Day length Totally Explained

Everything about Day Length totally explained

Day length, or length of day, or length of daytime, refers to the temporal length of a day, or 24 hours, during which there's daylight.
   Due to the diffusion and refraction of sunlight by the atmosphere, there's actually daylight even when the sun is slightly below the horizon.
   Theoretically, the day length can be computed from the moment the upper limb of the sun's disk appears on the horizon during sunrise to the moment when the upper limb disappears at the horizon during sunset.
   More conveniently, however, the center of the sun is often used in place of the upper limb for computing the day length. When sunrise and sunset do occur, the day length can be computed as 2ω_o/15°, where ω_o is the sunset hour angle in degrees (°) given by the sunset equation. When sunrise and sunset don't occur during the course of a day, the day length is either 0 or 24 hours.
   To considerable accuracy, all the points at the same latitude on the same calendar date can be considered to have the same day length. The contour plot in the figure is computed using the sunset equation.
   Some interesting features that can be easily recognised are as follows:

On the Equator, the length of day isn't exactly 12 hours all the year round, but rather — due to atmospheric refraction and the size of the Sun — exceeds 12 hours by about 7 minutes each day;

Because the sun is north of the equator for almost 4 days more than half the year, the length of the average day at a given latitude in the northern hemisphere exceeds the length of the average day at the same latitude in the southern hemisphere by a few minutes;

At a given latitude, the length of the longest day in the northern hemisphere (on or about June 21) is the same as the length of the longest day in the southern hemisphere (on or about December 21);

Similarly, at a given latitude, the length of the shortest day in the northern hemisphere (on or about December 21) is the same as the length of the shortest day in the southern hemisphere (on or about June 21);

When the northern polar cap of certain range has length of daytime of 24 hours, the southern polar cap of the same range has length of nighttime of 24 hours, and vice versa, except for a few days around the equinoxes. During those periods — about March 19-22 and September 21-24 — both poles experience 24 hours of daytime, due mainly to atmospheric refraction.

In the northern hemisphere, the Arctic Circle is the southernmost latitude where 24-hour daylight can occur at least on one day in a year (northern summer solstice on or about June 21);

In the southern hemisphere, the Antarctic Circle is the northernmost latitude where 24-hour daylight can occur at least on one day in a year (southern summer solstice on or about December 21);

At the poles there's only one sunrise and one sunset in the course of a year. This occurs around the time of the equinoxes.Further Information

Get more info on 'Day Length'.

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://day_length.totallyexplained.com">Day length Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.