<p>Space.com's <a href="https://www.space.com/comet-leonard-fading-maybe-splitting" rel="nofollow noreferrer">Comet Leonard, the brightest of the year, is fading and acting strange</a> seems to be full of inexact language, like &quot;something's wrong&quot; and &quot;unhealthy&quot; and &quot;goner&quot; and &quot;the comet's heart could also implode&quot;:</p>
<blockquote>
<p>&quot;It's not great news. The comet should be brighter and brighter,&quot; Quanzhi Ye, an astronomer at the University of Maryland who specializes in comets, told Space.com. &quot;If it's not getting brighter then <strong>something's wrong</strong>, but we don't know exactly what at this stage.&quot;</p>
</blockquote>
<blockquote>
<p>&quot;Why it's fading, there are all kinds of hypotheses,&quot; Ye said. &quot;The simplest and the most obvious one is <strong>something unhealthy is happening</strong> to the comet.&quot;</p>
</blockquote>
<blockquote>
<p>There are several factors that could break apart a comet, Ye noted. The gravitational tug of the sun or a large planet could pull it apart, sure, <strong>but the comet's heart could also implode.</strong> If the comet's material vaporizes in quite the right way, it could speed up the comet's spin so dramatically that the iceball flies to pieces.</p>
</blockquote>
<p>I understand that the gist of this is that the comet's absolute magnitude is not increasing in a typical way as it gets closer to and is increasingly warmed by it, and may actually be decreasing.</p>
<p>But where might these absolute magnitude measurements have been coming from? Are they photometric? Were they systematic from one or a few well-characterized instruments? Was there a campaign to track it by experienced amateurs?</p>
<p><strong>Question:</strong> What observational data was there that comet Leonard C/2021 A1 might have been dimming and/or breaking up?</p>
<hr />
<p>For reference, the quotes in the Space.com article are attributed to University of Maryland astronomer Ye Quanzhi <a href="http://yeqzids.github.io/" rel="nofollow noreferrer">http://yeqzids.github.io/</a> but we don't know how well they have been maintained in context.</p>
<p>They've also <a href="https://twitter.com/aciqra/status/1465069604489678850" rel="nofollow noreferrer">retweeted this</a>:</p>
<blockquote>
<p>Comet C/2021 A1 (Leonard) looking a bit deflated this morning; its flattened gas coma suggests the nucleus is likely fragmenting at some level. While still brightening as seen from Earth, the absolute brightness of its dust coma has actually faded ~0.4 mag over the past week.</p>
</blockquote>
<p>It seems that same instrument has been used for some pretty nice looking amateur photometry, it's possible that this instrument (<a href="https://youtu.be/Gmq4WIjQxp0" rel="nofollow noreferrer">in sunny Southern California</a>: <a href="https://near.earth/qz/" rel="nofollow noreferrer">https://near.earth/qz/</a>) is the source of the systematic photometry, but I don't know.</p>
<ul>
<li><a href="https://twitter.com/aciqra/status/1451430558253269000" rel="nofollow noreferrer">https://twitter.com/aciqra/status/1451430558253269000</a></li>
<li><a href="https://twitter.com/aciqra/status/1212513733282418688" rel="nofollow noreferrer">https://twitter.com/aciqra/status/1212513733282418688</a></li>
</ul>
<p>More about recent cometary breakups:</p>
<ul>
<li><a href="https://arxiv.org/abs/2105.02269" rel="nofollow noreferrer">Disintegration of Long-Period Comet C/2019 Y4 (ATLAS): I. Hubble Space Telescope Observations</a></li>
</ul>

CC BY-SA 4.0
2021-12-20T19:17:32.457Z
Not an answer because it's not definitive, but the quoted astronomer, Ye Quanzhi, did publish a paper in October 2021 about this comment and mentioned using the Lowell Observatory and Palomar Hale Telescopes. Very possibly he used the same telescopes for later observations. Ref. [Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus](https://iopscience.iop.org/article/10.3847/1538-3881/ac19ba/pdf)
zephyr
CC BY-SA 4.0
2022-01-07T22:38:46.137Z
@zephyr I don't think this question will be getting much more attention; please feel free to post a "too long to be a comment" answer which I can accept, idea being that it's a good enough answer and it ever-so-slightly helps the site statistics.
uhoh
<observational-astronomy><amateur-observing><comets><photometry>
What observational data was there that comet Leonard C/2021 A1 might have been dimming and/or breaking up?
uhoh
# What observational data was there that comet Leonard C/2021 A1 might have been dimming and/or breaking up?

(Asked by: username_0 on 2021-12-10)

Space.com's [Comet Leonard, the brightest of the year, is fading and acting strange](https://www.space.com/comet-leonard-fading-maybe-splitting) seems to be full of inexact language, like "something's wrong" and "unhealthy" and "goner" and "the comet's heart could also implode":

> "It's not great news. The comet should be brighter and brighter," Quanzhi Ye, an astronomer at the University of Maryland who specializes in comets, told Space.com. "If it's not getting brighter then **something's wrong**, but we don't know exactly what at this stage."

> "Why it's fading, there are all kinds of hypotheses," Ye said. "The simplest and the most obvious one is **something unhealthy is happening** to the comet."

> There are several factors that could break apart a comet, Ye noted. The gravitational tug of the sun or a large planet could pull it apart, sure, **but the comet's heart could also implode.** If the comet's material vaporizes in quite the right way, it could speed up the comet's spin so dramatically that the iceball flies to pieces.

I understand that the gist of this is that the comet's absolute magnitude is not increasing in a typical way as it gets closer to and is increasingly warmed by it, and may actually be decreasing.

But where might these absolute magnitude measurements have been coming from? Are they photometric? Were they systematic from one or a few well-characterized instruments? Was there a campaign to track it by experienced amateurs?

**Question:** What observational data was there that comet Leonard C/2021 A1 might have been dimming and/or breaking up?

---

For reference, the quotes in the Space.com article are attributed to University of Maryland astronomer Ye Quanzhi <http://yeqzids.github.io/> but we don't know how well they have been maintained in context.

They've also [retweeted this](https://twitter.com/aciqra/status/1465069604489678850):

> Comet C/2021 A1 (Leonard) looking a bit deflated this morning; its flattened gas coma suggests the nucleus is likely fragmenting at some level. While still brightening as seen from Earth, the absolute brightness of its dust coma has actually faded ~0.4 mag over the past week.

It seems that same instrument has been used for some pretty nice looking amateur photometry, it's possible that this instrument ([in sunny Southern California](https://youtu.be/Gmq4WIjQxp0): <https://near.earth/qz/>) is the source of the systematic photometry, but I don't know.

* <https://twitter.com/aciqra/status/1451430558253269000>
* <https://twitter.com/aciqra/status/1212513733282418688>

More about recent cometary breakups:

* [Disintegration of Long-Period Comet C/2019 Y4 (ATLAS): I. Hubble Space Telescope Observations](https://arxiv.org/abs/2105.02269)

**Tags:** observational-astronomy, amateur-observing, comets, photometry

> **Comments:**
> **username_1**: Not an answer because it's not definitive, but the quoted astronomer, Ye Quanzhi, did publish a paper in October 2021 about this comment and mentioned using the Lowell Observatory and Palomar Hale Telescopes. Very possibly he used the same telescopes for later observations. Ref. [Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus](https://iopscience.iop.org/article/10.3847/1538-3881/ac19ba/pdf)  
> **username_0**: @username_1 I don't think this question will be getting much more attention; please feel free to post a "too long to be a comment" answer which I can accept, idea being that it's a good enough answer and it ever-so-slightly helps the site statistics.  

---

## 0 answers

