Question

Imagine that the Earth’s rotational axis was tilted 90 degrees rather than 23.5 degrees (so the polar axis would point towards the Sun twice a year). Describe the apparent motion of the Sun and stars over a 24-h period on the winter solstice from (a) the North Pole, (b) the equator, and (c) the South Pole. Note that the Sun’s angular diameter is 0.5 degrees.

Answer 1

On winter solstice the north pole will face to the opposite of the sun's direction and south pole will face towards the sun.

A) At North Pole,

The sky will be completely dark. Directly Above will be Gemini Constellation. Rather than rising and setting all the stars will be circling parallel to horizon over a complete 24h period. The ecliptic will directly go above our heads.

B) At Equator.

Sun will be fixed and rotating at the southern cardinal point at the horizon. It will seem like a forever sunrise. If we include atmospheric scattering no star will be visible. If we can ignore the atmosphere, Gemini will have a fixed rotation at northern cardinal point at the horizon. Rest of the stars and planets will rise at east and set at west. Ecliptic will share the same axis as Earth's rotational axis.

C) At south pole,

Sun will be fixed and rotating directly above (Zenith). If we include atmospheric scattering no star will be visible. If we can ignore the atmosphere, the stars will be circling parallel to horizon over a complete 24h period. The ecliptic will directly go above our heads through sun.