One of the most ubiquitious elements of Snow White and the Seven Dwarfs is the magic mirror. Most of us know some version of "Mirror, Mirror on the wall, who's the fairest of them all?" It is such a popular part of the tale that it is hard to imagine Snow White's wicked stepmother without it. There has even been an entire novel devoted to the mirror, Mira, Mirror by Mette Ivie Harrison.
However, there are no mirrors in many Snow White variants. In some, the older woman has no magic informer but relies on people, such as servants or visitors to her inn, to tell her she is the most beautiful. This is common in several of the Innkeeper variants of the tale from southern Europe. When the daughter grows older and the answer changes, the woman is jealous and orders her daughter's death.
Perhaps the most common substitute for the mirror is a rather wonderfully logical object: the Sun. Many Snow White variants have the mother, stepmother, sisters, etc. asking the Sun who is the most beautiful.
For example, in "Marietta and the Witch, Her Stepmother" from Greece, we read:
“My great and beautiful Sun! You who go around the world, tell me: Have you seen a woman more beautiful than me?”
“I am beautiful, you are beautiful,” replied the Sun, “but not as beautiful as Marietta.”
In most of these variants the implication is that the Sun is all-seeing and all-knowing thanks to its daily travels so it can best tell who is the most beautiful person in the world. The Sun never gives advice on how to destroy the beautiful daughter, it is quite simply logical and truthful in its answers. Thus it betrays the Snow White character over and over again as she survives each murder attempt and even explains where she is living.
It's rather ingenious and even overcomes the questions over technology and availability of mirrors in past times. Perhaps the real question is which came first, the mirror or the Sun?
And, once again, you can read many tales with the Sun replacing the mirror in Sleeping Beauties: Sleeping Beauty and Snow White Tales From Around the World.