<p>SWAN seems to be on a parabolic orbit. This means that it is the first time that it is interacting with the Sun, making it a "new" comet. New comets are covered in a layer of very volatile elements that will vaporize pretty fast when the comet is still far away from the Sun. This causes a surge in brightness. But once those very volatile elements are gone, it stops getting brighter and the comet's brightness can even decrease. </p>

<p>In addition to this, it is mostly losing gas, so its tail isn't as visible as if it were a tail of dust.</p>

<p>(From <a href="https://www.cieletespace.fr/actualites/la-comete-swan-mantient-le-suspens-pour-les-prochains-jours" rel="nofollow noreferrer">this article</a>, in French)</p>

CC BY-SA 4.0
2020-05-21T18:02:38.243Z
2020-05-25T07:49:32.847Z
2020-05-25T07:49:32.847Z
usernumber
<p>The SWAN C/2020 F8 comet is passing near the Earth, but <a href="https://en.wikipedia.org/wiki/C/2020_F8_(SWAN)#cite_note-COBS-3" rel="nofollow noreferrer">from Wikipedia</a></p>
<blockquote>
<p>The comet has dimmed a small amount since May 3.</p>
<p>It was expected to possibly reach 3rd magnitude in May, but is now expected to hover closer to magnitude 5.</p>
</blockquote>
<p><a href="https://i.sstatic.net/WosQ7.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/WosQ7.png" alt="enter image description here" /></a></p>
<p>What is the cause of this dimming?</p>

CC BY-SA 4.0
2020-05-18T11:01:05.373Z
you may be able to answer [How is Comet SWAN C/2020 F8 doing? Will it become easily visible by eye?](https://astronomy.stackexchange.com/q/36218/7982) in which case I can accept it rather than have two related unanswered questions. This seems like the more interesting one of the two.
uhoh
<observational-astronomy><comets><magnitude>
Why is SWAN dimming?
usernumber
# Why is SWAN dimming?

(Asked by: username_0 on 2020-05-18)

The SWAN C/2020 F8 comet is passing near the Earth, but [from Wikipedia](https://en.wikipedia.org/wiki/C/2020_F8_(SWAN)#cite_note-COBS-3)

> The comet has dimmed a small amount since May 3.
>
> It was expected to possibly reach 3rd magnitude in May, but is now expected to hover closer to magnitude 5.

[![enter image description here](https://i.sstatic.net/WosQ7.png)](https://i.sstatic.net/WosQ7.png)

What is the cause of this dimming?

**Tags:** observational-astronomy, comets, magnitude

> **Comments:**
> **username_1**: you may be able to answer [How is Comet SWAN C/2020 F8 doing? Will it become easily visible by eye?](https://astronomy.stackexchange.com/q/36218/7982) in which case I can accept it rather than have two related unanswered questions. This seems like the more interesting one of the two.  

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## 1 answers

### Answer by username_0 on 2020-05-21. Score: 1 | Accepted answer

SWAN seems to be on a parabolic orbit. This means that it is the first time that it is interacting with the Sun, making it a "new" comet. New comets are covered in a layer of very volatile elements that will vaporize pretty fast when the comet is still far away from the Sun. This causes a surge in brightness. But once those very volatile elements are gone, it stops getting brighter and the comet's brightness can even decrease.

In addition to this, it is mostly losing gas, so its tail isn't as visible as if it were a tail of dust.

(From [this article](https://www.cieletespace.fr/actualites/la-comete-swan-mantient-le-suspens-pour-les-prochains-jours), in French)


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