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Wednesday, October 16, 2024

Comet C/2023 A3 (Tsuchinshan-ATLAS) over the Gateway Arch in St. Louis - October 16, 2024

By DAN ROBINSON

Editor/Photographer

I went into downtown St. Louis five nights in a row for Comet C/2023 A3 (Tsuchinshan-ATLAS) from October 13-17, then a sixth time in rural Clinton County, Illinois on the 18th. The best results came from the 4th try on Wednesday night (the 16th) when we finally had crystal-clear skies free of clouds and smoke:

Comet Tsuchinshan-ATLAS over the Gateway Arch in St. Louis

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The following night (Thursday the 17th) skies were clear again, allowing a fifth trip fo capture some additional angles:

Comet Tsuchinshan-ATLAS over the St. Louis skyline

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The Arch's bright LED floodlight illumination and the relatively dim comet required these to be two-frame blends of back-to-back exposures of 0.4 seconds and 6 seconds.

Capturing this comet over downtown was quite the saga, requiring 5 attempts between Sunday the 13th and Thursday the 17th. On Sunday night the 13th, I saw a large object resembling an aurora pillar in the western sky in the general location and orientation as the comet was advertised to be. I made a run into downtown to capture it, but lost the feature in the city lights. Monday night the 14th, I made another attempt, doing several exposures looking for the feature I'd seen the previous night. Instead, I finally got a visual on the comet, and it was much smaller and dimmer than what I saw Sunday night. I'm not sure what I was seeing Sunday. On Monday night, the comet was only faintly visible in the city lights as thick cirrus clouds contributed to muting its brightness.

On Tuesday evening the 15th, I went back into the city as skies looked better. There were some midlevel stratocumulus intermittently blocking the comet, but skies were otherwise clear beyond those. But there was a new problem: a large warehouse fire, buring for days, north of downtown was riding the northerly winds right over the city, again blocking the full brightness of the comet. Despite this, I got a better series of exposures, but again it was muted by the smoke which also was catching the light from the Arch's floodlights and further reducing the contrast. This is a 50mm 2-frame blend of exposures set for the Arch and for the comet:

Wednesday and Thursday nights finally featured a crystal-clear sky, and produced the best results. Those two images are at the top of this post. The first image was the best of the week, with the longest tail visible out of all of the previous attempts. Again, these exposures are two-frame blend of back-to-back 6-second and 0.4-second exposures - the only way to have proper exposures of the very dim comet and the Arch's new overpowering-for-astrophotography LED floodlights.

With the St. Louis city compositions captured to my satisfaction and another clear night available, I turned to getting a few low-light rural shots on Friday the 18th. I went out to my go-to astrophotography foreground: the railroad crossing east of New Baden that has minimal nearby artificial light sources in all directions. I wanted to get at least one good comet-only shot on the 50mm lens. This at 50mm, 6 seconds at 800ISO and F1.8: