Frogsnack
Well- people at least knew which stars would be in the sky on the night of his birth!
Perhaps God gave them the revelation to look for it. The same star was on the sky to see for everyone, but only a handful of people knew what the star pointed to.
Perhaps they had read this prophecy or had been told about this prophecy by Daniel?
I shall see Him, but not now: I shall behold Him, but not nigh: there shall come a Star out of Jacob, and a Sceptre shall rise out of Israel, and shall smite the corners of Moab, and destroy all the children of Sheth, and Edom shall be a possession. Seir also shall be a possession for his enemies; and Israel shall do valiantly. Out of Jacob shall come He that shall have dominion, and shall destroy him that remaineth of the city (Numbers 24:17_19).
I think we can see with Herod's reaction to the Magi's news that it came as a surprise.
Matthew 2:1-6
The Magi Visit the Messiah
2 After Jesus was born in Bethlehem in Judea, during the time of King Herod, Magi from the east came to Jerusalem 2 and asked, “Where is the one who has been born king of the Jews? We saw his star when it rose and have come to worship him.”
3 When King Herod heard this he was disturbed, and all Jerusalem with him. 4 When he had called together all the people’s chief priests and teachers of the law, he asked them where the Messiah was to be born. 5 “In Bethlehem in Judea,” they replied, “for this is what the prophet has written:
6 “‘But you, Bethlehem, in the land of Judah,
are by no means least among the rulers of Judah;
for out of you will come a ruler
who will shepherd my people Israel.’”