Do some parts of the world really have 12 hours of daylight each day of the entire year?

Question

I live about 45 degree north latitude. Other then at the Equinox, daylight is seldom 12 hours. Sometimes it is more sometimes less. The summer sun can last 16+ hours.

I understand how and why there is only a single sunrise and sun set at the North and South Poles. But I am trying to get my mind around daylight actually lasting 12 hours every day all year. It seems like the Earth's tilt and our journey around the sun would make it so the amount of daylight is always changing no matter where you are on the Earth.

Answer 1

If you neglect the influence of the terrain/buildings, the atmosphere and the height above sea level, both the time with and without sunlight is very close to 12 hours on the equator (other minor deviations may arise from the non-spheric form of the earth, non-constant rotational speed of the earth and probably some more minor influences). This is due to the equator line always crossing the day-night-border exactly in the middle. This article on latitude has three images (10.-12.) which illustrate this nicely.

These two links also provide explanations for this:

In the Northern Hemisphere, the length of the day is longer during the months when the North Pole is tilted towards the Sun and shorter during the months when it's tilted away from the Sun. The reverse is true for the Southern Hemisphere. The Equator is exactly halfway in between the poles. So it wouldn't make any sense for a day on the equator to be longer when one of the poles is tilted towards the Sun, and shorter when the other one is.

http://curious.astro.cornell.edu/about-us/161-our-solar-system/the-earth/day-night-cycle/195-is-the-sun-always-up-for-exactly-12-hours-at-the-equator-beginner

If you do not consider the atmosphere's influence and calculate sunrise and sunset when the true solar disk is on the horizon, then day and night are equal on the equator.

http://islandnet.com/~see/weather/whys/day_equator.htm

In reality the refraction happening in the atmosphere extends the time in which it is light, depending on models this is estimated at 6-8min.

Answer 2

Imagine for a minute that the Earth is perfectly spherical, that sunlight arrives "from infinity", and that any given spot is either lit or unlit. Then, at any given time, exactly half the surface is in "daytime" and the other half in "night-time". The line separating the two is a Great Circle - a circle with the same centre and radius as the solid sphere.

It should be clear that any other Great Circle on this ideal Earth must intersect this penumbral line and be divided exactly into two equal parts of light and dark.

Now consider the path that any given place on the sphere travels as it rotates. It will move around a line of latitude (i.e. always eastwards). This path forms a circle parallel to the Equator. There is a line of latitude that is a Great Circle, and that is the Equator itself.

So we can deduce that a point on the Equator, in ideal conditions, will spend exactly half the day on the light side and half the day on the dark side of the Earth (except for the case we ruled out where the Sun is exactly over one of the poles).

Answer 3

It is very close to a 12 hour day of light every day in the Southern Philippines. The mountains behind were I live have some effect on shorter afternoon. & the sun rises over the S Pacific. We have about 5 months the sun is in the North side of the house. About 7 months the sun is south side. But on a boat at sea at the equator it could be done. But still on land only 1 day a year were we would have the exact 12 hour day.

Answer 4

At the equator there is about 12 hours year round. This is due to the tilt of the earth. The equator more directly faces the sun than any other part of earth.

http://articles.chicagotribune.com/2011-07-08/news/ct-wea-0708-asktom-20110708_1_equator-length-daylight

Answer 5

Give the check to avanalfen.

Day light is effected by tilt of the earth. The tilt of the earth is what causes seasons.

When the sun is directly overhead absent other factors the split would by 50% 50%.

Only between the tropics is the sun ever directly overhead.

The equator has the least deviation from sun directly over head. At the equator the deviation is about 2 minutes.

But there are other factors. Daylight is extended by the atmosphere refracting the light and gravity bend light (a very small amount). This adds about 7 minutes which is greater than 2 minutes so there is a range around the equator that is more than 12 hours a day year round.