<p><a href="https://astronomy.stackexchange.com/a/39713/7982">This answer</a> to <em>Any record of the Earth passing through the tail (not trail) of a comet?</em> mentions</p>
<blockquote>
<p>Earth passed through the tail of Halley's Comet in 1910. It caused a bit of a panic due to claims that <a href="https://en.wikipedia.org/wiki/Cyanogen" rel="nofollow noreferrer">cyanogen</a> detected in the tail would cause harm: <a href="https://en.wikipedia.org/wiki/Halley%27s_Comet#1910" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Halley%27s_Comet#1910</a></p>
</blockquote>
<p>and links to the February 8, 1910 New York Times item <a href="https://timesmachine.nytimes.com/timesmachine/1910/02/08/104920328.pdf" rel="nofollow noreferrer">Comet's poisonous tail; Yerkes Observatory Finds Cyanogen in Spectrum of Halley's Comet</a></p>
<p><a href="https://astronomy.stackexchange.com/questions/39712/any-record-of-the-earth-passing-through-the-tail-not-trail-of-a-comet#comment80336_39713">This comment</a> reminds us that its appearance was not unanticipated:</p>
<blockquote>
<p>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 &amp; much of the general public would have also known it was coming.</p>
</blockquote>
<p>And <a href="https://astronomy.stackexchange.com/questions/39712/any-record-of-the-earth-passing-through-the-tail-not-trail-of-a-comet#comment80322_39713">this comment</a> reminds us:</p>
<blockquote>
<p>H G Wells wrote &quot;In the Days of the Comet&quot; 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: <a href="https://en.wikipedia.org/wiki/In_the_Days_of_the_Comet" rel="nofollow noreferrer">In the Days of the Comet</a></p>
</blockquote>
<p><strong>Question:</strong> 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?</p>
<p>Was there any prediction or concern about the Earth passing through the comet's tail?</p>
<hr />
<p><a href="https://i.sstatic.net/uDCzO.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/uDCzOl.png" alt="Comet's poisonous tail https://timesmachine.nytimes.com/timesmachine/1910/02/08/104920328.pdf" /></a> (click for larger)</p>

CC BY-SA 4.0
2020-11-08T04:07:09.350Z
companion question: [What comet's tail did Earth pass through before Halley's?](https://astronomy.stackexchange.com/q/39723/7982)
uhoh
CC BY-SA 4.0
2024-03-23T08:12:39.277Z
Horizons has 30 trajectory files for [1P/Halley](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=NO&COMMAND=1P), going back to 240 BC. [Wikipedia](https://en.wikipedia.org/wiki/Halley%27s_Comet#Computation_of_orbit) says "It was necessary to use ancient Chinese comet observations to constrain their calculations". Here's a [3D plot for 1910](https://gist.github.com/PM2Ring/b1fec75e78cc08f6fc28c6f6c43529c3?permalink_comment_id=4998365#gistcomment-4998365) showing the Sun, Earth and the comet, with a 5 day time step (using Terrestrial Time).
PM 2Ring
CC BY-SA 4.0
2024-03-23T08:18:28.037Z
The Horizons ID for the 1910 file is [90000029](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=NO&COMMAND=90000029). I have some info on the specific angular momentum of Halley's comet [here](https://physics.stackexchange.com/a/765212/123208).
PM 2Ring
CC BY-SA 4.0
2024-03-23T10:11:39.630Z
@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.
uhoh
CC BY-SA 4.0
2024-03-23T11:40:36.007Z
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.
PM 2Ring
<history><comets><halleys-comet>
What were they expecting to see when Halley's comet appeared in 1910?
uhoh
# What were they expecting to see when Halley's comet appeared in 1910?

(Asked by: username_0 on 2020-11-08)

[This answer](https://astronomy.stackexchange.com/a/39713/7982) 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](https://en.wikipedia.org/wiki/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](https://timesmachine.nytimes.com/timesmachine/1910/02/08/104920328.pdf)

[This comment](https://astronomy.stackexchange.com/questions/39712/any-record-of-the-earth-passing-through-the-tail-not-trail-of-a-comet#comment80336_39713) 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](https://astronomy.stackexchange.com/questions/39712/any-record-of-the-earth-passing-through-the-tail-not-trail-of-a-comet#comment80322_39713) 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](https://en.wikipedia.org/wiki/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](https://i.sstatic.net/uDCzOl.png)](https://i.sstatic.net/uDCzO.png) (click for larger)

**Tags:** history, comets, halleys-comet

> **Comments:**
> **username_0**: companion question: [What comet's tail did Earth pass through before Halley's?](https://astronomy.stackexchange.com/q/39723/7982)  
> **username_1**: Horizons has 30 trajectory files for [1P/Halley](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=NO&COMMAND=1P), going back to 240 BC. [Wikipedia](https://en.wikipedia.org/wiki/Halley%27s_Comet#Computation_of_orbit) says "It was necessary to use ancient Chinese comet observations to constrain their calculations". Here's a [3D plot for 1910](https://gist.github.com/username_1/b1fec75e78cc08f6fc28c6f6c43529c3?permalink_comment_id=4998365#gistcomment-4998365) showing the Sun, Earth and the comet, with a 5 day time step (using Terrestrial Time).  
> **username_1**: The Horizons ID for the 1910 file is [90000029](https://ssd.jpl.nasa.gov/api/horizons.api?format=text&MAKE_EPHEM=NO&COMMAND=90000029). I have some info on the specific angular momentum of Halley's comet [here](https://physics.stackexchange.com/a/765212/123208).  
> **username_0**: @username_1 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.  
> **username_1**: 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.  

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## 0 answers

