Augustine (and many others) have asked “why the particular creations of each day?” For example, why were the sun and moon created on the fourth day?
For centuries - probably preceding even the New Testament - people studying the Old Testament noted that the first three days of creation report God creating habitations, and the second three days of creation report God creating inhabitants. The inhabitants (sun, moon, and stars) created on the fourth day were placed in homes created on the first day (day and night). The inhabitants created on the fifth day (birds and fish) were placed in homes created on the second day (sky and seas). Finally, the inhabitants created on the sixth day (land animals, and humans) were placed on land, which was created on the third day.
By the way, the answers given by the early church fathers seem, to me, much more astute than the answers you would find from contemporary proponents of reading Genesis 1 as historical science.
Creation and Genesis (Catholic Answers) quotes from many Church Fathers, including St. Augustine.