little information related to survey (field astronomy ) zenith and nadir ,sensible horizon ,equator and seasons and the sky local sidereal time

1. FIELD ASTRONOMY
• A Sphere is a solid bounded by a surface and is such
that every point on the surface is equidistant from a certain
point called the centre of a sphere. It is a solid formed by the
revolution of a circle or a semi-circle about its diameter.
• A radius of a sphere is a straight line joining the centre
to any point on the surface of a sphere.
• A section of a sphere by any plane is a circle.
• A section of a sphere is called a great circle when the
cutting plane passes through the centre of the sphere.
• A section of a sphere is called a small circle when the
plane cutting the surface does not pass through the centre of
the sphere.
• The shortest distance between any two points on the
surface of a sphere is along an arc of a great circle passing
through them

2. FIELD ASTRONOMY

3. FIELD ASTRONOMY
• Nautical Mile: - A nautical mile is the distance
measured along the great circle joining two points which
subtend one minute of arc at the centre of the earth. Taking
the radius of the earth to be equal to 3960 miles, we have
= circumference of the great circle
3600
x 60
= 2π x 3960 x 5280 = 6080 feet
3600
x 60
= 1855.109 m.
The distance between two points in nautical miles
measured along the parallel of latitude is called the departure.

4. FIELD ASTRONOMY
• Astronomical Terms: -
• The Celestial Sphere is
an imaginary sphere upon the
surface of which all the stars in
the sky appear to be studded to
an observer stationed at its
centre.

5. FIELD ASTRONOMY
• The Zenith (Z) is the intersection of a vertical line through
the observer’s station with the upper portion of the celestial
sphere. It is the point on the celestial sphere immediately above
the observer’s station.
• The Nadir is the intersection of a vertical line through the
observer’s station with the lower portion of the celestial sphere.
It is the point on the celestial sphere vertically below the
observer’s station.
• The Celestial Horizon (also
called True or Rational
Horizon) is the great circle in
which a plane at right angles
to the Zenith and Nadir line
and passing through the
centre of

6. FIELD ASTRONOMY
the earth intersects the celestial sphere. The Zenith and Nadir
are the poles of the celestial horizon.
• The Sensible Horizon is the circle in which a plane
tangent to the earth’s surface (or at right angles to the Zenith
and Nadir line) and passing through the point of observation
intersects the celestial sphere. The line of sight of an
accurately levelled telescope lies in this plane.
• The Visible Horizon is the circle of contact of the earth
and the cone of visual rays passing through the point of
observation.
• The Terrestrial Equator (or simply, Equator) is the
great circle of the earth, the plane of which is perpendicular to
the axis of rotation (polar axis).

7. FIELD ASTRONOMY
• The Polar Axis (or Polar Diameter) is the diameter
about which the earth spins. The extremities of the axis of
rotation (polar axis) of the earth, are known as the Poles. They
are distinguished as the North Pole and the South Pole.
• The Celestial Equator is the great circle in which the
plane of the equator cuts the celestial sphere.
• The Celestial Poles are the points of intersection of
the axis of the earth (or the polar axis) when produced with
the celestial sphere.
• The Ecliptic is the great circle which the sun appears
to trace on the celestial sphere with the earth as a centre in
the course of a year.
• The Celestial Meridian is the great circle in which the
plane passing through the celestial poles intersects the
celestial sphere.

8. FIELD ASTRONOMY
• The Meridian of a place or an observer is the great
circle passing through the zenith, and nadir and poles.
• The Vertical Circle is the great circle passing through
the zenith and nadir. The meridian of a place is, therefore,
also a vertical circle.
• The Prime Vertical is the vertical circle which passes
through the east and west points of the horizon. It is at right
angles to the meridian of the place.
• The Latitude (θ) of a place or station is the angular
distance measured from the equator towards the nearer pole,
along the meridian of the place. The latitude is the declination
of the zenith.
• The Co-latitude of a place is the angular distance from
the zenith to the pole. It is the complement of the latitude, and
is, therefore, equal to 900
- latitude.

9. FIELD ASTRONOMY
• The Longitude (Ø) of a place is the angular measure
of the arc of the equator between some primary meridian and
the meridian of the place.
• The Altitude ( ) of a heavenly body is its angular
distance above the horizon, measured on the vertical circle
passing through the body.
• The Co-altitude, also called the Zenith distance (z), is
the angular distance of a heavenly body from the zenith. It is
the complement of the altitude and equals 900
- altitude.
• The Azimuth (A) of a heavenly body is the angle
between the observer’s meridian and the vertical circle
passing through the body from north celestial pole.
• The Declination (δ) of a heavenly body
is its angular distance from the equator, measured
along the meridian called the declination

10. FIELD ASTRONOMY
the great circle passing through the body and the celestial
poles.
• The Co-declination, also termed as the Polar Distance
(p), is the angular distance of the heavenly body from the
pole. It is the complement of the declination, and is equal to
900
- declination.
• The Hour Angle (H) of a heavenly body is the angle
between the observer’s meridian and the declination circle
passing through the body.
• The Right Ascension (R.A.) of a heavenly body is its
equatorial angular distance measured eastward from the First
Point of Aries.

11. FIELD ASTRONOMY

12. FIELD ASTRONOMY
• Local Sidereal Time (LST): The hour angle of the vernal
equinox or, equivalently, the right ascension of points on the
celestial meridian. LST is dependent upon the observer's
position and is constantly changing with time.
• North point: The point that is on the horizon and directly
North
• Solstice: Time of greatest or smallest declination for the
Sun.
• Equinox: Time when the Sun crosses the celestial equator.
(Vernal = spring)

13. FIELD ASTRONOMY
Seasons and the Sky
•Vernal Equinox - first day of spring; the Sun lies exactly over
the equator and is passing into the N. hemisphere
•Autumnal Equinox - first day of autumn; the Sun lies exactly
over the equator and is passing into the S. hemisphere
•Summer Solstice - first day of summer; the Sun is highest in
the sky for N. observers (lowest for S. observers)
•Winter Solstice - first day of winter; the Sun is lowest in the
sky for N. observers (highest for S. observers)

14. FIELD ASTRONOMY