Comet Tsuchinshan-ATLAS C/2023 A3, again

Here is what will probably be my best picture of the comet, as it is now receding from the sun and getting dimmer. From a reasonably dark site outside of Athens, Georgia, I could see it faintly with the unaided eye, and clearly with binoculars.

Comet FAQ (C/2023 A3 Tsuchinshan-ATLAS)

Q. Is this something that only happens every 50,000 years?

A. We get a bright comet every few years, just not the same comet. Many comets have very long orbits (estimated at 10,000 years or more) although quite a few are shorter (down to just 3 years or so). So... Seeing THIS comet is rare; seeing SOME comet is not. We had a bright one in 2020, if you remember.

Q. Will it "streak across the sky"?

A. Not like a shooting star. It will take weeks to move gradually across the night sky. See the map below.

Q. How bright is it?

A. [Updated.] Probably bright enough to see without binoculars, at least for the first few days; definitely visible in binoculars. The brightness of comets is hard to predict. This one will get farther away from the sun, higher up in the evening sky, but dimmer, as time goes on.

Q. How did it get its name?

A. Comets are named after their discoverers. This comet was jointly discovered by professional teams at the Purple Mountain Observatory (Zijinshan, sometimes spelled Tsuchinshan) in China and the Asteroid Terrestrial-impact Last Alert System (ATLAS) in South Africa; the latter is an observing program that normally looks for asteroids that might hit the earth, but also picks up other fast-moving objects in the Solar System.

This map is for observers in the contiguous 48 states. My understanding is that Sky and Telescope allows it to be shared freely.

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How to communicate quickly

Look at the style of the "Comet FAQ" above. I offer it as an example of how to write things that can be read quickly and will communicate effectively.

It is organized around questions the reader already has in mind. I don't define any terms or frame any questions before starting.

Each question is short, and the answer is in the very first sentence of the reply. The rest of the reply then adds information.

I recommend this as a style of writing. The FAQ file may be the most important literary genre invented in my lifetime.

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Christianity and the history of science, continued

I'm continuing my course on Christianity and the history of science at Alps Road Presbyterian Church. It has been very well received. I think it's important that Christians must not be afraid of science or feel that they are somehow forbidden to know about it.

Here are links to three more talks that are now on YouTube. The entire set is on the church's YouTube channel. There will be 10 in all.

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Comet Tsuchinshan-ATLAS C/2023 A3

This evening (October 11) I managed to see and photograph the highly publicized comet that has just entered the evening sky, after giving a good show (which I did not witness), mainly in the Southern Hemisphere, while it was on the sunrise side of the sun.

The circumstances were a comedy of errors. The Athens Astronomy Club gathered at Sandy Creek Park, but we had all almost completely concluded that the comet was still too close to the sun and too low in the sky after sunset. Adding to the fiasco, I had gotten there with no memory card in my camera.

But I decided to take one last, long look with binoculars — and found the comet, very low down in the last glow of sunset. Soon everybody was looking at it. And someone lent me an SD card for my camera.

So, under very adverse conditions, I used my Nikon D5300 to take a single 1/30-second exposure with a 105-mm lens at f/2.8, at ISO 1600, on a fixed tripod. (Memo: Next time, use ISO 400 or 200. This is only a really low-noise camera at low speeds.) After some cropping and processing, this yielded the blurry, grainy picture you see here. But I did photograph the comet, at 7:48 p.m. EDT on October 11, when it was still too close to the sun for most observers.

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Aurora borealis in Georgia — again

The earth had another auroral storm last night, predicted a day or so in advance, and I've been seeing pictures of the aurora from such unlikely places as Valdosta, Georgia; Cambridge, England; and Sydney, Australia.

I wasn't able to get out into the country for this one, but I was able to photograph it, and barely see it, from my own driveway in Athens, Georgia.

I took a camera outside to check for it, since it shows up much better on even the simplest photographs than to the unaided eye. For the most part, what we saw in Georgia was a SAR arc (stable auroral red arc), which, I'm told, is due to electric currents induced in the ionosphere, rather than the direct impact of particles from the sun onto the north and south magnetic polar regions (those produce green curtains and streamers).

As you can see above, the main display was a red stain on the sky — simply a large reddish patch fairly high up in the northeast. Later it moved toward Cygnus in the northwest, and the camera picked up a red background very high up, but almost featureless. With my eyes I could see that the sky was slightly lighter than it ought to be, particularly to the left of Cassiopeia — something that a person not familiar with the appearance of the sky from here would not have noticed. I don't think I would have detected the aurora without a camera.

For a brief period, there were streamers in the north, which confirmed that this was really an aurora and not some kind of reddish city lights. I was able to see the main streamer very faintly with my eye — the eye of an experienced galaxy observer, sensitive to slight variations in the dark gray background. Out in the country, people could probably have seen it fairly easily.

That was the second auroral storm of 2024. I've slightly updated my entry about how to know whether there's about to be an aurora. Thanks to NOAA, we get predictions and information that we never could have gotten in the past. When I was starting out, in the 1970s, an auroral storm like this was something we would read about two months later in magazines; there was no easy way to be alerted to it as it was happening, although I think there was a ham radio net for aurora alerts, which I ignored because aurorae are so rare in the South.

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A feast of astrophotography
M33 partly resolved into stars

On the evening of October 2, we had reasonably clear weather, and I had a good, long astrophoto session with my 8-inch telescope in my driveway. Let's start with perhaps my best astronomical photograph ever, the galaxy M33 partly resolved into stars. Yes, as you can confirm by comparing to the maps in the November Sky and Telescope, some individual stars in the galaxy are plainly visible (as well as unresolved star clouds, and stars in our galaxy in front of it).