Norman Lockyer (1836-1920) was a respected astronomer whose ideas have had a profound effect on archaeoastronomy yet his observations and theories concerning relationships between ancient ritual sites and astronomy were discounted and ridiculed.
In the 1960's & 70's, Professor Alexander Thom and Gerald S. Hawkins were notable for publishing revolutionary works claiming that megalithic monuments were used for accurate solar and lunar measurements. At the time there was much enthusiasm for these ideas but also much resistance. Popular culture continues to find that many of these monuments are indicators of particular solar or lunar events but considerable academic opposition remains due to a perceived lack of evidence.
Whole Horizon Analytical Techniques clearly demonstrate that these Ancient Sacred Places were accurately tuned to cycles of sun and moon. It also shows that built alignments were actually secondary features. Place came first. Understanding the context of place gives meaning to the architecture of individual sites. It also aids understanding of time sequencing of complex sites.
Prehistoric people were not so much interested in marking single events as in measuring time periods. Looking at the whole picture in fact by finding places where there was an all round fit between earth and sky. Immersed in natural reality to a degree that is hard to imagine today, they developed a sophisticated luni-solar calendrical system of considerable accuracy. Being observational, it was entirely self-correcting but, in the end, was probably killed off by climatic deterioration at the end of the Bronze Age.
By seeing the landscape and how it changes whilst moving within it, they found places where the shape of the horizon fitted the patterns in the sky. This enabled them to measure both the annual solar and the 18.6 year lunar nodal cycles with considerable accuracy. Thus they could predict eclipses. By 4000 BCE certainly but probably earlier. That's a minimum of 3000 years before the Mesopotamian astronomers who are generally credited with being the earliest to do so. Amazing knowledge and skill that continued right through the megalithic period, from the earliest Irish stone tombs, to the end of the Bronze Age.
Every monument was built in a place that was a good observing position. Even within "cemetery" or "complex" situations, each individual monument has specific observational reasons for being exactly where it is.
What they did is actually very clever and if you want to do more than take my word for it then you'll need to be familiar with some terminology and some astronomy. The necessary information is provided but it will help a lot if you also get out there to watch the sky and play with your perception of the landscape.