APOD: Comet Tsuchinshan-ATLAS Flys Away (2024 Oct 19)

[APOD Robot]

Comet Tsuchinshan-ATLAS Flys Away

Explanation: These six panels follow daily apparitions of comet C/2023 A3 Tsuchinshan-ATLAS as it moved away from our fair planet during the past week. The images were taken with the same camera and lens at the indicated dates and locations from California, planet Earth. At far right on October 12 the visitor from the distant Oort cloud was near its closest approach, some 70 million kilometers (about 4 light-minutes) away. Its bright coma and long dust tail were close on the sky to the setting Sun but still easy to spot against a bright western horizon. Over the following days, the outbound comet steadily climbs above the ecliptic and north into the darker western evening sky, but begins to fade from view. Crossing the Earth's orbital plane around October 14, Tsuchinshan-ATLAS exhibits a noticeable antitail extended toward the western horizon. Higher in the evening sky at sunset by October 17 (far left) the comet has faded and reached a distance of around 77 million kilometers from planet Earth. Hopefully you enjoyed some of Tsuchinshan-ATLAS's bid to become the best comet of 2024. This comet's initial orbital period estimates were a mere 80,000 years, but in fact it may never return to the inner Solar System.

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[mfavret]

I'm french and I hope you will excuse my poor English.

I think that the fading of this comet during this 6 days (from october 12th to 17th) is not due to the rising distance away from us : going from 70 millions km to 77 millions km just reduce its size of about 10% and brightness about 20% (regarding only the distance from us, but not the configuration Earth/comet/Sun).

My opinion is that the Moon is responsible of this apparent fading : growing from 67% (12) to 100% (17), it lights the sky more and more. Using a shorter exposure to have a correct sky foreground, the photographer produce a relative darker comet, with a lower contrast against the lighter sky.

[johnnydeep]

I'm french and I hope you will excuse my poor English.

I think that the fading of this comet during this 6 days (from october 12th to 17th) is not due to the rising distance away from us : going from 70 millions km to 77 millions km just reduce its size of about 10% and brightness about 20% (regarding only the distance from us, but not the configuration Earth/comet/Sun).

My opinion is that the Moon is responsible of this apparent fading : growing from 67% (12) to 100% (17), it lights the sky more and more. Using a shorter exposure to have a correct sky foreground, the photographer produce a relative darker comet, with a lower contrast against the lighter sky.

Bonjour! Your English is fine. I'd think that the fading is an inherent feature of the comet becoming less active with distance from the Sun combined with it's growing distance from us, rather than just the effect (or mostly so) of a brightening nearby Moon. But I'll leave it to the experts to provide a real answer.

[florid_snow]

There is no certification or evaluation for the title of "expert" astrophotographer, only experience, so I will slightly disagree with Chris here and agree with the commentator who provided order-of-magnitude reasoning. I could claim to be an expert myself, I have decades of experience with astrophotography, but that doesn't matter, there is no real authority from experience that can overturn sound reasoning.

The full moon is bright, and not just a little bit bright, it is incredibly bright, because moon dust is made of tiny glass spheres that reflect sunlight with significant directionality. The brightness of the sky on a full moon night is exponentially brighter than the night before or after, the moon's brightness does not increase linearly with increasing fractional illumination, because of the scattering properties of the little glass spheres of dust.

I will agree with our francophone commentator that the brightness of the comet with respect to the background sky is significantly affected by the brightness of the moon which is also illuminating Earth's atmosphere, increasing the brightness of the sky. The photographer also changed locations from a dark site to a more urban location. All these factors add up to make me think the comet has dimmed in these photographs because of other factors besides distance from the sun.

But that doesn't contradict the message of the image, which is that astrophotography is an ephemeral activity, significantly affected by many other factors, if you want to get a good image, you need 5/5 conditions, not 4 things right and 1 thing wrong, all good conditions are required for a good image. These conditions are: No clouds or moisture in the sky, no urban light pollution, no sky brightness from the moon, no fogging of the lens because of radiative cooling caused by the previous conditions, and finally, no impairment of the photographer, that is to say, caffeine not alcohol.

