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Friday, April 1, 2011

AZIMUTH BY THE EX-MERIDIAN OBSERVATION ON THE SUN


AZIMUTH BY THE EX-MERIDIAN OBSERVATION ON THE SUN

Aim :
            To find the angle between the observes meridian and the vertical circle through the body.

General :
            The required altitude and the horizontal angles are those to the sun’s centre. Hence the hairs should be set tangential to the two limbs simultaneously. The opposite limbs are then observed by changing the face as shown in figure.

Procedure :
1.      Set the instrument over the station mark and leveling very accurately.
2.      Clamp both the plates to zero and sight the reference mark (RM).
3.      Turn to the sun and observe and altitude and horizontal angle with the sun in quadrant 1 of the cross hair system.
The motion in the azimuth is slow and the vertical hair is kept in contact by the upper tangent screw, the sun being allowed to make contact with the horizontal hair the line of observation is also noted.
4.      Using two tangential screw as quickly as possible, bring the sun in to the quadrant 3 of the cross hairs and again read the horizontal and vertical angles. Observe also the chronometer time.
5.      Turn the RM. Reverse the face and take another side to RM.
6.      Take two more observations of the sun precisely in the same way as in steps 3 and 4 above, but this time with the sun is quadrant 2 and 4. Note the time of each observations.
7.      Finally bisect the RM to see that the reading is zero.
During the above four observations (two with face left and two with face right)

Result :
            Azimuth of the given line =

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