[NLRS] MORE on gmt question answered (long)

Mon, 5 Apr 2004 09:12:57 -0500

Dave,
a bit more, if you're interested....
UTC isn't completely a "French thing."  There are many time scales, =
depending on what you are doing.  The most common one is "GMT," replaced =
in 1972 with UTC.  The old GMT was based on the rotation of the earth, =
and originated for use in celestial navagation.=20

There are several time scales used in navagation: UT (universal time), =
or UT0, which is based on the rotation of the earth; the number of =
seconds in a day varies from winter to summer because of the position of =
the earth in its orbit about the sun;  UT1, which corrects the yearly =
error of UT0 (and is called GMT - the "mean" part being the mean number =
of second in a day thoughout the year as measured at Greenwich, =
England); UT2, which corrects for the wobble of the earth on its axis; =
and at least one more.  (UT1 is the basis of Civil time in most of the =
world, as well as being used for navagation.)

UTC was adopted in 1972.  Unlike GMT, it is NOT based on the rotation of =
the earth or the earth's orbit; rather it is based on atomic processes, =
specifically an isotope of the Cesium atom.  One second is 9,xxx,xxx.xxx =
transitions of the Cesium 133 (?) atom.  It never varies.  The term =
"UTC" was adopted to keep so it would be similar to the time scales =
already in use.

WWV and WWVH (5, 10, 15, 20 MHz) are the two radio time stations most =
people are familiar with.  CHU, Canada (3.330, 7.335, 14.670 MHz) is =
also available in the US.

WWV broadcasts from Ft. Collins, CO and uses a male voice for =
announcements.  WWVH broadcasts from Hawaii, and uses a female voice.  =
Both provide second "ticks," sometimes encoded with other information.  =
There is no second tick at seconds 29 and 59.  If you listen closely to =
the second ticks at the start of a minute, you may hear "double ticks."  =
These indicate the difference between UTC and UT1 (GMT) in 0.1 seconds.  =
(UT1 is still needed and used for navagation.)  If the double ticks are =
heard in second 1 thru 8, the correction is "plus;" if heard between the =
9th and 16th seconds, the correction is "minus."  Whole "leap seconds =
may be added as often as twice a year to keep UTC and UT1 in step.  If =
they occur, the leap seconds are added at the last second of June 30th =
and December 31st.  All Leap Seconds since 1972 have been "added."  That =
is, the time has gone... 23:59:57... 58... 59... 60... 00:00:00.

England still has not "replaced" the GMT time zone... its still there.  =
They OBSERVE BST, which is offset from the physical time zone they are =
in... there's a difference.  The base time zone is refered to as "Zulu" =
when using UTC.  Most time zones are 1-hour wide: some places though use =
1/2 hour time zones.  Atlantic Standard Time is used in Newfoundland, =
and is -3.5 hours instead of -4 hours.

Time zones originated in the US (Pittsburg, actually) in 1885.  =
Railroads all kept their own time, and it was really confusing when more =
than one RR company served a town.  It could be "noon" several times a =
day !!  Pittsburgh had RR that originated in New Youk and Chicago... two =
hours apart by solar time... so which time should it be in Pittsburg ?

More available if anyone's interested.

73 Donn
WA2VOI/0

-----Original Message-----
From: Dave Aho [mailto:[email protected]]
Sent: Monday, April 05, 2004 1:19 AM
To: NLRS; Steve Bluem; Jay; John McDonald; Charlies Midwest Monsters;
Bill Noble; [email protected]
Subject: [NLRS] gmt question answered

A few replies, and This one sums it up best:

Quote:
Dave,

First, the proper term for the universal time is now
UTC (Coordinated Universal Time) (The French had some
input so the screwy abbreviations). This was put into
place when the official clocks in Greenwich, England
became very inaccurate due to age.

Now there are numerous time standard clocks around the
world. WWV is one of them in the US, the US Navy also
has their own. Canada has CHU.

UTC never changes, ie as in Daylight Saving Time.

However, in England, the time zone GMT is replaced by
BST, British Summer Time, which is +1 hr from UTC.
Likewise we go from CST to CDT, which goes from -6 hrs
UTC to -5 hrs UTC.

Hope this helps.

Bill
AC0W

Unquote.

Thanks Bill.  So in other words, UTC which we use does
not change with the season, but GMT or BST is the UK
local time, and that changes as does our daylight
savings time.  As an aside, apparently at least some
parts of Arizona do not recognize Daylight savings,
and keep one time zone classification throughout the
year....and the same with parts of Australia.

        Dave...N9TTX

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