Pick up the correct statement from the following: A. Refraction correction is zero when the celestial body is in the zenith B. Refraction correction is 33′ when the celestial body is on the horizon C. Refraction correction of celestial bodies depends upon their altitudes D. All the above

The correct answer is D. All the above.

Refraction is the bending of light as it passes from one medium to another. When light travels from the Earth’s atmosphere to space, it is refracted by the atmosphere. This refraction causes celestial bodies to appear higher in the sky than they actually are. The amount of refraction depends on the angle of the celestial body above the horizon. When a celestial body is on the horizon, the angle of refraction is 33′. As the celestial body rises in the sky, the angle of refraction decreases. When a celestial body is at the zenith, the angle of refraction is zero.

The amount of refraction also depends on the temperature and pressure of the atmosphere. When the atmosphere is warm and humid, the refraction is greater than when the atmosphere is cold and dry.

Refraction is an important factor to consider when observing celestial bodies. It can cause errors in measurements of the altitude and position of celestial bodies.