I'm seeing a lot of deeply unscientific arguments in these comments. This "Cult of Science" mentality is a concerning trend, where instead of thinking rationally and scientifically about something, people blindly follow whatever the contemporary consensus is. Your friends using poor methodology is not a rational argument against a field, any more than solving a math problem incorrectly invalidates math.
For what feels like the tenth time: I don't believe any star (other than the sun) has any direct significant effect on a person. However, correlation isn't causation. I do believe that it is possible that there might be other factors which vary over the course of the year which may have some effect, and that those variations can be coincidentally correlated to the zodiac phases as a convenient reference.