Can someone explain this?

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Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need to
move the time forward about 10 hours in order to put them together again.
Anyone has an explanation?





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Wasn't it Victor who wrote:
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Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need to
move the time forward about 10 hours in order to put them together again.
Anyone has an explanation?

My guess is that it's caused by the position of your observing point on
the surface of the Earth, and that things would behave as you expect if
the observing point were the centre of the Earth. Or move your observer
to the point on the equator where it's local noon at the instant of
equinox.

--
Mike Williams
Gentleman of Leisure

"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the
vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need to
move the time forward about 10 hours in order to put them together again.
Anyone has an explanation?



I'm not sure, but it may be that the "tropical year" timestep is in current
tropical year lengths, while the Earth's ephemeris calculation is in
terrestrial dynamic time with corrections to UT calculated by extrapolations
of the UT-DT difference formula.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

**** Post for FREE via your newsreader at post.usenet.com ****

Mike,
I have tried setting my position to the center of the earth... same thing.
Thanks anyway

"Mike Williams" escribió en el mensaje
...
Wasn't it Victor who wrote:
**** Post for FREE via your newsreader at post.usenet.com ****

Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the
vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need to
move the time forward about 10 hours in order to put them together again.
Anyone has an explanation?

My guess is that it's caused by the position of your observing point on
the surface of the Earth, and that things would behave as you expect if
the observing point were the centre of the Earth. Or move your observer
to the point on the equator where it's local noon at the instant of
equinox.

--
Mike Williams
Gentleman of Leisure



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Mike,
I have measured how long does Redshift consider a tropical year to be and it
uses 365,242190 days (which is the current ptropical year length) always. So
I went and added up the difference between the current tropical year length
and each year's tropical year length for all years from now to 4004AD. The
total error is only about 3 hours.The displacement I find in the program is
about 10 hours so there are about seven hours which remain unaccounted for.
Another "discovery":
Set the clock to current year's vernal equinox. Set the time step to one
tropical year.Press the step forward button repeatedly. The sun will move
back and forth from the from the vernal equinox apparently randomly with a
tendency to move away from it on the long run. Can you or anyone explain
please it?
Thanks

"Mike Dworetsky" escribió en el mensaje
...


"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the
vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need
to
move the time forward about 10 hours in order to put them together
again.
Anyone has an explanation?



I'm not sure, but it may be that the "tropical year" timestep is in
current
tropical year lengths, while the Earth's ephemeris calculation is in
terrestrial dynamic time with corrections to UT calculated by
extrapolations
of the UT-DT difference formula.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)





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"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Mike,
I have measured how long does Redshift consider a tropical year to be and
it
uses 365,242190 days (which is the current ptropical year length) always.
So
I went and added up the difference between the current tropical year
length
and each year's tropical year length for all years from now to 4004AD. The
total error is only about 3 hours.The displacement I find in the program
is
about 10 hours so there are about seven hours which remain unaccounted
for.
Another "discovery":
Set the clock to current year's vernal equinox. Set the time step to one
tropical year.Press the step forward button repeatedly. The sun will move
back and forth from the from the vernal equinox apparently randomly with a
tendency to move away from it on the long run. Can you or anyone explain
please it?
Thanks

"Mike Dworetsky" escribió en el mensaje
...


"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for the
vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you need
to
move the time forward about 10 hours in order to put them together
again.
Anyone has an explanation?



I'm not sure, but it may be that the "tropical year" timestep is in
current
tropical year lengths, while the Earth's ephemeris calculation is in
terrestrial dynamic time with corrections to UT calculated by
extrapolations
of the UT-DT difference formula.

--
Mike Dworetsky

I would guess that the random shifts come from the actual tropical year
varying slightly due to planetary perturbations from year to year, while the
mean value changes very slowly and smoothly. For example, there are
probably periodic terms with the Venus and Jupiter synodic periods.

As for why the shift is 10 hours rather than 3 hours, I have no idea, but it
possibly has something to do with the way RedShift4 extrapolates the future
rotation of the Earth based on past behaviour. If the formula has quadratic
terms, errors can build up very fast. These would probably be questions
that should be addressed to the company that produced it.

