Compare Stellarium and SkyMap's lunar eclipse phases

Asked by Victor Reijs

Hello all of you,

I am comparing eclipses with different computer programs. And one of them is Stellarium 0.13.3

So I look at location Babylon: 32.53 Lat,44.42 Long, height 126m
I am using GMT as my home time zone. (Babylon hss 2 hours difference)
DeltaT: Stephenson&Holden 1986
Go to date: -381/6/18
Search Moon and center the view on the Moon so one can observe the earth's shadow when changing time
around 18:09 (GMT) you see the max eclipse.
around 17:02 (GMT) is the start of the umbral phase
around 19:16 (GMT) is the end of the umbral phase

When using SkyMap Pro 11 it reports (also uses Stephenson&Holden 1986):
around 18:09 (GMT) you see the max eclipse.
around 16.47 (GMT) is the start of the umbral phase
around 19:26 (GMT) is the end of the umbral phase

One can see a difference of the start and end of the umbral phase (resp. 15 and 10 minutes).

So I checked some 10 others other lunar eclipses (total or partial, between -720 and -381) and they are ok-ish in Stellarium, when compared to SkyMap Pro 11.
For instance -381/12/12 (total)
Stellarium
around 18:14 (GMT) is the start of the umbral phase
around 21:44 (GMT) is the end of the umbral phase
SkyMap Pro 11
around 18:16 (GMT) is the start of the umbral phase
around 21:42 (GMT) is the end of the umbral phase

So why does the -381/6/18 eclipse have different umbral phases in Stellarium? I can understand a few minutes (as one needs to see the changes in Stellarium with the naked eye, but 15 minutes is considerable [at least for my application]).

Any ideas? Thanks.

All the best,

Victor

P.S. I also checked Swiss Ephemeris and that one has similar results as SkyMap Pro 11

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Revision history for this message
Victor Reijs (web-victor-reijs) said :
#1

I should add that a few lunar eclipses are not really noticeable in Stellarium:
-719/3/8, -620/4/22 and -490/4/25.
All have a small-ish magnitude (smaller than 0.15).
So perhaps the Earth's shadow is too small in diameter? Sorry, I don't yet know why it happens.

Revision history for this message
gzotti (georg-zotti) said :
#2

Hi!

As you certainly know shadow diameter has to be increased somewhat to model effects of earth's atmosphere, and there are differences between (I think) USNO and French traditions. It was also recently mentioned in Sky&Telescope. I don't know (yet) which version Stellarium uses.
I guess details about the Moon will be my next field of investigations&fixes... :-)
BTW for your history work please switch to a current preview build (0.13.65.0 or so) available on this site, it has correct precession, improved application of DeltaT (should not be noticeable in results, but switching algorithm does not cause jumps) and includes nutation (for 1500-2500).

Georg

Revision history for this message
Victor Reijs (web-victor-reijs) said :
#3

I am working on Stephenson's eclipses in his book that determines his
DeltaT formula (I am seeing if we can build a better one, as Stephenson
used some undocumented process;-). I am now with his early eclipses -700
-250 and I am comparing it with three other programs/ephemerii;-).
Normally I use in Stellarium DeltaT=0 (but for debugging I go to a DeltaT
formula that is supported in other programs).
Where can I find these preview builds? Thanks.

On 13 August 2015 at 09:31, gzotti <email address hidden>
wrote:

> Your question #270303 on Stellarium changed:
> https://answers.launchpad.net/stellarium/+question/270303
>
> Status: Open => Answered
>
> gzotti proposed the following answer:
> Hi!
>
> As you certainly know shadow diameter has to be increased somewhat to
> model effects of earth's atmosphere, and there are differences between (I
> think) USNO and French traditions. It was also recently mentioned in
> Sky&Telescope. I don't know (yet) which version Stellarium uses.
> I guess details about the Moon will be my next field of
> investigations&fixes... :-)
> BTW for your history work please switch to a current preview build
> (0.13.65.0 or so) available on this site, it has correct precession,
> improved application of DeltaT (should not be noticeable in results, but
> switching algorithm does not cause jumps) and includes nutation (for
> 1500-2500).
>
> Georg
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/stellarium/+question/270303/+confirm?answer_id=1
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/stellarium/+question/270303
>
> You received this question notification because you asked the question.
>

Revision history for this message
Victor Reijs (web-victor-reijs) said :
#4

Hello George,

Stephenson provides numbers of what the Babylonians 'did' in their
observations regarding the perceiving of the umbral shadow: a diameter of
1.02 +/- 0.03 seems to have been done.
Seventeenth century astronomers were at 1.01 +/- 0.01
(page 83 of his 1997 book).

