The septagram is a seven-pointed star, a symbol of synthesis and mystery due to its links with the number seven. Seven is an integrating number, encapsulating as it does the hierarchical orders of classical mystical thought. There are seven planetary spheres governed by the seven planets of classical astrology, seven colors in the rainbow, seven days of the week and seven distinct notes in a diatonic musical scale.
The number three relates to Heaven and the higher realms, not just through the concept of trinity but also as the vertical axis of three-dimensional space; and the number four pertains to the Earth and manifest realms, partly through its relation to the square and the four directions of two-dimensional space. Seven and the septagram can thus be considered as representing the sum of Heaven and Earth, and they allude to the seven directions of space - two directions for each dimension plus the center. As an aside, twelve, the number of signs in the zodiac, is a number of totality, expressing the multiplicative possibilities of Heaven and Earth as well as Heaven in a new mode (12 and 3 are numerologically equivalent, as 1 + 2 = 3).
http://www.byzant.com/Mystical/Symbols/Septagram.aspx
also looks like a wheel to me