I understand a new version is just out.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

**** Post for FREE via your newsreader at post.usenet.com ****

Thank you Mike, but I just found the answer. It happens that the tropical
year length that I was using is actually the AVERAGE tropical year length.
This number changes depending on where on the Earth's orbit you measure the
tropical year from. So, we have that the vernal Equinox tropical year length
is about 15 seconds longer than the average. These 15 seconds multiplied by
a 2000 year period gives a more than 8 hours error, which is what I get.
Also, the 3 hours gap due to the shortening of the year's length doesn't
apply in this case since the vernal equinox tropical year length has
remained and will remain quite stable for a few millenia due to several
factors like the slowdown of the rotation, the acceleration of the mean
orbital motion, and the effect at the vernal point of shape changes in the
Earth's orbit's that happen to almost cancel out.
If you want more information go to:
http://en.wikipedia.org/wiki/Tropical_year

As I said before, thanks Mike.

"Mike Dworetsky" escribió en el mensaje
...


"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Mike,
I have measured how long does Redshift consider a tropical year to be
and
it
uses 365,242190 days (which is the current ptropical year length)
always.
So
I went and added up the difference between the current tropical year
length
and each year's tropical year length for all years from now to 4004AD.
The
total error is only about 3 hours.The displacement I find in the program
is
about 10 hours so there are about seven hours which remain unaccounted
for.
Another "discovery":
Set the clock to current year's vernal equinox. Set the time step to one
tropical year.Press the step forward button repeatedly. The sun will
move
back and forth from the from the vernal equinox apparently randomly with
a
tendency to move away from it on the long run. Can you or anyone
explain
please it?
Thanks

"Mike Dworetsky" escribió en el
mensaje
...


"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Ok, this is what I do:

I set Redshift's time to 03/20/2004 06h:48m which is the time for
the
vernal
equinox this year
Set the sun's image to "icon". Look at the sun, it is over the
vernal
equinox.
Now enter 2000 and select Tropical years in time step. Press time
step
forward once. The time now is 03/19/4004 15h:55m.
Look at the sun: It has displaced from the vernal equinox and you
need
to
move the time forward about 10 hours in order to put them together
again.
Anyone has an explanation?



I'm not sure, but it may be that the "tropical year" timestep is in
current
tropical year lengths, while the Earth's ephemeris calculation is in
terrestrial dynamic time with corrections to UT calculated by
extrapolations
of the UT-DT difference formula.

--
Mike Dworetsky

I would guess that the random shifts come from the actual tropical year
varying slightly due to planetary perturbations from year to year, while
the
mean value changes very slowly and smoothly. For example, there are
probably periodic terms with the Venus and Jupiter synodic periods.

As for why the shift is 10 hours rather than 3 hours, I have no idea, but
it
possibly has something to do with the way RedShift4 extrapolates the
future
rotation of the Earth based on past behaviour. If the formula has
quadratic
terms, errors can build up very fast. These would probably be questions
that should be addressed to the company that produced it.

I understand a new version is just out.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)







-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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http://www.usenet.com
Unlimited Download - 19 Seperate Servers - 90,000 groups - Uncensored
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

"Victor" no@spam wrote in message ...
**** Post for FREE via your newsreader at post.usenet.com ****

Thank you Mike, but I just found the answer. It happens that the tropical
year length that I was using is actually the AVERAGE tropical year length.
This number changes depending on where on the Earth's orbit you measure
the
tropical year from. So, we have that the vernal Equinox tropical year
length
is about 15 seconds longer than the average. These 15 seconds multiplied
by
a 2000 year period gives a more than 8 hours error, which is what I get.
Also, the 3 hours gap due to the shortening of the year's length doesn't
apply in this case since the vernal equinox tropical year length has
remained and will remain quite stable for a few millenia due to several
factors like the slowdown of the rotation, the acceleration of the mean
orbital motion, and the effect at the vernal point of shape changes in the
Earth's orbit's that happen to almost cancel out.
If you want more information go to:
http://en.wikipedia.org/wiki/Tropical_year

As I said before, thanks Mike.


Now that is both interesting and very subtle. Thanks, I will keep a
bookmark on that page.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)