This answer to Any record of the Earth passing through the tail (not trail) of a comet? mentions

Earth passed through the tail of Halley's Comet in 1910. It caused a bit of a panic due to claims that cyanogen detected in the tail would cause harm: https://en.wikipedia.org/wiki/Halley%27s_Comet#1910

and links to the February 8, 1910 New York Times item Comet's poisonous tail; Yerkes Observatory Finds Cyanogen in Spectrum of Halley's Comet

This comment reminds us that its appearance was not unanticipated:

Astronomers of that time certainly knew when to expect Halley's Comet. After all, this was its third appearance after Edmond Halley's famous prediction. It seems reasonable to think that Wells & much of the general public would have also known it was coming.

And this comment reminds us:

H G Wells wrote "In the Days of the Comet" in 1906, in which the earth passes through the tail of a comet. I don't know if astronomers of the time had predicted the Halley event 4 years early: In the Days of the Comet

Question: What exactly were astronomers expecting prior to the comet's arrival? Did they have a predicted orbit, time of appearance and closest distance to Earth and estimated brightness prepared? If so, how close did the predicted behavior match the actual?

Was there any prediction or concern about the Earth passing through the comet's tail?

Comet's poisonous tail https://timesmachine.nytimes.com/timesmachine/1910/02/08/104920328.pdf (click for larger)

  • $\begingroup$ companion question: What comet's tail did Earth pass through before Halley's? $\endgroup$
    – uhoh
    Commented Nov 8, 2020 at 4:07
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    $\begingroup$ Horizons has 30 trajectory files for 1P/Halley, going back to 240 BC. Wikipedia says "It was necessary to use ancient Chinese comet observations to constrain their calculations". Here's a 3D plot for 1910 showing the Sun, Earth and the comet, with a 5 day time step (using Terrestrial Time). $\endgroup$
    – PM 2Ring
    Commented Mar 23 at 8:12
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    $\begingroup$ The Horizons ID for the 1910 file is 90000029. I have some info on the specific angular momentum of Halley's comet here. $\endgroup$
    – PM 2Ring
    Commented Mar 23 at 8:18
  • $\begingroup$ @PM2Ring Excellent! I did ask What? rather than when or where (i.e. did they expect something small, or fearful in size?) but these will likely be a perfect answer to a "when and where" follow-up question. $\endgroup$
    – uhoh
    Commented Mar 23 at 10:11
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    $\begingroup$ Right. I can't answer the "what exactly" questions. ;) The current solar system theory was Newcomb's, which was still the basis of ephemerides into the 1980s, when it was superseded by the JPL DE. They knew from perturbation calculations that there was a 43 arcsec/century anomaly in the precession of Mercury. OTOH, calculating perturbations on an inclined retrograde eccentric orbit requires much more number crunching, and the random-ish mass loss near perihelion doesn't help. $\endgroup$
    – PM 2Ring
    Commented Mar 23 at 11:40


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