Directions in space
PHOTO: AP
How are the directions (North, South, East and West) identified on other planets? Are they common for all the planets in the universe?
R. SHANMUGASUNDARAM
Chennai
The directions (North, South, East and West) on the earth are defined with reference to the rotation axis (N-S) and the sense of rotation (W-E, with the direction of the rising Sun being called the East) of the Earth.
On other planets in the Solar system we may choose to follow the system used on Earth or redefine the system of directions for each planet using its rotation axis for reference.
For most planets in the solar system these are similar to that for the earth, but there are exceptions and peculiar cases like Venus whose rotation is retrograde, so the Sun there rises in the West and Uranus’s rotation axis is nearly perpendicular to the plane of its orbit.
The directions are not common for all the planets in the Universe as the rotational properties of the planets could (and are) different. As a matter of general procedure for defining and identifying directions one needs a reference system. We may stick to the reference system of the Earth, if we wish, with no loss of accuracy.
Dr. H.C. BHATT
Dean, Faculty of Sciences
Indian Institute of Astrophysics
Bangalore
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