Which is the incorrect statement regarding the Ecliptic longitude?

It ranges from 0� to 360�

It is constant for a fixed object

It is measured eastward from Vernal equinox

It is the angular distance of the object along the ecliptic plane

Correct Answer : It is constant for a fixed object

Explanation : The Ecliptic longitude is defined as the angular distance of the object along the ecliptic plane. It is measured eastward from Vernal equinox and it ranges from 0° to 360°. Because of precession, the value for a fixed object changes by 50.3 arc-seconds per year.

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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.