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Hi I am running Stellarium 23.2

Meteor showers only appear on the dates they should be visible in the sky

I set the date as -9800 (9800BC) and I see the Taurids appear in Gregorian date May/June.

In -4500 they are in July

Is this due to orbital changes over time, such as orbital precession, or is there an error of some kind?

I have checked the solstice date in 9800BC and that looks OK(ish)

So in -9800 I have the Taurids at the time of the summer solstice

Martin

Think I have my answer - the radiant point does precess enter image description here

This is the source https://arxiv.org/pdf/2207.04506.pdf

MegalthicMartin
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    I'm not sure the Taurids even existed in 9800 BC. The comet causing them is Encke which has an unusually short period of only 3.3 yr. Most comets don't survive more than ~1000 passages. Stellarium probably doesn't consider this though, but it does take Earth's apsidal precession into account. I don't know if this is the explanation though, because it has a period of 112,000 yr, so in 9800 BC our orbit wasn't that different… – pela Sep 04 '23 at 14:04
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    Last I checked, Stellarium used only a Kelperian model for comets. Also a change in the comets orbit would change the radiant point, so they wouldn't still be called the Taurids. You have to be careful about punching in numbers in the distant future/past, as many models that planetarium software uses aren't valid that far out, they cannot be used for anything other than entertainment purposes without research into the specific models used. – Greg Miller Sep 04 '23 at 23:01

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The Gregorian calendar approximates the tropical year (365.2422 days), the mean length of a cycle of seasons. The interval between Earth encounters of a given meteoroid stream is closer to a sidereal year (365.2564 days). The difference between tropical and sidereal years is due to the Earth's axial precession.

Even if the meteoroids' orbit never changes, we can expect the peak date of the shower to shift 0.64 days later per Julian century (36525.0 days) or 1.39 days later per mean Gregorian century (36524.25 days). Try this in Stellarium:

  1. Set keyboard shortcuts to add and subtract 100 sidereal years (Configuration window, Tools tab, wrench button)
  2. Enable Additional information (Configuration window, Information tab)
  3. Select any shower radiant and watch its peak date change over time. There is a discontinuity in 1582 as the calendar switches from Julian to Gregorian.

As @pela and @GregMiller suggest in comments, Stellarium does not account for changes in a meteoroid stream, nor even model it as an orbit. Section 14.6 (pp. 174-177) of the 2023 user guide only lists parameters for an empirical description of the shower.

The Taurid streams are believed to be related to Comet 2P/Encke, whose current orbital period is about 2/7 as long as Jupiter's. Their history is a topic of current research. Egal et al. 2022 Fig. 2 represents a simulated history of the comet's orbital nodes, not to be confused with the trajectory of the comet itself.

Mike G
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