# Polar Day/Night

This is my first question so any feedback is appreciated! I basically have an Earth analog that has an axial tilt of approximately 12 degrees instead of Earth's 23, and I wanted to find out how I could approximate the length of the longer polar nights the flora and fauna would be subjected too. Thanks!

Edit: I would also like to know how I could approximate how much of the planet would be affected by this polar night, as in what latitude to the pole would the polar night cover.

• Axial tilt doesn't matter. The longest polar night will still be half a year, as will the longest polar day. Those happen only exactly at the poles, though. The length of the longest polar day or night decreases from the pole to the polar circle (at 78 degrees latitude in your story), where there is exactly one day (at the summer solstice) and, half a year later, one night (at the winter solstice) longer than a full solar day. – AlexP Jun 28 '18 at 3:42
• @AlexP you could elaborate that into an answer. – The Square-Cube Law Jun 28 '18 at 3:56
• @Renan: OK done. – AlexP Jun 28 '18 at 4:40

## 1 Answer

Axial tilt doesn't matter. The longest polar night will still be half a year, as will the longest polar day. Those happen only exactly at the poles, though. The length of the longest polar day or night decreases from the pole to the polar circle (at 78 degrees latitude in your story), where there is exactly one day (at the summer solstice) and, half a year later, one night (at the winter solstice) longer than a full solar day.

The relationship between the axial tilt angle $\theta$ and the latitude of the polar circle, $90^{\circ} - \theta$. The planet is shown at the summer solstice. Own work, available on Flickr under the CC BY-2.0 license.

As shown in the picture, the pole stays in the light for one half the year, and then will go into the shadow for the next half. A point exactly on the polar circle, at a latitude equal to 90° minus the angle of axial tilt, on the day of the summer solstice will remain in the light for one full rotation; the daytime will be almost three full solar days. Any point between the northern and the southern polar circles will never experience a day or a night longer than one full solar day; but, of course, near the polar circle the night time (or the day time) can be very brief. For example, on our Earth, Leningrad is famous for its white nights.