I just enrolled in an introductory Astronomy course, and today in lecture the professor asked this question:

Give 4 ways in which the day/night cycle and the seasons would behave on Earth if our rotational axis was in our orbital plane (Uranus is close to this). What about if the rotational axis was perpendicular to the orbital plane (so the ecliptic and Celestial Equator lay on top of each other), but the Earth's orbit was quite eccentric instead of almost circular?

For the first part, it means the Earth is rotating by North/South, right? Would this mean that the day/nights would be "flipped around," i.e. it would be night in a city when it would normally be day. I don't think the seasons would change, since the orbit remains the same.

I don't really know what the 2nd part is saying. Is it simply asking what would change if the orbit was eccentric rather than what it is now?

Any help or clarification on this would be greatly helpful. Thank you!

  • $\begingroup$ Hint: How long would a single day be in the first scenario where the axis was in our orbital plane? Note that a day is the time for the Sun to go from high noon to high noon again. $\endgroup$
    – zephyr
    Commented Feb 9, 2017 at 17:22

1 Answer 1


The Earth's rotational axis is essentially the line connecting the North and South poles. This axis is slightly tilted, making the Earth's equator 23.5 degrees offset from the orbital plane (the ecliptic).

enter image description here From Wikipedia

The first part of the question is asking what would happen if we were to make the rotational axis line up with the orbital plane. That would essentially mean tilting it so that the Earth's equator would be 90 degrees offset from the ecliptic. One way to do this would be to point the North or South pole directly at the sun, or to point it in the same direction as Earth's orbit.

The second part of the question is asking what would happen if the rotation axis was perfectly up and down. This would mean that the equator would not be offset from the ecliptic at all. However, for this part of the question, the Earth's orbit would also be highly eccentric, meaning that our distance to the sun would change a great amount.

I won't post the answer here, since this looks like it is probably a homework question, but to find the answer, first read up about what causes the seasons. To talk about the day/night cycle, think about how the Earth's rotation causes day and night, by moving the sun across the sky. If we changed how the Earth was tilted, how would that affect the seasons? How would that affect where the sun appears in the sky?


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