Which point is considered as the origin for the Ecliptic Coordinate system?

Center of the Sun

Center of the Earth

Celestial South Pole

Celestial North Pole

Correct Answer : Center of the Sun

Explanation : The Ecliptic Coordinate system takes the center of the Sun as the origin. For the ECI system, the Earth’s center is considered as the origin. Celestial North Pole and Celestial South Pole are not taken as the point of origin in the coordinate systems.

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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.