearing,  C represents Compass Bearing, D represents Compass Deviation,  V represents Variation.

The conditions for interpretation are:

V,D>0 → Easterly Variation and Deviation

V,D<0 → Westerly Variation and Deviation

Bearing Formulas

Magnetic and Compass Bearing:

Magnetic Bearing = True Bearing – Variation

Compass Bearing = Magnetic Bearing – Deviation

Magnetic and True Bearing:

Magnetic Bearing = Compass Bearing + Deviation

True Bearing = Magnetic Bearing + Variation

When using a compass to determine the north direction, it's essential to recognize that the needle aligns with the Earth's magnetic north, not the authentic or true north.

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