n.dot not changing

[Victor Reijs]

Using 0.15.1.

If I change between VSOP and DE431, and with time 'stopped' the displayed n.dot value is not changed (when hovering over the time).
If I let the time 'run' the n.dot is changed when switching between VSOP and DE431.

All the best,

Victor

[Alexander Wolf (alexwolf)]

Fixed in revision 9025 (trunk)

[Victor Reijs (web-victor-reijs)]

Thanks.
A good 2017!

On 27 December 2016 at 15:10, Alexander Wolf <email address hidden>
wrote:

> Fixed in revision 9025 (trunk)
>
> ** Changed in: stellarium
> Status: Confirmed => Fix Released
>
> ** Changed in: stellarium
> Status: Fix Released => Fix Committed
>
> ** Tags added: archaeoastronomy
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1652762
>
> Title:
> n.dot not changing
>
> Status in Stellarium:
> Fix Committed
>
> Bug description:
> Using 0.15.1.
>
> If I change between VSOP and DE431, and with time 'stopped' the
> displayed n.dot value is not changed (when hovering over the time).
> If I let the time 'run' the n.dot is changed when switching between VSOP
> and DE431.
>
> All the best,
>
>
> Victor
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/stellarium/+bug/1652762/+subscriptions
>

[gzotti (georg-zotti)]

Hmm, I think there is a misunderstanding what should be displayed here:

We have 2 algorithms for the planets, ELP2000 (with nDot=-23.8946) or DE43x (-25.8). If we select some DeltaT algorithm on the Navigation tab of the config panel, then some (usually different) nDot (which belongs to the DeltaT algorithm) is activated. This is the value that should be displayed at this location. I changed this in revision 9031, together with (hopefully) a small optimisation.

It is interesting to observe: Changing to DE431 around -2000 now keeps the moon in (practically) the same position for equal UT, and DeltaT is different by about 40 minutes. This seems to show the positional closeness of DE431 and VSOP/ELP when the nDot compensation is working, right? (I mean, the numerical value of DeltaT is secondary. It is rather LunarPosition(UT) that counts here. Must still compare positions with old eclipse reports...)

[Alexander Wolf (alexwolf)]

Georg, are you understand that nDot was recalculated to the VSOP87/ELP2000 before? And now nDot just always wrong?

[Victor Reijs (web-victor-reijs)]

I think it should display the n.dot of the ephemeris, as that is the only
valid n.dot value (and thus this determine show a DeltaT formula has to be
compensated from the deltaT's formula n.dot).

On 29 December 2016 at 19:27, gzotti <email address hidden> wrote:

> Hmm, I think there is a misunderstanding what should be displayed here:
>
> We have 2 algorithms for the planets, ELP2000 (with nDot=-23.8946) or
> DE43x (-25.8). If we select some DeltaT algorithm on the Navigation tab
> of the config panel, then some (usually different) nDot (which belongs
> to the DeltaT algorithm) is activated. This is the value that should be
> displayed at this location. I changed this in revision 9031, together
> with (hopefully) a small optimisation.
>
> It is interesting to observe: Changing to DE431 around -2000 now keeps
> the moon in (practically) the same position for equal UT, and DeltaT is
> different by about 40 minutes. This seems to show the positional
> closeness of DE431 and VSOP/ELP when the nDot compensation is working,
> right? (I mean, the numerical value of DeltaT is secondary. It is rather
> LunarPosition(UT) that counts here. Must still compare positions with
> old eclipse reports...)
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1652762
>
> Title:
> n.dot not changing
>
> Status in Stellarium:
> Fix Committed
>
> Bug description:
> Using 0.15.1.
>
> If I change between VSOP and DE431, and with time 'stopped' the
> displayed n.dot value is not changed (when hovering over the time).
> If I let the time 'run' the n.dot is changed when switching between VSOP
> and DE431.
>
> All the best,
>
>
> Victor
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/stellarium/+bug/1652762/+subscriptions
>

[Victor Reijs (web-victor-reijs)]

I would display the DeltaT compensated for the n.dot of the ephemeris (and
not the uncompensated DeltaT). Only when compensate it is comparing like
(seconds) with like (seconds).

On 29 December 2016 at 19:27, gzotti <email address hidden> wrote:

> Hmm, I think there is a misunderstanding what should be displayed here:
>
> We have 2 algorithms for the planets, ELP2000 (with nDot=-23.8946) or
> DE43x (-25.8). If we select some DeltaT algorithm on the Navigation tab
> of the config panel, then some (usually different) nDot (which belongs
> to the DeltaT algorithm) is activated. This is the value that should be
> displayed at this location. I changed this in revision 9031, together
> with (hopefully) a small optimisation.
>
> It is interesting to observe: Changing to DE431 around -2000 now keeps
> the moon in (practically) the same position for equal UT, and DeltaT is
> different by about 40 minutes. This seems to show the positional
> closeness of DE431 and VSOP/ELP when the nDot compensation is working,
> right? (I mean, the numerical value of DeltaT is secondary. It is rather
> LunarPosition(UT) that counts here. Must still compare positions with
> old eclipse reports...)
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1652762
>
> Title:
> n.dot not changing
>
> Status in Stellarium:
> Fix Committed
>
> Bug description:
> Using 0.15.1.
>
> If I change between VSOP and DE431, and with time 'stopped' the
> displayed n.dot value is not changed (when hovering over the time).
> If I let the time 'run' the n.dot is changed when switching between VSOP
> and DE431.
>
> All the best,
>
>
> Victor
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/stellarium/+bug/1652762/+subscriptions
>

[gzotti (georg-zotti)]

Alexander, I have seen the previous situation just selected to show either ELP's or DE43x's nDot. Both ephemeris variants should optimally be used with published DeltaT formulae which fit to them directly. If one of the other DeltaT formulae are used, they refer to their own nDots, and their results must be compensated with the correction term. So I find the formulae's nDot values more interesting. The displayed value for DeltaT is independent from this decision, and my changes did not touch numerical/computation results. If you think the ELP or DE43x values should be displayed, we can change it back easily. And we really need a good discussion on this topic in the Guide...

Another observation is the uselessness of some DeltaT formulae which are just approximating polygons through original tables derived from observations (and implemented in other algorithms), they don't bring new information. Some are even problematic, e.g. Schmadel-Zech is a 12th degree polygon which causes absurd faults in antiquity. So there should be also proper handling for dates beyond their range of usability.

[Alexander Wolf (alexwolf)]

Please check this issue on version 0.90.0.9086: https://launchpad.net/stellarium/trunk/0.90.0