# The Naked Scientists Forum

### Author Topic: What day or time is it?  (Read 1659 times)

#### Joe L. Ogan

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##### What day or time is it?
« on: 22/03/2012 20:50:39 »
Do you know that leap year and 29th of February do not correctly show the proper time (or day)?  I am afraid that we shall never know exactly what time (or day) it really is.  Thanks for comments.  Joe L. Ogan

#### Soul Surfer

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• keep banging the rocks together
##### Re: What day or time is it?
« Reply #1 on: 22/03/2012 21:52:27 »
I am not quite sure what you mean by this question Joe.  Astronomers and others who wish to have a precise time and date reference use Universal time (which is essentially the old Greenwich mean time but more scientific) and the julian date which is the the interval of time in days and fractions of a day since Monday January 1, 4713 BC.

#### Joe L. Ogan

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• Posts: 476
##### Re: What day or time is it?
« Reply #2 on: 22/03/2012 22:18:47 »
I researched this and found that there is no exact way of showing how much time is reflected by the system in use.  It appears that we have either too much time left over after the day increase in February or there is is too little time after applying other systems.  It puzzles me how we can be so exact with missles and other systems that we have.  Maybe there is some way of compensating the inexact time or days reflected.  That is why I asked the question in hopes that someone can explain away the problem

#### David Cooper

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##### Re: What day or time is it?
« Reply #3 on: 22/03/2012 22:39:54 »
The problem is that the Earth doesn't rotate at a speed that points it the same way at the sun at the end of every orbit, and its variable speed of rotation means that even if it did line up perfectly after one orbit it would no longer do so after the next. That's why it doesn't matter how accurately we can measure time, it'll never be possible to get the planet to fit in with it perfectly unless we were to speed up or slow its rotation deliberately to keep it on track (which would obviously be a terrible waste of energy and could never be done properly either). The only solution is the one worked out long ago, and that means adding in extra days here and there so that the official year always ends as close as it can to the same point in the Earth's orbit.

#### CliffordK

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##### Re: What day or time is it?
« Reply #4 on: 23/03/2012 00:10:15 »
Yes,
The problem is that the year and the day are essentially independent measurements.

The day is based on the rotation of the Earth, with noon with the sun at its highest point overhead, and midnight with the sun on the opposite side of the planet (modified with time zones and daylight savings time).

The year is based on the solstices, and equinoxes, based on Earth's orbit around the sun based on the tilt of the planet, and pretty close to 365¼ days.

There are actually several types of "years".

It would be easy enough to make the day longer, equivalent to ¼ day per year....  It would mean adding about 1 minute per day.  The problem is that people would complain that on a 4 year cycle, noon would cycle from the middle of the day to the middle of the night, and back.

#### Joe L. Ogan

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##### Re: What day or time is it?
« Reply #5 on: 23/03/2012 01:03:06 »
I agree with both analysis but that does not answer how we compensate for this variance when we predict when a missle or a space vehicle will arrive.  It looks rather complicated to me.  There must be an answer to this proble,. Thanks for omments.  Joe L. Ogan
« Last Edit: 23/03/2012 02:18:30 by Joe L. Ogan »

#### CliffordK

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##### Re: What day or time is it?
« Reply #6 on: 23/03/2012 07:51:04 »
Either directly, or indirectly, the satellites will be based on either Atomic Clocks, or UT1 based on Earth's rotational period.  The two clocks systems drift apart, but are kept in sync to the nearest second.

Here is a great website for the difference between UT1 and UTC.  I believe the Bull A LOD was used to create this Wikipedia chart comparing UT1 and UTC.

Undoubtedly calculations for interplanetary probe launches are complex, largely based on planetary motion models.  While leap years are easy to deal with, leap seconds could add an element of confusion.

#### simplified

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##### Re: What day or time is it?
« Reply #7 on: 23/03/2012 10:41:36 »
Time is nutrition for energy.

#### The Naked Scientists Forum

##### Re: What day or time is it?
« Reply #7 on: 23/03/2012 10:41:36 »