The sources of error in transit work are:-
- Instrumental
- Personal
- Natural
1. Instrumental Error:-
The totalinstrumental error to an observation may be due solely to one or to a combination of these. The following are errors due to imperfect adjustment of the instrument.
i. Error due to imperfect adjustment of plate levels:
If the upper and lower plates are not horizontal when the bubbles in plate levels are centered, the vertical axis of the instrument will not be truly vertical. Ther horizontal angles will be measured in an inclined plane and not in a horizontal plane. The vertical angles measured will also be incorrect.
ii. Error due to line of collimation not being . perpendicular to the horizontal axis:-
iii. Error due to horizontal axis not being perpendicular to the vertical axis:-
iv. Error due to non- parallelism of the axis of telescope level and line of collimation:-
v. Error due to imperfect adjustment of the vertical circle vernier:-
vi. Error due to eccentricity of inner and outer axis:-
vii. Error due to imperfect graduation:-
viii. Error due to eccentricity of verniers:-
2. Personal Error:-
(a). Errors in manipulation:-
i. Inaccurate centering:-
ii. Inaccurate levelling:-
iii. Slip:-
iv. Manipulation wrong tangent screw:-
(b). Errors in sighting and reading:-
i. Inaccurate bisection of points observed:-
ii. Parallax:-
iii. Mistakes:-
3. Natural Errors:-
- Unequal atmospheric refraction due to high temperature.
- Unequal expansion of parts of telescope and circles due to temperature change.
- Unequal settlement of tripod.
- Wind producing vibrations.
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