Sunday, July 4, 2021

Orienting on Mars

On Earth we all know that the north celestial pole is indicated by the Polar Star. This happens given that the Polaris is almost aligned with the Earth's rotation axis, inclined by just over 23°  respect to the perpendicular to the plane of the ecliptic.

This alignment is only fortuitous: in the southern hemisphere, for example, there is no bright star indicating the south celestial pole.

Following this reasoning, we could therefore think of identifying polar stars also on all the other bodies of the Solar System.

For example, suppose we are on the surface of Mars and look at the sky. The stars we see are exactly the same as those of the terrestrial skies. The only thing different from our planet is the inclination of the rotation axis: the obliquity of the Martian one is in fact about 25°.

In the Northern Hemisphere, the rotation axis points to a region where bright stars are absent. However, this direction is located about halfway between Deneb and Alderamin, respectively the brightest stars of the constellations Cygnus and Cepheus. This alignment could therefore be used to identify the north.

In the southern hemisphere the situation is slightly better. In fact, at 3° from the south pole is Kappa Velorum, of apparent magnitude +2.5.

Credit: NASA, JPL.

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