Revelation 21:10

10  And he carried me away in the spirit to a great and high mountain, and shewed me that great city, the holy Jerusalem, descending out of heaven from God,

John is carried in the spirit to a great and high mountain he could have even been taken to the moon. He was probably somewhere in space so he could get an unobstructed view of this city coming out of the second or third heaven toward the earth. The Holy City will be an awesome thing to see. It does not say the holy city will actually touch the earth. It might just remain in orbit. From the earth, it may look like a jeweled moon in the sky. It may cast different colors and light shows on the earth from the light within her and from the light reflected or refracted from the sun and moon through her twelve foundational colors that are studded with all types of precious stones.