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When researching for this answer I was looking at Space.com's 2011 article Photos of Halley's Comet Through History

I saw the image below, and read the caption.

Halley's Comet in 1910

enter image description here

NASA/JPL

Halley's Comet as photographed May 13, 1910, by a wide-angle camera at Lowell Observatory, Flagstaff, Ariz., during the comet's last appearance. A streak across the comet near the coma is a meteor trail, and not a scratch on the negative. Streaks at the bottom right are the city lights of Flagstaff Bright spot above the city lights is the planet Venus.

I know that 109 years ago astrophotography wasn't what is is today, but the combination of the overexposed venus, the coincident meteor trails, the non-uniform star trails blending in with the comet's tail breakup along with the unlikely looking "smoke trail" from the upper side of the comet's tail make this photo look quite unusual.

Question: What's going on with that second tail thing above the main tail? The shape looks so unnatural, it seems to have a parallel extent rather than radiate from the coma. What caused this?

between 3:27 and 4:31 a.m. M.S.T. May 13, 1910, Henry L. Giclas, Lowell Observatory

"bonus points" for identifying the photo in some catalog, or in a publication.

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Negatives taken with various intstruments at Lowell Observatory on the morning of 1910-05-13 appear in a 1981 conference paper by Henry L Giclas. The wide-angle images were taken with cameras piggyback on a telescope tracking the comet nucleus. These exposures are naturally deeper in the center than at the edges; modern astrophotographers take flat fields to correct for this. The stars in the upper right of the image in question were low enough to the horizon to be obscured for part of the exposure, making their trails shorter. To make this more intuitive, rotate the image so that the tail points to the right and upward.

Comet tails generally have two parts: a smooth, curved dust tail driven by steady radiation pressure; and a straight, blotchy plasma tail (also called an ion tail or gas tail) driven by the fluctuating solar wind. A coronal mass ejection can severely disrupt the latter, as the STEREO spacecraft observed with Comet Encke in 2007.

The 1910 image in question may show a tail disconnection event in progress. If so, the highlighted feature is the old plasma tail drifting away from the nucleus, and the new plasma tail is not yet large enough to be distinct. Barnard 1914 includes three photos of such an event on June 6-7, 1910.

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  • $\begingroup$ Thank you for digging up this reference so quickly! $\endgroup$ – uhoh Feb 20 '19 at 15:41
  • $\begingroup$ I've added a 2nd image with an arrow, I don't think this is a typical dust tail nor a gas/plasma tail either. It abruptly jumps out from the side. $\endgroup$ – uhoh Feb 27 '19 at 6:32
  • $\begingroup$ Added a paragraph to answer @uhoh's comment. $\endgroup$ – Mike G Feb 27 '19 at 16:41
  • $\begingroup$ excellent, I'd never heard of such a thing but it makes sense, thanks! :-) $\endgroup$ – uhoh Feb 27 '19 at 23:28

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