# Perpetual daylight at the South Pole (WWTBAM question) **URL:** \ **Category:** Factual Questions\ **Created:** [September 14, 2004, 5:06pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439 "2004-09-14T17:06:25Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![jsc1953](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@jsc1953](https://boards.straightdope.com/u/jsc1953)\ **Post date:** [September 14, 2004, 5:06pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439/1 "2004-09-14T17:06:25Z")
On yesterday’s “Who Wants to be a Millionaire”, the question was: at the South Pole, for approximately how many months does the sun not set? The choices were: 2, 4, 6, 8. I immediately eliminated 8 – there would have to 8 months of darkness too, and that adds up to more than 12 months a year. My guesses were 2 or 4. So I was quite surprised that the given answer was 6. That would seem to imply that there are 6 months of perpetual daylight, followed immediately by 6 months of perpetual darkness. Doesn’t there need to be some time in between, where the sun rises & sets? And what happens at the poles on the equinoxes? Doesn’t an equinox have 12 hours of daylight, everywhere? ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [September 14, 2004, 5:51pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439/2 "2004-09-14T17:51:50Z")
The Earth’s rotational axis is not perpendicular to the plane of the Earth’s orbit around the Sun. In fact, the rotational axis makes an angle of 23.5 degrees to the orbital plane. This means that in the Northern Hemisphere summer, the North _Pole_ is _always_ facing the sun, and similarly, the South Pole is always facing away from the sun. In the Southern Hemisphere Summer, the South Pole is always facing the sun, and the North Pole is always facing away from the sun. Therefore, each Pole gets approximately 6 months of continuous daylight, followed by 6 months of continuous darkness. Now, within the Arctic (and Antarctic) Circle, you get varying amounts of light, depending on how far north (or south) you are. Anywhere north of 66.5 degrees north, the sun will be below the horizon for 24 continous hours for at least one day of the year (and similarly south of 66.5 degrees south. ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [September 14, 2004, 6:17pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439/3 "2004-09-14T18:17:58Z")
> [@jsc1953](#): > > That would seem to imply that there are 6 months of perpetual daylight, followed immediately by 6 months of perpetual darkness. Bingo. Keep in mind that much of that “darkness” is actually twilight. > [@](#): > > Doesn’t there need to be some time in between, where the sun rises & sets? It takes about 30 hours for the Sun to rise or set at the poles. This interval is considered to be “daylight”. > [@](#): > > And what happens at the poles on the equinoxes? Doesn’t an equinox have 12 hours of daylight, everywhere? With a point Sun and no refraction, every point on Earth would have 12 hours of daylight and 12 of darkness at the equinox. In real life, everywhere on Earth gets a little more than 12 hours, and at the Poles the Sun is on or just above the horizon all day. ---
**Author:** ![jsc1953](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@jsc1953](https://boards.straightdope.com/u/jsc1953)\ **Post date:** [September 14, 2004, 6:24pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439/4 "2004-09-14T18:24:28Z")
Thanks, angua. A related question: on an equinox, when we have 12 hour days in the “northern hemisphere” – how far north is that true? ie, at what latitude are the days longer than 12 hours? (My guess is: the arctic circle). ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [September 14, 2004, 6:36pm UTC](https://boards.straightdope.com/t/perpetual-daylight-at-the-south-pole-wwtbam-question/264439/5 "2004-09-14T18:36:31Z")
At equinox, _all_ points on the Earth have 12 hours of daylight and nighttime. This is because the equinoxes are the only two times that the ecliptic\* and the celestial equator\*\*\* intersect. The ecliptic is not the same as the celestial equator because of the inclination of the Earth’s rotational axis. At the summer (winter) solstice, anywhere north (south) of the Arctic (Antarctic) Circle will have daylight for 24 continuous hours - the “midnight sun”. _Which is the projection of the plane of the Earth’s orbit onto the celestial sphere_\*. \*\*The celestial sphere is is essentially the “night sky” with the North and South Poles of the celestial sphere aligned with Earth’s North and South Poles \*\*\*The equator of the celestial sphere, which divides the night sky into “northern” and “southern” skies