How is the X axis determined?

In direction of the Celestial North Pole

In direction of the Celestial South Pole

In the direction of the Vernal Equinox

In direction of the position of the moon

Correct Answer : In the direction of the Vernal Equinox

Explanation : The Ecliptic Coordinate system defines its X axis in the direction of the Vernal Equinox. Vernal Equinox is the point of intersection of the Celestial Equator and the Ecliptic plane. When Sun is at Vernal Equinox, all Earth locations experience identical durations of daylight and darkness. Position of moon is not used to define axis in the Ecliptic system.

Recently Updated in Spaceflight Mechanics Questions

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.