The_Complete_Chronicles_of_Narnia_(volumes_1-7,_in_order_of_publication)

After that it was all nouns and verbs till lunchtime, but I don't think Caspian learned
much. He was too excited. He felt sure that Doctor Cornelius would not have said so
much unless he meant to tell him more sooner or later.
In this he was not disappointed. A few days later his Tutor said, "Tonight I am going to
give you a lesson in Astronomy. At dead of night two noble planets, Tarva and Alambil,
will pass within one degree of each other. Such a conjunction has not occurred for two
hundred years, and your Highness will not live to see it again. It will be best if you go to
bed a little earlier than usual. When the time of the conjunction draws near I will come
and wake you."
This didn't seem to have anything to do with Old Narnia, which was what Caspian really
wanted to hear about, but getting up in the middle of the night is always interesting and
he was moderately pleased. When he went to bed that night, he thought at first that he
would not be able to sleep; but he soon dropped off and it seemed only a few minutes
before he felt someone gently shaking him.
He sat up in bed and saw that the room was full of moonlight. Doctor Cornelius, muffled
in a hooded robe and holding a small lamp in his hand, stood by the bedside.
Caspian remembered at once what they were going to do. He got up and put on some
clothes. Athough it was a summer night he felt colder than he had expected and was quite
glad when the Doctor wrapped him in a robe like his own and gave him a pair of warm,
soft buskins for his feet. A moment later, both muffled so that they could hardly be seen
in the dark corridors, and both shod so that they made almost no noise, master and pupil
left the room.
Caspian followed the Doctor through many passages and up several staircases, and at
last, through a little door in a turret, they came out upon the leads. On one side were the
battlements, on the other a steep roof; below them, all shadowy and shimmery, the castle
gardens; above them, stars and moon. Presently they came to another door, which led into
the great central tower of the whole castle: Doctor Cornelius unlocked it and they began
to climb the dark winding stair of the tower. Caspian was becoming excited; he had never
been allowed up this stair before.
It was long and steep, but when they came out on the roof of the tower and Caspian had
got his breath, he felt that it had been well worth it. Away on his right he could see, rather
indistinctly, the Western Mountains. On his left was the gleam of the Great River, and
everything was so quiet that he could hear the sound of the waterfall at Beaversdam, a
mile away. There was no difficulty in picking out the two stars they had come to see.
They hung rather low in the southern sky, almost as bright as two little moons and very
close together.
"Are they going to have a collision?" he asked in an awestruck voice.