The Changing Length of Earth’s Day

lod.1973-may2015Preface

Have you ever wondered how long is an Earth day, and is it changing? Well, although the day length is nominally 24 hours, it is not exactly so. It can vary from day to day, as well as from year to year. The amount of change may seem miniscule, and yet it will affect us as early as New Year’s eve, 2016.

A Leap-second will be added on December 31, 2016

http://earthsky.org/human-world/leap-second-june-30-december-31-why-need-controversy

“The U.S. Naval Observatory announced on July 6, 2016 that a leap second will be added to official timekeeping on December 31, 2016. That means your day and year – and everyone’s day and year – will officially be one second longer.”

Earth’s day-length is variable

The U.S. Naval Observatory chart above and article describe the variable length of day, http://tycho.usno.navy.mil/leapsec.html:

“The length of the mean solar day has increased by roughly 2 milliseconds since it was exactly 86,400 seconds of atomic time about 1.88 centuries ago (i.e. the 188 year difference between 2008 and 1820).  That is, the length of the mean solar day is at present about 86,400.002 seconds instead of exactly 86,400 seconds.  Over the course of one year, the difference accumulates to almost one second, which is compensated by the insertion of a leap second into the scale of UTC with a current regularity of a little less than once per year.  Other factors also affect the Earth, some in unpredictable ways, so that it is necessary to monitor the Earth’s rotation continuously.”

Earth’s Day is Getting Longer

http://www.scientificamerican.com/article/earth-rotation-summer-solstice/

Did you know that Earth’s day is getting longer? A tiny bit each year, to be sure, but it’s definitely getting longer and longer for Earth to rotate 360 degrees on its axis.

The Scientific American Magizine has posted an article entitled, “Fact or Fiction: The Days (and Nights) Are Getting Longer” at http://www.scientificamerican.com/article/earth-rotation-summer-solstice/. In this excerpt, NASA explains why.

“ Almost imperceptibly, however, Earth’s day–night cycle—one rotation on its axis—is growing longer year by year, and has been for most of the planet’s history.
“Forces from afar conspire to put the brakes on our spinning world—ocean tides generated by both the moon and sun’s gravity add 1.7 milliseconds to the length of a day each century, although that figure changes on geologic timescales. The moon is slowly spiraling away from Earth as it drives day-stretching tides, a phenomenon recorded in rocks and fossils that provides clues to the satellite’s origin and ultimate fate.”

Although “global warming is expected to shorten the day by 0.12 millisecond over the next two centuries by heating the oceans and changing the distribution of its mass,” clearly the effect of lunar and solar tides is greater by an order of magnitude (at least ten times the effect of global warming).

Today’s daylength

At timeanddate.com, http://www.timeanddate.com/time/earth-rotation.html,

we find that:

“Date: Friday, September 2, 2016
24 hours, 0 minutes, 0.0008836 seconds (0.8836 milliseconds)
This day will be 0.0008836 seconds longer than 24 hours. This is the time it takes Earth to rotate 41.10 cm (16.18 in), as measured at the equator.”

So, on this date the day will be about 0.9 milliseconds longer than 24 hours.

How about calendars?

What about our calendars? The Kanayama Megaliths Solar Calendar will not be affected at all. Why? Because it is an observational calendar. it will always reflect what the sun’s path tells us. Leap years will always be known through the leap-year observations in Iwaya-Iwakage. This is the beauty of the Kanayama Megaliths Solar Calendar. It is and will always be correct.

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