Astronomical corrections are applied in case of celestial bodies. They generally include corrections for parallax, for refraction, for semi-diameter, for dip of horizon. All se are not applied at once but are applied based on necessity.

At time of manufacturing, index glass is permanently fixed at right angles to plane of instrument. It also doesn?t need a parallel line of sight, as it is already fixed.

When star is at culmination or at state of transition, it will be able to cross observer?s meridian. It makes it obvious that star crosses a meridian twice during its period of revolution.

Sextant is based on principle that when a ray of light is reflected successively from two mirrors, angle between first and last directions of ray is twice angle between planes of two mirrors which can be mamatically represented as ? = ?/2.

The main objective of zenith telescope involves in spectral energy distributions and red shifts over numeral galaxies. This might help in determining supernovae which is at a distant place.

For determining celestial body position, certain co-ordinates are assumed and those are given as horizon system, independent equatorial system, dependent equatorial system, celestial latitude and longitude system.

The altitude of celestial body can be determined by using formula,
Sin ? = sin ? * cosec ?. Where ? = latitude of observer and ? = declination of celestial body. On substitution, we get
Sin ? = sin 21?43? * cosec 24?56?
Sin ? = 0.87
? = 61?16?.

Napier?s rule is used in determination of distance between two points. It also involves in measurement of altitude and hour angle if declination and latitude are known.

Dependent system has two co-ordinates; among m second co-ordinate is independent on observer?s position. And it will have a declination as its circle of reference.

The altitude correction for semi-diameter can be given as summation of index error with semi-diameter mentioned i.e.,
25?46?21?? + 0?26?21?? = 26?12?42??.