The lunar chart is specific for you, as it depends on your time and place of birth, etc, so don't worry about the star signs. The lunar fertility chart can be quite different to your menstrual chart, but they often align at times during the course of the year. From what I have read, you are most fertile if both your menstrual ovulation time and lunar peak time coincide (most fertile is not the same as guaranteeing the gender though). The next most fertile time is when your lunar peak is during menstruation, but of course not everyone is keen to BD then. The Odan Institute website says to maximise the success of predicting a girl, you should keep a chart. Mark day 1 as your first day of menstrual cycle. Mark day 9-18 on your chart as 'periodic days'. They say if your lunar peak occurs during this time your success rates are 87% for achieving the predicted gender. If your lunar peak falls outside these days and you get pg, they say the success of achieving the predicted gender is 100%. Personally I am not going to rely on it entirely, but try and include it along with diet and other tips I have got from in-gender.
With the lunar chart you are supposed to BD 24 hours before your lunar peak day and then ideally 12 hrs later. Apparently BD 24 hrs before is what can trigger the lunar ovulation. You do not BD after the date of your fertile peak. The Odan Institute gives you specific times to stick between. I am not trying to promote the Odan Institute in terms of buying one of their charts, as it costs money, but their website does have lots of FAQ which may help answer your questions.
By the way, the UK is in the Northern Hemisphere. 
GL with all the info out there. It can get a bit confusing can't it!