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***Mid-Season Posters Poll***

Re: ***Mid-Season Posters Poll***

norm1909 said:
Actually, not to be mean, but it is Greenwich Mean Time, though admittedly, the average Joe sometimes calls it Greenwich Meridian Time because it is measured from the Greenwich Meridian Line at the Royal Observatory in Greenwich.;)

Seriously, it is of a math origin - GMT is Greenwich Mean Time is the mean (average) time that the earth takes to rotate from noon-to-noon.
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I knew I could count on you to chime in on this, but the use of "mean" there is a little strange. The mean that you refer to is actually the old definition (before UMT) definition of 24 hours - the time required for a noon to noon rotation of the earth. Divide that by 24 and you have the length of an hour. Divide that by 60 and you have a minute, divide that by 60 and you have a second. Now we define a second in terms of the number of cycles in the natural vibration of some crystal (which I don't know, and I'm too lazy to look up).

Statistically speaking that is where the use of the Mean comes in. I presume that when we say that it is 1300 GMT that on an average day, that the Royal Naval Observatory would have completed 1/24 of its daily noon to noon rotation.

You should admit, however that even your site says that it can be (correctly) referenced as Greenwich Meridian Time.
 
Re: ***Mid-Season Posters Poll***

NUProf said:
I knew I could count on you to chime in on this, but the use of "mean" there is a little strange. The mean that you refer to is actually the old definition (before UMT) definition of 24 hours - the time required for a noon to noon rotation of the earth. Divide that by 24 and you have the length of an hour. Divide that by 60 and you have a minute, divide that by 60 and you have a second. Now we define a second in terms of the number of cycles in the natural vibration of some crystal (which I don't know, and I'm too lazy to look up).

Statistically speaking that is where the use of the Mean comes in. I presume that when we say that it is 1300 GMT that on an average day, that the Royal Naval Observatory would have completed 1/24 of its daily noon to noon rotation.

You should admit, however that even your site says that it can be (correctly) referenced as Greenwich Meridian Time.
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LOL, the Mid-Season blues.

Additionally, if one knows the circumference of the earth at the point at which they are standing (X), they can compute the speed at which that point is rotating - X/24 MPH.

Also, I did choose that site, as it mentions both names, this site, makes no mention of Meridian.

The Leap Second :eek:

INTERNATIONAL EARTH ROTATION & REFERENCE SYSTEMS SERVICE complete with atmospheric excitation now were talking:p :p
 
Re: ***Mid-Season Posters Poll***

Yes, but the first site you mentioned appears to be more official :D

There is a nice history of the GMT/UTC system here.
 
Re: ***Mid-Season Posters Poll***

NUProf said:
Now we define a second in terms of the number of cycles in the natural vibration of some crystal (which I don't know, and I'm too lazy to look up).
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9,192,631,770 vibrations of the Cesium-133 atom

norm1909 said:
The Leap Second :eek:
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And this definition of a second is where the leap second comes into play...
The first leap second was added on June 30, 1972. Since then, they have occurred at an average rate of less than one per year. Although it is possible to have a negative leap second (a second removed from UTC), so far, all leap seconds have been positive (an extra second has been added to UTC). Based on what we know about the earth's rotation, it seems unlikely that we will ever have a negative leap second.

Leap seconds are needed so that users of the astronomical time scale (UT1) can use UTC and know that the difference between the two time scales is never greater than 0.9 seconds. Currently the difference between UT1 and UTC is changing at a rate that requires the addition of less than one leap second per year. When a leap second is necessary, an announcement is made at least several months in advance, and all leap seconds so far have been implemented on either June 30th or December 31st.
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Thus, the length of a second is constant, the number of seconds in a minute is usually 60, but may be 61 on occasion or, should the Earth's rotation speed up slightly, 59. The number of seconds in an hour or a day varies with the number of seconds in the minutes making them up. Thus, while 1 day is usually 86,400 seconds, it can also be 86,401 or 86,399 seconds. The length of the second is the only constant.
 
Re: ***Mid-Season Posters Poll***

Can you think of any other hockey forum where discussion of creating a poll could possibly morph into a discussion of the definition of the second?
 
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Re: ***Mid-Season Posters Poll***

http://www.infoplease.com/ipa/A0002063.html

Sidereal time. A sidereal day is the time that it takes the Earth to complete one rotation on its axis so that a particular star can be observed twice at the meridian that runs directly overhead. Because the Earth is moving around the Sun as it rotates on its axis, the sidereal day is about 4 minutes shorter than the solar day, being equivalent to 23 hours, 56 minutes, and 4 seconds in mean solar time. As a result, a star will appear to rise about 4 minutes earlier every night, and different stars will be visible at different times of the year. Astronomers use a point that they call the “vernal equinox” to determine local sidereal time
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So a day really isn't 24 hours now is it?
 
Re: ***Mid-Season Posters Poll***

11 polls in....

....and I'm fine with my thread being hijacked and spinning into a discussion on time.

In fact, if you have the time(no pun intended), and want a philosophical view of time, St. Augustine has a whole chapter on it(Book XI) in his Confessions, I think it's titled 'Time and Eternity' or it may not be titled at all, just Book XI. It may make your head spin though, its conceptual.
 
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