Fixed Stars aspects:
Fixed star aspects represent a challenge for composite and comparison charts. Which epoch should be used? Consider that if two natal charts of very different years of birth are used to construct a composite chart how do we decide which year (epoch) to use to calculate the fixed star aspects? The composite chart has no year of birth, nor a day of birth or a place of birth. It is entirely astronomically artificial. So what to do?
The epoch used is taken from the first named natal chart date. If the difference in years between the two natal charts is insignificant, possibly less than 50 years, the aspects will be accurate enough. For instance in the composite chart of Queen Victoria and Prince Albert they were both born on 1819. The fixed stars calculation can use the 1819 date as the epoch without any concern as to relevance and accuracy. This also applies to comparison synastry charts.