Agonic line is the line joining points having declination-
Zero Declination
Agonic Line and Declination Explained
The question asks about the type of declination associated with an agonic line. To understand this, let's first clarify what declination is and then define the agonic line.
Understanding Magnetic Declination
Magnetic declination is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole). This angle varies depending on your location on Earth and changes over time.
- The Earth's magnetic North Pole is not exactly at the same location as the geographic North Pole.
- Therefore, a compass typically points to magnetic north, not true north.
- To navigate accurately or survey land, it's essential to know the magnetic declination for a specific area.
- If magnetic declination is east, it means magnetic north is east of true north. If it's west, magnetic north is west of true north.
Defining the Agonic Line
An agonic line is a specific type of isoline, which is a line on a map or chart that connects points where a certain value is constant. In the context of geomagnetism, an agonic line connects all points on the Earth's surface where the magnetic declination is zero declination. This means that at any point along an agonic line, magnetic north and true north are perfectly aligned.
- When you are on an agonic line, your compass will point directly to true north (geographic north) without needing any correction for magnetic declination.
- These lines are not fixed; they slowly shift over time due to changes in the Earth's magnetic field.
Comparing Agonic and Isogonic Lines
While an agonic line connects points of zero declination, an isogonic line connects points of the same, non-zero magnetic declination. For example, an isogonic line might connect all points where the declination is 5° East or 10° West.
| Line Type | Characteristic Declination |
|---|---|
| Agonic Line | Zero Declination |
| Isogonic Line | Same (Constant) Declination (can be zero, but typically non-zero) |
Based on the definition, an agonic line specifically refers to the line joining points having zero declination. Therefore, the correct option is the one stating zero declination.
Important Questions from Compass Surveying and Theodolite
Which of the following statement is CORRECT for whole circle bearing?
Least count of a theodolite is ________
The meridians that are parallel to the directions taken by freely moving magnetized needles, as in a compass are called as:
For measurement of vertical angles through theodolite, the instrument should be levelled with reference to the ________ bubble and the ________ clamp that is used to rotate the telescope in the vertical plane.
The following statements given pertain to theodolite used in surveying. Identify the incorrect statement
