This is the case for Hathor and Nut, both considered sky goddesses by the Egyptians. In later times, Hathor subsumes much of Nut's imagery and function, as well as adding features from other Goddesses from elsewhere (such as the conflation of Hathor and the Greek Aphrodite, based on Hathor being the most similar figure the Greeks could find to the Goddesses they knew). Both Goddesses are extremely ancient in the history of Egypt, but they originally served quite distinct functions.
First, let's look at Nut. She is the image of the starry night sky, spread over the Two Lands, represented by her brother/husband Geb. Their father, Shu, holds them apart, creating the space (Air) within which life can manifest. All of this results from Atum-Re's direction in the process of creating the world in which everyone lives, and is part of the mythic creation cycle of Iunu, the center of Re's and the Ennead's cults.
Nut also plays an even earlier part in creation myth as part of Tehuti's Ogdoad, a group of paired male/female beings who shape the "ether" to create the universe. Nut is the companion of Nu, the primeval waters, and is essentially "Shakti" to his "Shiva" in this mythic cycle. That's why her hieroglyph includes three jagged lines, the symbol for water. Her determinative symbol is a water pot, which some equate to the feminine womb, from which the Sun God emerges each morning.
In either case, Nut represents the vastness of space, in which all of creation can manifest. I see her function in the Ogdoad as starless, black, and empty night, corresponding to the infinitely deep, dark waters of her partner, Nu. Both serve as the ground against which the other three pairs in the Ogdoad generate the Egg of Creation, which Tehuti calls into existence through the great Word (Heka aa).
Once the Egg has born fruit through the raising of the mound within the midst of Nu's waters, Atum-Re can manifest and begin generating the next cycle of creation. I believe that when he draws Nut into companionship with Geb as his grandchildren, this is when she gets her stars to distinguish her from the consort of Nu. Geb, as the Earth floating in space, still resided on the waters of Nu, and within the embrace of Nut; the concept of infinity is not lost. But the stars represent the disembodied souls of potential life on Earth; remember that the Egyptians believed that when we die, we travel back into Nut's starry void if our hearts are true.
So, Nut's principal resonance, if you will, is with infinite, deep space. She defines the boundaries of life on Earth, which exists within the thin atmosphere provided by Shu. We come from her, and we return to her, embodying the esoteric principle of incarnation and life cycles.
Hathor, on the other hand, has a much more specific association with the sky. This is clear from her hieroglyphic name, Hwt hr, meaning "house of Horus." Hathor is described as a daughter of Re, and is part of a triple Goddess form with Bast and Sekhmet, which I've described elsewhere. Horus becomes conflated with Re as the Sun God as Ruler, embodying the principle of "as above, so below" through the pharaohs. ("Pharaoh" is actually "Per aa," or "Great House," meaning the chief house of the God on Earth.)
|The Lion Gates of Morning|
As the Sun Boat progresses through the House of Horus over the course of the day, Re ages, from Khepera-Re in the morning, to Re-Heru at mid-day, to the enfeebled, old Atum-Re at evening. Again, the setting point of the Sun on the western horizon is significant, and Hathor plays a key role in the Sun's journey here. Hathor of the Western Horizon is named "Hwt hr Khentimentiu," Hathor of the doors to the otherworld. Like the morning point, these doors/gates open to take in the corpse of the old Sun God as he dies, with his blood staining the western sky red; once he has passed through, he becomes Amun-Re, the Hidden God.
This is why the west bank of the Nile was considered the appropriate land of the dead, as it coincided with Re's daily death and descent into the otherworld.
Once again, in the Book of the Pylons, Hathor and Bast serve Re's journey through the Dwt each night, when he must contend with the forces of chaos (Apep) that want to prevent the next day's dawning. Re comes to the Hall of the Double Ma'ati for judgment, just as people were believed to come after death, and the day's events and quality are evaluated before Osiris. This is where Tehuti records the history of the Day's events in the eternal record, which covers everything that Re has seen during the course of the day. Clearly, when an individual dies and comes to the Hall of Judgment, Tehuti is ready with the scroll recording all that Re has seen, and thus knows the truth of the individual's behavior as he/she speaks before Osiris.
I believe that the version of the Prt-m-hru (Book of Coming Forth by Day) that deals with this underworld journey and judgment of the dead individual parallels Re's journey, and that having one's heart eaten by Iammit signifies being cast back into incarnation to try again to "get it right." The Egyptians envisioned the Dwt for the justified dead to be so much like all of the things they loved during life that I cannot accept they did not see the connection with reincarnation for those who didn't "get it right the first time." Perhaps I should refer to this as the "Law of Conservation of Souls."
Those who stand before Osiris whose hearts balance in the scales against the feather of Ma'at are said to be "true of voice, justified." They travel onward to become reborn as stars in the body of Nut; in other words to be resorbed into the infinite Ground of Being from which they originally came. Whether they choose to be reborn in Earthly incarnation at that point is anyone's guess, but as Nut becomes reborn as the granddaughter of Re to serve as the Sky above the Earth, I suspect there was a mechanism whereby a justified soul could return to incarnation for new lessons.
Obviously, I can't prove any of this, as it depends on a very alternative reading of the Book of the Dead, The Book of the Pylons, and the Book of Gates, among others; however, given the way in which the Egyptians envisioned the organizing force of Ma'at, and the replication of everything at each level of being, it makes an attractive amount of sense, at least to me.
The different myths of the Egyptians are not meant to be taken as separate, unrelated sequences, but as a rich, overlapping tapestry unfolding in many different layers of meaning. It is definitely not the way that Western linear, logical, rational mental processes prefer, but accords well with the concept of Ma'at that lies at the heart of all Egyptian religion and philosophy. We just have to let their magic words (hekau, hieroglyphs) tell us how they conceived of their world, rather than trying to filter it through our own concepts.