Invisibility cloaks and Aurors (was Invisibility Cloak/Sirius)

[kiricat2001]

No: HPFGUIDX 70034

--- In HPforGrownups at yahoogroups.com, "kadede" <kadede at s...> wrote:
> Diana wrote:
> 
>   > Why couldn't have Sirius also used the cloak not only to help 
the
>   > order but to keep an eye on Harry?  He wouldn't have been seen 
by
>   > anyone and yet he would of felt as if he was doing something
>   > important for the Order.  I don't know, just a thought.


> Ravenclaw Black:

> 
> Invisibility cloaks are useless when aurors (and maybe others) are 
around
> (Mad Eye Moody saw through it in GoF, so does Dumbledore in 
Hagrid's hut in
> CoS). As not all aurors are in the Order of the Phoenix (yet), 
Sirius could
> be quickly caught.

Is that true?  Can all Aurors see through invisibility cloaks? Or 
does Moody have that ability due to his magical eye?  IIRC, I don't 
think Dumbledore gives any explanation as to why he has this 
particular talent.  Certainly, if all Aurors can do this, it would 
limit the defense a cloak could have given Sirius.  But, didn't some 
of the OoP people use the cloak to be able to hang around the Dept. 
of Mysteries unnoticed while they were guarding the prophecy?  
Wouldn't they have run the risk of being detected by whatever Aurors 
were floating around the building?

And, how common are these cloaks anyway? 
 
Marianne