[Chris Peterson]

I'm french and I hope you will excuse my poor English.

I think that the fading of this comet during this 6 days (from october 12th to 17th) is not due to the rising distance away from us : going from 70 millions km to 77 millions km just reduce its size of about 10% and brightness about 20% (regarding only the distance from us, but not the configuration Earth/comet/Sun).

My opinion is that the Moon is responsible of this apparent fading : growing from 67% (12) to 100% (17), it lights the sky more and more. Using a shorter exposure to have a correct sky foreground, the photographer produce a relative darker comet, with a lower contrast against the lighter sky.

I'm inclined to agree. I haven't seen much change in actual brightness over the last few days (which is something measurable in images), just a loss of contrast caused by increased moonlight (combined with some increased atmospheric moisture in my case).

[Ann]

Am I the only one who takes offense at the spelling, "Comet Tsuchinshan-ATLAS Flys Away"?

Back when I was an English teacher, I would not have let my students get away with that. I would have told them, "You and I fly away, but a comet flies away.

Is the spelling, "it flys", accepted in English these days?

Ann

[johnnydeep]

Am I the only one who takes offense at the spelling, "Comet Tsuchinshan-ATLAS Flys Away"?

Back when I was an English teacher, I would not have let my students get away with that. I would have told them, "You and I fly away, but a comet flies away.

Is the spelling, "it flys", accepted in English these days?

Ann

Well, I consider myself a word nerd, but I didn't catch the misuse myself, and wasn't even sure after you pointed it out. But you are correct.

From https://grammarbrain.com/flys-or-flies/

When to use “flies”
Flies gets used as the plural of the noun fly, which means insect. It is also used as the plural of the verb fly, which means move in the air.

Sentence examples:
I saw a lot of flies sitting on the sweets. I wouldn’t eat it.
The falcon flies in the sky the moment its master gestures.

When to use “flys”
Flys is the proper usage only when “fly” is used as a noun referring to a pant zipper, baseball hits, or other definitions.

Sentence examples:
We all covered the flys on our pants.
There were many flys as the batter went berserk with his hitting.
There were flys lined up in the exhibition.

How to remember which form to use
For all practical purposes, only two meanings of fly get used most often.

One is the insect, and the other moving in the air. For both these words, the rule is very clear.

If you’re flying through the area, the present participle and past participle would be: flies.

For example, “She flies through the air like a bird.”

And finally, usually erroneously attributed to Groucho Marx (and also using the correct usage of "flies"):

"Time flies like an arrow; fruit flies like a banana."

More at https://en.wikipedia.org/wiki/Time_flie ... e_a_banana

[Chris Peterson]

Am I the only one who takes offense at the spelling, "Comet Tsuchinshan-ATLAS Flys Away"?

Back when I was an English teacher, I would not have let my students get away with that. I would have told them, "You and I fly away, but a comet flies away.

Is the spelling, "it flys", accepted in English these days?

Ann

No. What's interesting is that I noticed there was a problem instantly (that jarring feeling that comes from spelling or grammatical errors) but I was distracted by the APOD content and moved on without thinking more about it.

I'm reminded of a semester long class/workshop when I was in college, taught by John Pierce, exploring psychoacoustics and music reproduction (this in the early days of digital music recording). We were evaluating different technologies for accurate musical reproduction (that is, looking at what could produce instrumental sounds from speakers that closely mimicked live performance). We worked with some professional musicians for evaluation, and we quickly learned that they tended to be very bad judges of what instruments and recordings of them actually sound like. Because they couldn't really hear the sound through the music itself. Their brains were focused on bridges and rhythms and key changes, not acoustics. People with poor musical skills did much better in evaluating the actual sound.

This comet has been occupying a lot of my time lately, planning very narrow time slots where it could be imaged, using special equipment, using special processing methods. So when I saw this APOD, that's where my mind instantly went, without paying serious attention to an obvious spelling problem.