Hello, I am using Starry Night Pro for archeoastronomy. Can you tell me the actual calculation used for the (very ancient) Earth pole location (circa 12,000 BC)? Comparing Starry Night to my own calculation, using a longterm earth pole motion model from the astrophysical literature, I get about 0.3 degrees difference, over that timeframe (14,000 years). Thank you.
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Thomas Brophy Hi, A clarification... Starry Night re-posted my question to their support here, with this message, "Thank you for contacting Starry Night Support. This is the kind of advanced question that is perfect to ask in the Community Help forum for general astronomy"
--I think maybe they did not understand my question. This is not a general astronomy question. I need a reference to the (presumably published) calculation method they use to calculate the very ancient pole of earth. But, maybe someone here can answer that?
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Thomas Brophy Hi All, Here is a further clarification of my question:
My version of Starry Night Pro (6.4.3) shows Vega culminating North at a declination of 86.2407 degrees, 12008 BC. The discrepancy is that I calculate Vega culminating North at declination 86.54 degrees, 12070 BC. I use the obliquity and precession model published by A.L. Berger (1976. Obliquity and Precession for the last 5,000,000 years. Astron. & Astrophys. 51, 127-135). I think that has become a standard calculation method used, for example, by climate change modelers, and considered relatively accurate especially for the recent past (last precession cycle or so). The difference between my value and Starry Night's value (for the declination) is not due to our very slightly different proper motions. Starry Night quotes a proper motion for Vega (0.2008, 0.2872) (RA,Dec) arcsec/year. The current SIMBAD website quoted values are (0.20094, 0.28623) [same units]. I used (0.20103, 0.28747) which was at the time the SIMBAD quoted value. That is clearly not the issue because those differences in proper motion yield less than 0.002 degrees differences over 14,000 years. (Compared to the 1.36 degrees movement of the whole proper motion itself.) The ΔT calculation can not be the source of the different culmination declinations (about 0.3 degrees difference). That difference is due to the calculated orientation of Earth’s pole. My question is how does Starry Night Pro calculate Earth’s pole during that epoch (circa 12,000 BC)?
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Thomas Brophy One more clarification: the title of this question should actually be something like "How does STARRY NIGHT PRO calculate the ancient pole of Earth?" Please reference or publish this calculation, similarly as you referenced the NASA site as your source for Delta T calculation (which is the ancient spin rate of Earth). ...OK, Happy Easter:-)
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Marko Kudjerski Hello Thomas, we apologize for the confusion.
The community help forum for General Astronomy should really have a full name of "General Astronomy as it relates to Starry Night". As the forum is often visited by our staff and as the topic is of interest to other users of Starry Night I have reposted the question here.
In terms of the answer to your question, in the version that you have (6.4.3) Starry Night is using the paper by Williams ( James G. Williams, "Contributions to the Earth's obliquity rate, precession, and nutation," Astron. J. 108, 711-724 (1994)). However, recently it has come to our attention that some of the coefficients we've been using in the calculations for version 6.4.3 are off (and the coefficients have been updated in our original source). Our calculations are coming from Astronomical Almanac and are based on the following: http://astronomical-almanac.sourcearchive.com/documentation/5.6-3/precess_8c-source.html .
The updated version of the algorithm is already in our codebase and is awaiting the the next Starry Night update (your software will inform you once the update is available).
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Thomas Brophy Thanks to Marko et al. for addressing this. I look forward to the fix. Generally, by the way, I think Starry Night is an excellent program.
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Hendrik Dirker ALL astronomy software is fatally flawed in simulating precession, due to grossly misconstrued Earth orbital mechanics. The ACTUAL gyration cycle is substantiated in this article:
http://sites.google.com/site/earthgyration/
and subpage:
http://sites.google.com/site/earthgyration/Home/climate-change -
Hendrik Dirker On the topic of ancient pole stars - as stated, precession simulating software is fed with 'classical' data to reproduce 'classical precession'.
Following the path of true polar wander...
Expounded upon from an astro-archaeological and historical perspective, the celestial pole as determined by the orientation of Earth's axis into space, in words not algorithms - see my post over at GHMB:
http://grahamhancock.com/phorum/read.php?1,1044643
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