also called a Horned Cross
The Lunate Cross is usually either used as a heraldic symbol, when it is also called a Croissant, or as a Neopagan symbol, when it is also called a Moon Cross. (Generally with symbols, the moon is shown as a crescent and the sun is shown as a circle. )
When the Christian crusaders conquered the Turks they took the crescent, the symbol of Islam, back to western Europe as a war trophy and incorporated it into their insignia. It has appeared in several coats-of-arms since the reign of King Henry III.
"Imaculada" (by Murillo)
The Virgin Mary with a white crescent moon at her feet
(Click image to enlarge)
In Christianity, the crescent moon can represent virginity, and in particular, the Virgin Mary, Mother of God. (See Crescent Cross.) The set of four crescents, forming a Lunate Cross, has in itself no additional Christian significance, although it can be viewed as a cross with four stylized Tau patterns.
The Lunate Cross is also a Neopagan symbol, purportedly used by northern European shamans. The concave shape of the moon represents our hidden feminine nature with its various moods. Being a controller of the tides, having a moon in four directions can help balance our moods.
Neopagans have also told us that an aging goddess is the polarity of the universe and the crescent moon is a symbol of this goddess. We are not sure what the 'polarity of the universe' actually means, but it's comforting to know it is feminine.
The moon 'horns' are outward-facing, protecting the cross from evil which might approach from any direction. There are four moons to remind us that the moon has four phases, symbolising protection throughout the month.
And this is all rather difficult for Christians to reconcile with, because the Cross is the antidote for evil. It needs no protection from evil, and even if it did, it's unlikely that the moon could provide this. (See also why we don't trust astrology.)
Have you ever wondered why, when there's a total solar eclipse, the sun and moon appear to be exactly the same size? The entire universe is just right for life on Earth, and the eclipse of our most familiar neighbours fit so perfectly that we can only see tiny bits of sunlight streaming through the rugged valleys on the moon's surface, creating the beautiful and striking diamond ring effect.
This is all due to an amazing coincidence. The sun is about 400 times as wide as the moon, but it is also 400 times further away. The two therefore look the same size in the sky – a unique situation among our solar system's eight planets and 166 known moons.
Why is that?
We know that the moon is very slowly moving away from earth (about 3.8 cm per year) and this total solar eclipse phenomenon will not exist in the future. So why now? Why do we happen to live in the relatively brief period of earth's history when our moon almost perfectly blocks the sun?
Could it be that God has given us this optical illusion for one simple reason; to get us to consider the possibility that it is all part of some Grand Scheme? No? Then what other reason could there be? The odds of it being pure 'chance', a random fluke, are astronomical.
See other Crescent Crosses
The sun and other major bodies in the solar system are oblate spheroids. The moon is shaped like an egg, but we see it as round because the big end points towards us.