In ancient times, astrology and the zodiac were used as a symbolic representation of the human being's microcosmos The reason why there are 12 zodiac signs, is because each sign represents one of the twelve fundamental forces working in the microcosmos.
To every sign on the zodiac 30 degees of the zodiacal circle were assigned, which were divided into groups of 10 degrees. To every group of ten, another constellation outside the zodiac was linked. This gives a total of 12 + 3 * 12 = 48. So in those times, there were only 48 constellations , while there are more now, and a lot of visible stars were not part of any constellation. This was because the constellations mainly served a symbolic purpose in connection to the theories on the microcosmos, rahter than help create some kind of random order in the galaxy.
The Sun was one of the most important bodies in astrology. Added up to the afore mentioned 48, we get 49. This is the product of seven and 7, i.e. the holy number squared. Seven is the number of main chakras, the points of psychic energy in the human body. (see also The Seven Chakras)
Of course modern day pop-astrology has got nothing to do with all this.