Happy Birthday, Moon by Frank Asch, 1982.

Bear really loves the moon and decides that he would like to give the moon a birthday present.  The problem is that he doesn’t know when the moon’s birthday is.  He tries asking it, but it doesn’t answer.

Deciding that he needs to get closer to the moon to talk to it, Bear goes to the mountains to ask the moon when its birthday is.  In the mountain, Bear hears his own echo and thinks that it is the moon answering him.  When Bear tells the moon that his birthday is tomorrow, the “moon” replies that its birthday is tomorrow.  Bear is pleased, especially when the moon echoes his wish for a hat for its birthday.

Bear buys the moon a hat and puts it on top of the moon by putting it in a tree.  The following morning, the hat is on Bear’s doorstep, and Bear accepts it as the moon’s present to him.

When the wind blows poor Bear’s hat away, Bear goes to the mountains again to apologize to the moon for losing the hat.  It’s okay, though, because Bear and the moon still love each other.

Bear never realizes that what he’s hearing is his own echo.  It’s sweet although somewhat silly.  If you wonder what happened to the hat in the end, it’s shown on the back cover of the book, holding a bird’s nest.

The book is currently available online through Internet Archive. (When you borrow a book from Internet Archive, you have to set up an account, but it’s free.)