question about relationship between GMST and UT1

Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Thanks!

Michael

On Sep 20, 7:15*pm, wrote:
Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Thanks!

Michael

When you figure out why a leap day or,what amounts to the same thing,
one daylight/darkness cycle is required every 4th year in ending a
1461 day system made up of 365 1/4 rotations of the Earth
corresponding to over 4 complete orbital cycles then maybe you might
discover what you are doing wrong but as you rely on a system which
tries to fit 366 1/4 rotations in an orbital cycle of 365 1/4 days I
would say your problems are far more severe that you can possibly
imagine.

Anyone else think it is pure cruelty in having to explain how a leap
day squares away 4 orbital cycles made up of 365 1/4 rotations per
orbital circuit ?.Maybe if it is phrased this way - what do you expect
from kids when in the care of adults who insist on a nonsensical 366
1/4 rotations for no good reason than it is an outrigger of 'sidereal
time' reasoning ?.

What kind of hatred of astronomy breeds so much hostility to basic
astronomical and planetary facts I cannot say but there must be at
least a few people feeling this and feeling the wrongdoing intensely.

On Sep 20, 1:07*pm, wrote:

rantings of a maniac snipped

Start your own thread, a$$hole...

On Sep 20, 7:15*pm, wrote:
Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Thanks!

Michael

If you invoke 'sidereal time' reasoning ,even as a GMST acronym,you
immediately assume there are 366 1/4 rotations per orbital cycle of
365 1/4 days and that conclusion is about as cruel as it can possibly
get as it means not even arithmetic survives,the normal 365 1/4
rotations make up the calendar convenience of 3 years of 365 days and
1 year of 366 days in dependent only on the ability to count the 1461
daylight/darkness cycles between Mar 1st 2009 and Feb 29th 2012.What
do people think they are playing at ?.There is no way any intelligent
person will go out of their way to ignore the reason for a leap day
and its daylight/darkness cycle which bridges the 6 hour orbital lag
left behind in the previous 3 non-leap years.

What's the big deal with comprehending that the average 24 hour day is
derived from a composite of natural noon cycles spread across the
orbital circuit of 365 1/4 days therefore the 365 1/4 rotations
represent the steady rotation of the Earth coincident with an orbital
period of 365 days 5 hours 49 minutes -

"Here take notice, that the Sun or the Earth passeth the 12. Signes,
or makes an entire revolution in the Ecliptick in 365 days, 5 hours 49
min. or there about, and that those days, reckon'd from noon to noon,
are of different lenghts; as is known to all that are vers'd in
Astronomy. Now between the longest and the shortest of those days, a
day may be taken of such a length, as 365 such days, 5. hours &c. (the
same numbers as before) make up, or are equall to that revolution: And
this is call'd the Equal or Mean day, according to which the Watches
are to be set; and therefore the Hour or Minute shew'd by the Watches,
though they be perfectly Iust and equal, must needs differ almost
continually from those that are shew'd by the Sun, or are reckon'd
according to its Motion." Huygens

http://www.xs4all.nl/~adcs/Huygens/06/kort-E.html

There is no stupid relationship between stellar circumpolar motion and
natural noon,there is just a sampling of the noon average which keeps
the daily cycles fixed to the Sun with the average rotational cycles
never exceeding 365 1/4 rotations for each orbital circuit.The 5 hour
49 minute fraction which makes up the total orbital circumference
beyond 365 rotations is tiny compared 8766 hour total for that circuit
so that the additional 24 hour rotation on Feb 29th is only making up
an orbital distance lost to having the convenience of an orderly
progression of 24 hour days considered as steady rotation at 15
degrees per hour.

Why are people being deliberately obtuse,it is not a matter of being
right or wrong but the quickness to adapt to the technical reasons for
a leap day correction reflected in either the calendar convenience in
itself or the raw planetary cycles which are linked by 365 1/4
rotations per orbital circuit.

wrote:
Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Thanks!

Michael

Sure. At 2000 Jan 01 12:00 UT, the sun was more or less on the meridian
at Greenwich. Remember that the winter solstice was about 9 days
earlier -- at that time the sun was at 18h RA, so add another 9 degrees
so the sun would have been at about 18h36m.

But the equation is for 0h UTC. Midnight at Greenwich, so the local
sidereal time would be 12h opposite to the above -- that is, 6h 36m or
thereabouts.

That 24110 seconds is 6h41m50s. So my BOTE calculation is off by only 5
minutes or so, and that's the equation of time.

-- Bill

On Sep 20, 10:06*pm, oriel36 wrote:
On Sep 20, 7:15*pm, wrote:

[snip]

So what then is the reason for the 7 hour figure in the formula
for converting UT to GMST? I don't get this. I know I'm missing
something simple!

GMST on 1 Jan 2000 at 12.00 UT1 was 18.41. Why? Is this
measured from the previous sunset or??

