Tomorrow is the shortest day of the year: 23 hours, 59 minutes, 38.7 secs
en.wikipedia.org
en.wikipedia.org
It's a sine wave with two components. The larger comes from the Earth's elliptical orbit around the Sun. When the Earth is near perihelion in January, it moves faster and farther each day along its orbit, so needs an extra few seconds for more rotation to bring your spot on the surface back under the noon Sun. And the converse in July, where the slower orbital speed at aphelion means each solar noon occurs a few seconds earlier.
The smaller component comes from the axial tilt and runs at twice the frequency (two cycles per year). Near the solstices, the Sun's declination (angle above the horizon at noon) remains nearly constant day to day, so all of its daily motion is in the east-west direction. Near the equinoxes, the Sun's apparent path is more oblique, so some of its apparent velocity occurs in the north-south direction leaving its apparent east-west motion slower. That shortens the solar day since the Earth has to rotate less far to the next solar noon.
The slope of the equation reaches its negative maximum on Sept 16th, so that is the shortest solar day. On this day, the Earth is roughly halfway from aphelion to perihelion, so experiences its greatest orbital acceleration. And it is near the autumnal equinox, where the Sun's apparent east-west motion slows, additively with the same sign as the orbital component, thus creating the global maximum.
It's worth noting all of this refers to "day" as noon to noon or midnight to midnight, affecting daytime and nighttime equally. The phenomenon doesn't affect the daylight/nighttime ratio or insolation or temperatures like the seasonal cycle does.
http://en.wikipedia.org/wiki/Analemma
This is also why the earliest sunset in December 9th (Not the 21st) at 4:12PM
Where? Every location has its own time of sunset...
Leap years and leap seconds are required due to other effects that don't (leap years because of the non-integer ratio between year length and day length and leap seconds because the length of day is increasing slowly)
We disabled leap-seconds at work in our NTP servers, and just use the normal mechanisms to compensate slowly.
How else would you define a day?
Edit: Which 1 minute after posting I realize is the same thing, so forget that half-baked response and instead look at these different ideas of the measure of a day:
Face North (at night) and look right. Everything on that side ascends. In astronomy, East-West distances are measured by how long it takes things to rotate past a fixed observational direction.
Every night, a slightly different chunk of sky will also be directly overhead at midnight, due to the difference observed earlier between solar (sun-relative) day length and sidereal (star-relative) day length.
2.- When we talk about the longest day, we are talking about daylight. That changes according to time of the year because of the inclination of the earth. This is what I originally thought they were talking about.
3.- The usual way to define a day is exactly 24 hours. But this is a little bit different. It is not even exactly a turn of the earth of 360 degrees.
Sidereal day ( https://en.wikipedia.org/wiki/Sidereal_time )
But saying that the longest day happened during the night may be technically true on the South Pole, but still sounds odd.
http://www.timeanddate.com/calendar/june-solstice.html
http://www.govisithawaii.com/2009/08/05/hawaii-fact-34-of-50...
Then there's the fact that the Southern hemisphere experiences "summer" and "winter" at different times of year than the Northern hemisphere.
And for one day my sleep deprivation is also increased by 21.3 seconds.
It's a way to help you prevent yourself from spending too much time on News.YC. If you turn it on you'll only be allowed to visit the site for maxvisit minutes at a time, with gaps of minaway minutes in between. The defaults are 20 and 180, which would let you view the site for 20 minutes at a time, and then not allow you back in for 3 hours. You can override noprocrast if you want, in which case your visit clock starts over at zero.
Noprocrast simply doesn't work for me for that reason.
What's worked best for me is the "Delayed Gratification" extension for Chrome, that delays certain websites for a specific amount of time. I found about 30 seconds is sufficient for me to go be able to convince myself to go back to work most of the time when I find myself just randomly going to a site like Reddit or HN, yet short enough that I can wait out the delay without being too tempted to disable it when I really want to.
Obviously someone got really offended by my amusement.
> These lengths will change slightly in a few years
> and significantly in thousands of years.
That's not what people ordinarily mean by "day" - the boxes on a calendar are all the same size. It's not even what people ordinarily mean by "shortest day" - i.e. the day with the least amount of daylight.
Not only is it a fact of little or no practical utility, it is nearly impossible to verify by reasonable means and therefore for the vast majority of those who assert it to be true it is a revelatory truth accepted on faith. Only those with full notebooks, big telescopes and accurate chronometers have a chance of verifying the hypothesis. Otherwise, it is just part of a canon.
There is no such thing as 'scientism' and science is a method, not a belief system.
There are people who go through life without dogma. Every idea they have can be challenged. Therefore, if you define 'belief' as 'dogmatic belief', as you seem to, they don't have any beliefs at all.