Delta-T

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Delta-T

Victor Engel
Dear Calendar People,

R. H. Gent published a page showing various formulae for approximating delta-T. The last one listed on the page http://www.staff.science.uu.nl/~gent0113/deltat/deltat.htm I suspect has an error, because the values are way off for most years in the 1700s. Given the table, above, it would be more accurate to simply use a constant for those years. Take 1798, for example. Plugging into the formula there, I get about 250 seconds. The table value is 14. The table value from Meeus Astronomical Algorithms for 1798 is 13.

Perhaps it just needs another range from 1700 - 1799 that is a simple curve.

Victor
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Re: Delta-T

Irv Bromberg
From: East Carolina University Calendar discussion List [[hidden email]] on behalf of Victor Engel [[hidden email]]
Sent: Sunday, November 12, 2017 14:34

R. H. Gent published a page showing various formulae for approximating delta-T. The last one listed on the page http://www.staff.science.uu.nl/~gent0113/deltat/deltat.htm I suspect has an error, because the values are way off for most years in the 1700s. Given the table, above, it would be more accurate to simply use a constant for those years. Take 1798, for example. Plugging into the formula there, I get about 250 seconds. The table value is 14. The table value from Meeus Astronomical Algorithms for 1798 is 13.


Is there a reason why you don't use the latest from Stephenson and Morrison et al who have recently published an update of their study of historical eclipses and the Delta T curve. It is freely available from The Royal Society here:


The PDF format is also freely downloadable there.

Supplementary data is available from the URLs given in the manuscript. Supplement S15 contains the cubic splines (3rd degree polynomials) that they have fitted to their data points.

Yours Sincerely, Irv Bromberg, University of Toronto, Canada

http://www.sym454.org/
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Re: Delta-T

Victor Engel
No reason, Irv. Thanks for the link.

Victor

On Sun, Nov 12, 2017 at 6:49 PM, Irv Bromberg <[hidden email]> wrote:
From: East Carolina University Calendar discussion List [[hidden email]] on behalf of Victor Engel [[hidden email]]
Sent: Sunday, November 12, 2017 14:34

R. H. Gent published a page showing various formulae for approximating delta-T. The last one listed on the page http://www.staff.science.uu.nl/~gent0113/deltat/deltat.htm I suspect has an error, because the values are way off for most years in the 1700s. Given the table, above, it would be more accurate to simply use a constant for those years. Take 1798, for example. Plugging into the formula there, I get about 250 seconds. The table value is 14. The table value from Meeus Astronomical Algorithms for 1798 is 13.


Is there a reason why you don't use the latest from Stephenson and Morrison et al who have recently published an update of their study of historical eclipses and the Delta T curve. It is freely available from The Royal Society here:


The PDF format is also freely downloadable there.

Supplementary data is available from the URLs given in the manuscript. Supplement S15 contains the cubic splines (3rd degree polynomials) that they have fitted to their data points.

Yours Sincerely, Irv Bromberg, University of Toronto, Canada

http://www.sym454.org/

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Re: Delta-T

Victor Engel
In reply to this post by Irv Bromberg
Dear Irv,

It took me a while to find this page:

Victor

On Sun, Nov 12, 2017 at 6:49 PM, Irv Bromberg <[hidden email]> wrote:
From: East Carolina University Calendar discussion List [[hidden email]] on behalf of Victor Engel [[hidden email]]
Sent: Sunday, November 12, 2017 14:34

R. H. Gent published a page showing various formulae for approximating delta-T. The last one listed on the page http://www.staff.science.uu.nl/~gent0113/deltat/deltat.htm I suspect has an error, because the values are way off for most years in the 1700s. Given the table, above, it would be more accurate to simply use a constant for those years. Take 1798, for example. Plugging into the formula there, I get about 250 seconds. The table value is 14. The table value from Meeus Astronomical Algorithms for 1798 is 13.


Is there a reason why you don't use the latest from Stephenson and Morrison et al who have recently published an update of their study of historical eclipses and the Delta T curve. It is freely available from The Royal Society here:


The PDF format is also freely downloadable there.

Supplementary data is available from the URLs given in the manuscript. Supplement S15 contains the cubic splines (3rd degree polynomials) that they have fitted to their data points.

Yours Sincerely, Irv Bromberg, University of Toronto, Canada

http://www.sym454.org/