Magic is all about work of energies, peoples do their spells & rituals at some specific time/day because to have use and effect of other energies too, we know the power of the moon and planets, we all have a system with the power of universe and all its creations.
Talking about astrology, it's all about the day you were borned, which gives you your star/sun sign and sometimes the time & place too effects, as well as your name too, all this makes your legacy, and so you get your kundali, horoscopes, numerology... But again there are many who don't believe this like me, you yourself are the way to life, life is destined how you live.
The powers of the moon and planets do are very real, we know it from many centuries the power of moon and of each and every planet & its effects, Yes, magick comes from within, you must think that it's just channeling of Power of moon or any specific planet, eg: one may use the Venus while in a love spell as Venus holds power of love, lust.. Etc..