B.tech Civil Semester-IV, Surveying-II

B.
tech Civil Semester-IV, Surveying-II
Presentation by: A J Gondaliya

 The study of astronomy is required in surveying for the
determination of the absolute location of a point or the
absolute location and direction of any line on the surface of
the earth.
 Absolute location of any point is found in terms of the

longitude and latitude.
 Absolute direction of a line is defined, by the angle which
the line makes with the true meridian in terms of the true
bearing or azimuth.
 The azimuth of a line is determined by making angular

observation on some celestial body, such as the sun or the
Polaris (north star).
 In a clear night, the sky appears as
a vast hollow hemisphere with its
interior studded with innumerable
stars.
 On observing the sky for some
duration it appears that the
celestial bodies are revolving
around the earth with its centre at
the position of the observer.
 The stars move in a regular manner and maintain same
position relative to each other.
 Consequently, terrestrial position or direction defined with

reference to celestial body remains absolute for all practical
purposes in plane surveying. Thus, the absolute direction of a
line can be determined from the position/direction of a
celestial body.
 Celestial sphere : An imaginary sphere of infinite radius with
the earth at its centre and other celestial bodies studded on
its inside surface is known as celestial sphere.
 Great Circle (G.C) : The imaginary line of intersection of an

infinite plane, passing through the centre of the earth and
the circumference of the celestial sphere is known as great
circle.
 Zenith (Z) : If a plumb line through an observer is extended
upward, the imaginary point at which it appears to intersect
the celestial sphere is known as Zenith. The imaginary point
at which it appears to intersect downward in the celestial
sphere is known as Nadir (N).
 Vertical circle : Great circle passing through zenith and nadir

is known as vertical circle.
 Poles : If the axis of rotation of the earth is imagined to be
extended infinitely in both directions, the points at which it
meets the celestial sphere are known as poles.
 The point of intersection in the northern hemisphere is

known as north celestial pole and that in the southern
hemisphere as south celestial pole.
 Equator : The line of intersection of an infinite plane passing
through the centre of the earth and perpendicular to the line
joining celestial poles with the celestial sphere.
 Hour circle : Great circle passing through celestial poles is

known as hour circle, also known as declination circle.
 Meridian : The hour circle passing through observer's zenith

and nadir is known as (observer's) meridian. It represents the
North-South direction at observer station.
 Altitude (h) : The altitude of a celestial body is the angular
distance measured along a vertical circle passing through the
body. It is considered positive if the angle measured is above
horizon and below horizon, it is considered as negative.
 Azimuth (A) : The azimuth of a celestial body is the angular

distance measured along the horizon from the observer's
meridian to the foot of the vertical circle passing through the
celestial body
 Declination (δ): The declination of a celestial body is the angular
distance measured from the equator to the celestial body along
the arc of an hour circle. It is considered positive in North direction
and negative in South.
 Ecliptic: The great circle along which the sun appears to move
round the earth in a year is called the ecliptic.
 Prime meridian: Reference meridian that passes through the Royal

Naval Observatory in Greenwich, England is known as prime
meridian; it is also known as Greenwich meridian.
 Longitude (λ) : The longitude of an observer's station is the
angular distance measured along the equator from the prime
meridian to the observer's meridian. It varies from zero
degrees to 180° E and 0° to 180° W.
 Latitude (Ø): The latitude of an observer's station is the

angular distance measured along the observer's meridian
from the equator to the zenith point. It varies from zero
degree to 90° N and 0° to 90° S.
 The spherical triangle formed by arcs of observer's meridian,
vertical circle as well as hour circle through the same celestial
body is known as an astronomical triangle.
 The vertices of an astronomical triangle are Zenith point (Z),

celestial pole (P) and the celestial body (S) and thus termed
as ZPS triangle.
 The spherical triangle formed
by arcs of observer's meridian,
vertical circle as well as hour
circle through the same
celestial body is known as an
astronomical triangle.
 The vertices of an astronomical triangle are Zenith point (Z),
celestial pole (P) and the celestial body (S) and thus termed
as ZPS triangle.
 Polar distance (PS or p) : The angular distance from the

celestial pole (P) to the celestial body (S) along the hour
circle is known as polar distance. It is also known as co-
declination and is designated by p (= 90°- δ), where d is the
declination of the celestial body, S.
Zenith distance (ZS or z) :
Angular distance from observer's
zenith (Z) to the celestial body (S)
along the vertical circle is known
as zenith distance. It is also known
as co-altitude and is designated by
z (= 90°- h), where h is the altitude
of the celestial body, S.

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B.

tech Civil Semester-IV, Surveying-II

Presentation by: A J Gondaliya

 Absolute location of any point is found in terms of the

 The azimuth of a line is determined by making angular

 Consequently, terrestrial position or direction defined with

 Great Circle (G.C) : The imaginary line of intersection of an

 Vertical circle : Great circle passing through zenith and nadir

 The point of intersection in the northern hemisphere is

 Hour circle : Great circle passing through celestial poles is

 Meridian : The hour circle passing through observer's zenith

 Azimuth (A) : The azimuth of a celestial body is the angular

 Prime meridian: Reference meridian that passes through the Royal

 Latitude (Ø): The latitude of an observer's station is the

 The vertices of an astronomical triangle are Zenith point (Z),

 Polar distance (PS or p) : The angular distance from the

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