Answer & Solution
Answer: Option
B
Solution:
1. Correction for Refraction:
The correction for refraction is always negative because atmospheric refraction bends light downward, making objects appear higher than their actual position.
To get the true reading, this effect must be corrected by subtracting the refraction correction.
2. Correction for Parallax:
The correction for parallax depends on the observer's position and the object's distance.
It can be positive or negative, depending on whether the observed object is in front of or behind the reference point.
Since it is not always positive, this statement is incorrect.
3. Correction for Semi-Diameter:
The correction for semi-diameter is always positive, not negative.
This correction is applied when measuring celestial bodies (e.g., the Sun or Moon) since observations are usually taken at the edge (limb) rather than at the center.
To obtain the true center position, the semi-diameter is added to the observed value.
4. Correction for Dip:
The correction for dip is always negative because an observer at a height sees the horizon at a lower angle than the true horizon.
To correct this effect, the dip correction is subtracted.
Conclusion:
The incorrect statement is Option B: Correction for parallax is always positive, because it can be either positive or negative, depending on the observation conditions.
Option C is incorrect because the correction for semi-diameter is actually positive, not negative.
