Which of the following is the correct representation of Altitude?

0 hour = Celestial Horizon

0� = Celestial Horizon

-90� = Zenith

+90� = Nadir

Correct Answer : 0� = Celestial Horizon

Explanation : 0° Altitude represents the Celestial Horizon as the vertical distance from the horizon is zero. The angular distance is measured in degrees and not in hours. Above the horizon is considered as positive sign & below the horizon is considered as negative sign. So the Zenith can be represented as +90° whereas the Nadir is represented as -90° altitude.

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How many rotations are required to transform the ECI coordinate system to the perifocal system?

Correct Answer : Option (D) : 3

Explanation : The coordinate transformation from XYZ frame to X’Y’Z’ frame is carried out by a single rotation about one axis. The other two axes remain in the same plane. But to transform from the ECI coordinate system to the perifocal system, there have to be successive 3 rotations. The first rotation is about Z axis, second is through X’ axis and the final rotation is bout Z’’ axis.