All the best,

Victor

On 13 August 2015 at 09:31, gzotti <email address hidden>
wrote:

> Your question #270303 on Stellarium changed:
> https://answers.launchpad.net/stellarium/+question/270303
>
> Status: Open => Answered
>
> gzotti proposed the following answer:
> Hi!
>
> As you certainly know shadow diameter has to be increased somewhat to
> model effects of earth's atmosphere, and there are differences between (I
> think) USNO and French traditions. It was also recently mentioned in
> Sky&Telescope. I don't know (yet) which version Stellarium uses.
> I guess details about the Moon will be my next field of
> investigations&fixes... :-)
> BTW for your history work please switch to a current preview build
> (0.13.65.0 or so) available on this site, it has correct precession,
> improved application of DeltaT (should not be noticeable in results, but
> switching algorithm does not cause jumps) and includes nutation (for
> 1500-2500).
>
> Georg
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/stellarium/+question/270303/+confirm?answer_id=1
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/stellarium/+question/270303
>
> You received this question notification because you asked the question.
>

Revision history for this message
gzotti (georg-zotti) said :
#5

> Where can I find these preview builds? Thanks.

On this launchpad page, the big green buttons on the right.

Revision history for this message
Victor Reijs (web-victor-reijs) said :
#6

Sorry, I don't see a big green button on this page (https://answers.launchpad.net/stellarium/+question/270303)

Revision history for this message
Alexander Wolf (alexwolf) said :
#7
Revision history for this message
Victor Reijs (web-victor-reijs) said :
#8

Thanks Alex, I see the most recent is now 0.13.66.0 will download that one

Revision history for this message
Victor Reijs (web-victor-reijs) said :
#9

Hello George,

Just related to this 2% (as used by most people). Danjon sees to have an
improvement (according to Meeus: More mathematical astronomical morsels,
2002, page 143-144):
Danjon, A., "Les éclipses de Lune par la pénombre en 1951," *L'Astronomie*,
65, 51-53 (Feb. 1951).

All the best,

Victor

On 13 August 2015 at 10:50, Victor Reijs <email address hidden> wrote:

> Hello George,
>
> Stephenson provides numbers of what the Babylonians 'did' in their
> observations regarding the perceiving of the umbral shadow: a diameter of
> 1.02 +/- 0.03 seems to have been done.
> Seventeenth century astronomers were at 1.01 +/- 0.01
> (page 83 of his 1997 book).
>
> All the best,
>
>
> Victor
>
> On 13 August 2015 at 09:31, gzotti <email address hidden>
> wrote:
>
>> Your question #270303 on Stellarium changed:
>> https://answers.launchpad.net/stellarium/+question/270303
>>
>> Status: Open => Answered
>>
>> gzotti proposed the following answer:
>> Hi!
>>
>> As you certainly know shadow diameter has to be increased somewhat to
>> model effects of earth's atmosphere, and there are differences between (I
>> think) USNO and French traditions. It was also recently mentioned in
>> Sky&Telescope. I don't know (yet) which version Stellarium uses.
>> I guess details about the Moon will be my next field of
>> investigations&fixes... :-)
>> BTW for your history work please switch to a current preview build
>> (0.13.65.0 or so) available on this site, it has correct precession,
>> improved application of DeltaT (should not be noticeable in results, but
>> switching algorithm does not cause jumps) and includes nutation (for
>> 1500-2500).
>>
>> Georg
>>
>> --
>> If this answers your question, please go to the following page to let us
>> know that it is solved:
>>
>> https://answers.launchpad.net/stellarium/+question/270303/+confirm?answer_id=1
>>
>> If you still need help, you can reply to this email or go to the
>> following page to enter your feedback:
>> https://answers.launchpad.net/stellarium/+question/270303
>>
>> You received this question notification because you asked the question.
>>
>
>

Revision history for this message
Launchpad Janitor (janitor) said :
#10

This question was expired because it remained in the 'Open' state without activity for the last 15 days.