Michael

On Sep 20, 11:02*pm, Bill Owen wrote:
wrote:

Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Sure. *At 2000 Jan 01 12:00 UT, the sun was more or less on the meridian
at Greenwich. *Remember that the winter solstice was about 9 days
earlier -- at that time the sun was at 18h RA, so add another 9 degrees
so the sun would have been at about 18h36m.

But the equation is for 0h UTC. *Midnight at Greenwich, so the local
sidereal time would be 12h opposite to the above -- that is, 6h 36m or
thereabouts.

That 24110 seconds is 6h41m50s. *So my BOTE calculation is off by only 5
minutes or so, and that's the equation of time.

Hi Bill and thanks very much for this, which I now understand.

What I'm looking for is a formula that gives the UT corresponding to
astronomical midnight at Greenwich each day, which I can then use
to give astronomical midnight for any other longitude.

In my ignorance I thought the standard starting at astro midnight
at Greenwich was the same as GMST (or GAST, which is near
enough to GMST for my purposes). Hence my puzzlement over
the 7h figure.

I need accuracy to within a few seconds.

I originally thought GMST was the way to go, but it seems this
isn't the case?

I'd be very grateful if you could give further advice.

Thanks again!

Michael

On Sep 20, 11:02*pm, Bill Owen wrote:
wrote:
Hi - I'd be grateful for some help with this!

I've found it stated in a few places that

GMST (in seconds at UT1=0) = 24110.54841 + 8640184.812866 * T +
0.093104 * T^2 - 0.0000062 * T^3

where T is in Julian centuries from 2000 Jan. 1 12h UT1

Could someone please explain what that 24110.54841 figure is doing
there. In seconds, this comes to about 7 hours.

When was UT1=0 ? Is GMST about 7 hours in advance of UT1? What am I
getting wrong?

Thanks!

Michael

Sure. *At 2000 Jan 01 12:00 UT, the sun was more or less on the meridian
at Greenwich. *Remember that the winter solstice was about 9 days
earlier -- at that time the sun was at 18h RA, so add another 9 degrees
so the sun would have been at about 18h36m.


Not so fast Bill,you have already locked your observations into the
calendar system by trying to use the convenience of right ascension to
express an orbital characteristic.Right ascension,expressed as
planetary dynamics,works off the idea that the Earth rotates to the
Sun in 24 hours with a .986 degree orbital discrepancy acting as a 3
minute 56 second bridge between the return of a star and the return
to natural noon -

360 degrees = 24 hours
1 degree = 4 minutes
..986 degree = 3 minutes 56 seconds

Hence 24 hours minus 3 minutes 56 seconds = 23 hours 56 minutes 04
seconds.

So what they effectively did in the late 17th century was introduce
366 1/4 rotations to account for an orbital period of 365 1/4 days by
trying to gauge everything off the daily rotation of the Earth.It is
no surprise then that the single orbital daylight/darkness cycle where
the polar coordinates are presently passing through the circle of
illumination as the Earth slowly turns to the Sun is completely
ignored for nothing more than a blizzard of timekeeping average
acronyms.













But the equation is for 0h UTC. *Midnight at Greenwich, so the local
sidereal time would be 12h opposite to the above -- that is, 6h 36m or
thereabouts.

That 24110 seconds is 6h41m50s. *So my BOTE calculation is off by only 5
minutes or so, and that's the equation of time.

-- Bill

On 21 Sep, 05:53, oriel36 wrote:

Always remember Kelleher simulates stupidity to annoy, frustrate and
generally wind-up people.

http://www.martin-nicholson.info/tro...llkelleher.htm

On Sep 21, 7:58*am, Martin Nicholson
wrote:
On 21 Sep, 05:53, oriel36 wrote:

Always remember Kelleher simulates stupidity to annoy, frustrate and
generally wind-up people.

http://www.martin-nicholson.info/tro...llkelleher.htm

It is much easier to explain how the extra rotation of the Earth on
Feb 29th accounts for the fractional 5 hour 49 minutes worth of
orbital motion that is lost each non-leap year so have the orderly
progression of days in a 1461 day system of 3 years of 365 days and 1
year of 366 days.

You have these poor creatures coming here to SAA looking for a formula
that satisfies 'sidereal time' reasoning which assigns 366 1/4
rotations in an orbital circuit off 365 1/4 days but the ins and outs
of it are that a star returns to same observed point in 'sidereal
time' by way of the calendar system of 1461 days.I already explained
in the last response where they attempted to create a 3 minute/.986
degree bridge between the return of a star and the return of the noon
Sun,if people have to fool themselves that it is not based on the
calendar system then so be it but their imaginations are better spent
on the ease of what the leap day and the extra daylight/darkness cycle
accounts for in terms of the 4 orbital circuits of the Earth.

Even allowing for the elaborate schemes which produce 'sidereal time'
reasoning and the nonsensical 366 1/4 rotations in a year,the least I
could expect is that people have some respect for why we have a leap
day daily cycle as it amounts to no more than basic arithmetic.