In the Old Testament, a new month was marked by a new moon. We celebrate the New Moon as a monthly time of renewal. The word "new" in Hebrew is the word chodesh, from the root word chadash, which means "to renew." We really don't see a "new" moon each month ~ we see a "renewed" moon.
"And it shall be from new moon to new moon And from sabbath to sabbath, All mankind will come to bow down before Me," says YHVH. Isaiah 66:23Rosh Chodesh Sameach! (Happy New Moon!)