The research, which resulted in the creation of this book, started about fifteen years ago. Then, taking building upon my basic expertise (as neurologist and psychiatrist) I was interested in mythology, following the teachings of Carl Gustav Jung. I was researching the mythology of the South Slavs, translating some Norse and Celtic myths into Serbian and carefully rereading the Greek ones... The turning point happened in 2009, which was declared the year dedicated to Astronomy in Culture. The media has been abuzz with reports of various circular formations around the world, with growing evidence that these were deliberately created sky-watching sites. At that time, Astronomy in culture was still a new science, still building its methodology. The world was almost flooded with information about Stonehenge or the circle near the village named Goseck in Germany, as places deliberately created for certain individuals to observe the apparent movement of the Sun. That piqued my curiosity. The Sun was an important deity in several known mythological systems. Astronomy in culture offered a link between Anthropology, Archaeology and Astronomy. Suddenly, there was something that could be called the Anthropology of Astronomy, and it was all very inspiring. I started to flip through satellite maps, looking for circular formations in my country, Serbia. It was relatively easy for me to look for possible folklore related to such places. I found a few of these, but to my greatest disappointment, archaeologists showed no interest, nor did they share my enthusiasm. None of the circular formations in Serbia has been archaeologically investigated so far. Nothing has changed since 2009.

I remember that I discovered the first two circular Yogini temples by accident, while looking for information on ancient Greek circular temples (tholos). I was immediately fascinated. Yogini statues from Bhedaghat were particularly impressive. I seemed to feel the power of the Sri Phanen-dri's gaze even here in Belgrade. My first readings of Puranic literature revealed the existence of a substantial body of myths about those mysterious beings called Yoginis. Everything was there: the circular temples, their mistresses (Yoginīs) and myths about them, together with beliefs and rituals... Even though I was aware that a huge task was in front of me, it seemed like a feast. But, I wasn't sure that I was invited to it because the difficulties were enormous. I have never seriously studied the culture of India (although I have read several Indian scriptures, such as The Rgveda, The Mahabharata and The Ramayana), have never studied Sanskrit and have never practiced Yoga. But, more than anything else, I love books and I can read English, which has made a significant part of traditional Indian religious literature available. I had a place to start without any specific intention to write a book.

The first results began to appear around 2015. I was writing down my findings so I wouldn't forget them. At one point all those records slowly started to look like a book. I read the text again and was not satisfied: it was too extensive (about 500 A4 pages). I said to myself: If I can't communicate my results in 200 pages, then I'm not sure I've fully understood what I'm supposed to be talking about. That's why I stopped writing and directed my energy towards acquiring more knowledge on Astronomy and Geodesy, in order to prepare myself for further work. Such a state lasted until 2020, when I managed to acquire several new translations of Tantric literature, such as Yoginihrdaya, Vamakeivara Tantra and Kaulajnananirnaya, All three, and especially the first two, offered a multitude of astronomical concepts, incorporated into the religious teachings of Tantra.

Kaulajnananirnaya, the ancient scripture of Tantra (Ch. 1. v.1) begins like this:

O Devi, eighteen types of knowledge exist in the proximity of Kula. (1)

This is only one verse, but it already offers three concepts that should be explained.

Tantra, as a corpus of teachings and rituals, occurred relatively early in Indian society, about the fifth century CE. It flourished during the 9.13th century and is still active in present times. Although never fully incorporated into orthodox Hindu teachings, it has indisputably exerted a strong influence on both Hinduism and Buddhism. Religious scriptures of Tantra are written in Sanskrit, but its priests still have a low status within the Brahmin caste.

Kula is the Sanskrit word for a clan. Kula "Clan"/ practices designate the oldest name for Tantra. First practitioners seem to be the variety of Saiva ascetic groups, existing over the first few centuries CE. In addition to the Pasupatas, ("masters of wild beasts") and Lakulīšas ("with a club"), we hear of Kalamukhas, Bhairavas, Aghoris ("non-terrifying"), Käpälikas (the naked ascetics, smeared with ashes, with bawls made of human skulls). They were the renunciates who placed themselves outside society and were believed to possess magical powers. These renunciates or outsiders were viewed ambivalently or negatively by the surrounding 'respectable' society, while at the same time valued or even viewed as necessary for their ritual services. Kula was one of the earliest traditions inside that corpus of teachings and rituals in Tantra. Perhaps it would be more correct to designate this practice by the term Proto-tantra.

A striking innovation in the course of the eighth to tenth centuries was a new series of yogic practices and techniques based on a 'subtle anatomy of the practitioner's body. Specifically, these practices assume an internal subtle physiology of the body (or rather of the body-mind complex) made up of channels (nadhi), through which substances of some kind flow, and points of intersection (cakra) at which these channels come together A key element of the "subtle body practices is their close connection with sexual practices. Sexuality (eros) was recognized as a powerful source of energy. Yoga, as the technique of mental and physical cultivation, was widely accepted in Tantra. The main goal for a practitioner was to achieve the altered state of consciousness with the direct religious experience - the unity with the deity. Kula practices evolved and were adopted by the wider community of merited householders including part of the ruling elite. This stage in the evolution of Tantra was named Kaula (Time) tradition.

Traditionally, Tantra is described as a set of teachings and rituals. Educated individuals with a more detailed insight into the meaning of Tantra would explain that the followers, as opposed to orthodox Hindu teachings, do not consider the external reality to be an illusion. They believe that what is considered "unclean" or "sin" does not come from the external reality, but has its roots in the internal, spiritual reality. Therefore, their goal is not to deny the external reality, but to overcome it. According to this teaching, a person who has achieved spiritual purity (by practicing both yoga and meditation) can defile anything coming from outside. In their ritualistic practice they use to consume "forbidden" or "impure" things, such as wine (madya), fish (matsya), meat (mamsa), roasted cereal seeds (mudra), including ritual sex (mithuna). Sanskrit words marking all of these concepts begin with the letter "m", so called "5 M" (Kulārnava Tantra, Ch. 5).

Tantra is widely studied in present time. It is precisely the spiritual aspect that has been the main subject of attention. Researchers, as well as people outside of science, are interested in spiritual development and are looking for a way to achieve it.

Even at first glance it is obvious that Tantra has a developed cosmology and that some astronomical knowledge was built into its foundations. That is exactly what this book is looking for- the astronomical knowledge in early medieval Tantra. It seems to be a neglected topic, worth researching. Astronomy is considered to be the oldest science and it is worth the effort to look for it in a certain culture.