Astronomy, telescopes and enchanted ceilings

[Catlady (Rita Prince Winston)]

Thanks to Shaun for an indisputable answer to my question.

Kaitlin wrote in
http://groups.yahoo.com/group/the_old_crowd/message/1945 :

<< Is it the same conditions as outside, or do the maintenance
people/elves decide what weather the ceiling should have? >>

The ceiling matched the weather outside. SS: "Harry looked upward and
saw a velvety black ceiling dotted with stars. He heard Hermione
whisper, "Its bewitched to look like the sky outside. I read about it
in Hogwarts, A History." It was hard to believe there was a ceiling
there at all, and that the Great Hall didn't simply open on to the
heavens."

CoS: "the bewitched ceiling, which always mirrored the sky outside" 

Once upon a time, there was a dedicated HPfGU poster named Nick, who
took a day trip to Chepstow specifically to violate the 'Danger: Keep
Out' signs by poking around the ruins of Chepstow castle, as Jo and Di
had as children. He posted that this investigation had confirmed his
belief that Chepstow castle was the model for Hogwarts castle, and
that the roofless Great Hall of the ruin had inspired the idea of the
enchanted ceiling that always looks like the sky above.

Pippin wrote in http://groups.yahoo.com/group/the_
old_crowd/message/1949 :

<< I think even magical telescopes are probably delicate things
that wouldn't take well to being constantly moved aside to make way
for the tables, or being exposed to the grease and steam of food
service. >>

The list in SS of things that students are required to bring to
Hogwarts includes 'telescope set' (between 'glass or crystal phials'
and 'brass scales'). 

"Hagrid wouldn't let Harry buy a solid gold cauldron, either ("It says
pewter on yer list"), but they got a nice set of scales for weighing
potion ingredients and a collapsible brass telescope." 

"They had to study the night skies through their telescopes every
Wednesday at midnight and learn the names of different stars and the
movements of the planets."

As it says 'their telescopes', I assume they're using the ones they
bought in Diagon Alley, really spyglasses rather than telescopes, but
whose 'collapsible' way of folding up created the verb 'to telescope'
for things (other than Freudian references) that get longer or
shorter.