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Old 15-05-2019, 06:38 PM
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pfitzgerald (Paul)
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Help Please: Planetarium Software 4 Events BCE

Hi Folks

Which planetarium type software is the most accurate for looking at events during the Iron & Bronze Ages please.

I've looked at the one particular event using SkySafari Pro v5, Stellarium 0.19.0 and the 'old' favourite Voyager 4.5 (All native on the Mac). All three gave different answers.

Has anyone else found this to be a challenge?

Is there another piece of software I should be using instead?

Any help/advice would be much appreciated.

Paul
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Old 15-05-2019, 07:19 PM
gary
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Hi Paul,

What specific event were you looking at?
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Old 15-05-2019, 07:51 PM
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Hi Gary

Halley's comet in 1638 BC as viewed from the Lakes district in England.

Paul
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Old 15-05-2019, 08:14 PM
Wavytone (Nick)
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Can’t be done that far back, due to perturbations in the orbit.

See for example https://en.m.wikipedia.org/wiki/Halley%27s_Comet

“...Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration starting from accurate observations in the seventeenth and eighteenth centuries could not produce accurate results further back than 837 due to a close approach to Earth in that year...” and

“...In 1989, Boris Chirikov and Vitaly Vecheslavov performed an analysis of 46 apparitions of Halley's Comet taken from historical records and computer simulations. These studies showed that its dynamics were chaotic and unpredictable on long timescales...”

I can recall reading both of these analyses. In effect, ultimately the orbit of Halley’s Comet (and most other comets) are perturbed by the masses of the larger planets in ways that make the orbit unstable and unpredictable - in much the same way as the classic mathematics problem of the orbits of 3-bodies are known to be unstable (usually the lightest one ends up being ejected from the system).

Last edited by Wavytone; 15-05-2019 at 08:27 PM.
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Old 15-05-2019, 08:27 PM
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Hi Nick

Thanks for that - I hadn't thought to look for perturbations in its orbit (yet!) - but should have. This probably explains the disparities between the programs.

So although I will not be able tie down a specific date, at least I can surmise that there were times during this period that it would have made an appearance.

Paul
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Old 15-05-2019, 08:46 PM
Wavytone (Nick)
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Paul,

The ephemeris programs all compute comets using a set of orbital elements describing an ellipse which is really only valid for the current orbit. On the longer-lived comets the elements are updated from time to time so people can predict where to find them. At best, only an approximation valid for a short term.

The big problem with a close approach to a planet - as happened in the 9th century - is the orbit would have been totally changed - so much so it’s impossible to make any assumptions about appearances prior to that date. The period, eccentricity and the perihelion position would almost certainly be totally changed so any meaningful prediction is impossible prior to then.

The same effect is exploited by NASA to “slingshot” spacecraft to the outer planets.
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Old 15-05-2019, 08:46 PM
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For anyone else who might be interested in this discussion the following article will be of interest.

http://articles.adsabs.harvard.edu/c...;filetype=.pdf

Paul
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Old 15-05-2019, 09:22 PM
Wavytone (Nick)
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Paul,

In Donald Yeomans 1981 paper the conclusions at the bottom of page 644 contain two interesting points.

Firstly that the positions of comet - earth - sun aren't often favourable for it to be easily seen - ie in dark sky (elongation angle from the sun), and at about 0.25 AU. As he points out, from 1404 bc to 315 bc, there were only two favourable (1266 bc and 1404 bc).

Secondly there is the problem of whether the close approach is before (not so bright) or after perihelion (when its brighter). "... from 240 bc to 1910 there were eight apparitions for which the comet was observable at A < 0.25 au while for the 1404 bc to 315 bc apparitions there were none."

This is interesting because having seen it in 1985-6, there certainly was a huge disparity between its pre and post perihelion appearance. The pre-perihelion appearance was not great and you had to know exactly what you were looking for; many ordinary people simply never noticed it at all. Post perihelion, before dawn it was as plain as your index finger standing above the eastern horizon. But how many would be awake and outside at 3am.... let alone would notice a comet in the sky.

Add to that, two issues regarding the practical aspects of actually seeing something like a comet - from having spent some time there (including the Lake District and in the highlands), and having seen Halley in 1985-6.

Given the high latitude of the UK (and the Lake District) from May - August the nights are very short and twilight lasts for hours. Through summer, the hours of real darkness are extremely limited, so the chances of seeing a less than spectacular comet at low elongations from the sun are quite slim (nil, I suggest) unless it was a really bright "Great Comet" like that of 1910. But... Halley was never a Great Comet, as far as anyone knows. Which suggests an apparition in summer is unlikely to have been seen in the UK, while an apparition from October through winter and spring is more likely to be possible.

And then there's the weather - I can recall some pretty awful winters in the UK where weeks passed between any chance of seeing a clear sky, so its entirely possible that even if it was theoretically visible, it may have been missed entirely. How anyone ever did much astronomy in the UK astounds me.

Last edited by Wavytone; 15-05-2019 at 09:54 PM.
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Old 16-05-2019, 12:26 PM
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Nick

Likewise with the English weather! Having lived in Cambridgeshire for a year I have nothing but admiration for the early astronomers and their perseverance to obtain enough results over time (through generations of observers) to be able to make inferences and predictions.

My interest is looking into some of the stone rings and their astronomical use for setting up a basic calendar as we went from being hunter gatherers to a more sedentary lifestyle with farming.

The Halley's comet aspect was an additional aside for another project. In September 1638 BCE, Voyager 4.5 showed a quite close return for Halley's comet before the autumnal equinox in late October that year. Its altitude was almost at the zenith at midnight on the 22nd.

Thanks once again for your help in pointing out that its orbit would experience perturbations.

Paul
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Old 16-05-2019, 01:13 PM
Wavytone (Nick)
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Paul, the astronomical/calendar interpretation of stone circles and other megaliths has been done to death many times over so no need to go into that here.

There is a paper by Otto Neugebauer concerning the origins of the calendar in antiquity - which, while his focus was the Middle East - contains some ideas equally relevant to the stone circles.
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Old 16-05-2019, 06:14 PM
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Is this the same Neugebauer who looked into Roman catapults as well?

With respect to the astronomical calendar's I've some reading of the articles by Thom etc - but getting a hold of original survey data (for accuracy) is not easy. The main reason I'm going over it now is to see what changes have been made during the past 20+ years and trying to get my own head around it to understand how it was put to use.
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Old 16-05-2019, 07:42 PM
Wavytone (Nick)
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A large problem with most of the megaliths is that most of the stones have been reset by well-meaning types withoit really understanding the consequences - and not just at Stonehenge either. Some of that occurred in the 20th century but some in much earlier times.

Thom realised that, and that it meant interpretation of the surveys could be somewhat doubtful.

http://articles.adsabs.harvard.edu//...00075.000.html

FYI this prolific fellow:

https://en.wikipedia.org/wiki/Otto_E._Neugebauer

I have a copy of his work, reprinted.

Last edited by Wavytone; 16-05-2019 at 08:39 PM.
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Old 17-05-2019, 08:11 AM
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Thanks for sharing these Nick - I'll read Thom's article over the weekend and look at getting a copy of Neugebauer's as well

Paul
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