Here's what happens in the registry (concerning cel links) when celestia is installed on windows machine (if option for cel links is checked): 

<p>
<ol>
<li>CreateKey HKCR\cel (create new key in HKEY_Classes_Root named cel)</li>

<li>SetValueEx HKCR\cel "URL:Cel Protocol" (set default string value for this key to URL:Cel Protocol) </li>

<li>SetValueEx HKCR\cel\URL Protocol "" (create new string value named URL Protocol and set to null) </li>

<li>Createkey HKCR\cel\Shell (create new key under Cel) </li>

<li>SetValueEx HKCR\cel\Shell "" (set default string value to null) </li>

<li>Createkey HKCR\cel\Shell\open (create new key under Shell) </li>

<li>SetValueEx HKCR\cel\Shell\open "" (set default string value to null) </li>

<li>Createkey HKCR\cel\Shell\open\Command (create new key under open) </li>

<li>SetValueEx HKCR\cel\Shell\open\Command "C:\Program Files\Celestia\celestia.exe --once --dir "C:\Program Files\Celestia" -u "%1"" (set default string value to C:\Program Files\Celestia\celestia.exe --once --dir "C:\Program Files\Celestia" -u "%1") </li>

</ol>

<p>Note: Omitted Closekeys and Querykeys for readability. 

<p>So what you end up with in your registry is: <br>
<img src="regmap.jpg" />