The five fundamental theoretical texts of Indian astrology were composed during the Vedic period and the post-Vedic period. The Surya Siddhanta, Romaka Siddhanta, Paulisa Siddhanta, Vasishtha Siddhanta, and Pitamaha Siddhanta are the five fundamental theoretical texts of Indian astrology. These five fundamental texts of Indian Vedic astrology contain detailed descriptions of many celestial phenomena. Many scholars and masters of astrology emerged in India later on. They composed numerous texts on astrology. Among these many astrologers, Aryabhata, Bhaskaracharya, Acharya Varahamihira, Rishi Kashyapa, and Rishi Bhrigu are some of the prominent astrologers who lived in India. While observing celestial events, these astrologers began to develop various ideas about space and the universe and formulated their theories. These ancient Indian astrologers began to describe the ideas arising from their astronomical observations in various symbolic forms.

In their texts, these ancient Indian astrologers discussed the following topics in detail:

1) Does the sun revolve around the earth, or does the earth revolve around the sun?

2) Is the earth spherical or not?

3) Why do the planets and stars in the sky appear to move in circular orbits?

4) Why does the moon appear to change its shape?

5) Why does the sun appear to move towards the north and sometimes towards the south?

6) Why don't the planets and stars in space fall to the earth?

7) Is the sun that rises in the east every day a new sun or the same sun as yesterday?

8) Objects thrown into the air fall back to the earth, but why don't birds fall to the earth from the air?

9) Is there only one universe in the world, or are there many universes?

These ancient astrologers began to express their opinions on many such questions in their texts. Among these astrologers, Acharya Varahamihira was a prominent astrologer who lived in the fifth century AD, as mentioned in many texts. Acharya Varahamihira composed major works on astrology such as Panchasiddhantika, Brihajjataka, Brihat Samhita, Brihat Vivahapatala, Brihat Yatra, and Yogayatra. In these texts, Acharya Varahamihira has presented his views on various topics of astrology. In the Panchasiddhantika, Acharya Varahamihira has written a chapter called Trailokya Sansthan. In this chapter, Acharya Varahamihira has expressed his views on what Trailokya (the three worlds) is and other related topics. Even in today's modern times, the concept of Trailokya or the three worlds is prevalent in India. So, let's now see what Acharya Varahamihira has written in the chapter Trailokya Sansthan in the Panchasiddhantika and what opinions he has expressed on these subjects.

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Panchasiddhantika (Thirteenth Chapter:)

Bhuva: Sansthanam (The position of the Earth in space)

1) Meaning: The spherical Earth, made of the five elements, is situated in space within a cage-like structure filled with infinite stars.

2) Meaning: On this entire Earth, various types of trees, mountains, seas, cities, rivers, etc., are situated. Mount Meru, which is the North Pole of the Earth, is the abode of the gods. Exactly opposite to it, at the South Pole, is the abode of the Asuras or demons.

3) Meaning: Just as the reflection of an object in water appears inverted, similarly, the Asuras appear inverted to the gods, and the gods appear inverted to the Asuras. Since the South Pole of the Earth is exactly opposite to the North Pole, it appears like a reflection of the North Pole in water. 4)

4) Meaning: Just as we see flames rising upwards and an object thrown upwards falling back down, the gods experience the same on Mount Meru, which is the North Pole, and the demons or Asuras experience it at the South Pole.

Bhūbhramaṇam (Regarding the Earth's Rotation)

5) Meaning: The Earth's axis extends upwards and downwards in space. The celestial bodies bound to this axis of the Earth revolve in a circular motion around the Earth's axis due to the influence of a wind called Pravaha.

6) Meaning: Some people say that just as a clay pot revolves on a potter's wheel, the Earth revolves around its axis, and the stars in space are stationary. If this were true, it would be impossible for an eagle flying in the sky to return to its nest.

7) Meaning: If it is assumed that the Earth is rotating around its axis from west to east at a very high speed, then we would see erected flags fluttering towards the west, just as if a man were running eastwards with a flag in his hand, the flag would be seen fluttering towards the west. But we do not see this happening. Some say that the Earth's rotational speed is very slow, but if this rotational speed is very slow, how can the Earth complete one revolution around its axis in a single day?

8) Meaning: The Jain Arhantas have written that there are two suns and two moons in this world, which rise one after the other. If this is considered true, then why does the line connecting the sun and the celestial pole appear to rotate only once a day in space?

Devāsurāṇā Sthiti (The Position of Gods and Demons)

9) Meaning: The gods at the North Pole see the sun in the Aries constellation rotating on the horizon in a clockwise direction. People at the equator see the sun in the constellation Aries passing directly overhead. The demons at the South Pole see the sun in the constellation Aries moving along the horizon in a counter-clockwise direction.

10) Meaning: The gods at the North Pole see the sun in the constellation Gemini moving across the sky at an altitude of 24°, while at the same time, people in Ujjain see it directly overhead. This is because the Earth's axis is tilted by approximately 24 degrees.

11) Meaning: Therefore, when the sun is at its zenith, a person standing in Ujjain casts no shadow, while a person north of Ujjain casts a shadow tilted towards the north, and a person south of Ujjain casts a shadow tilted towards the south.

12) Meaning: Some people say that when the sun is in the constellations Aries, Taurus, and Gemini, it is daytime for the gods at the North Pole, and when the sun is in the constellations Cancer, Leo, and Virgo, it is nighttime for the gods at the North Pole. How can this be correct?

13) Meaning: How is it possible that when the sun is at the same northern declination, the gods at the North Pole see it in the three constellations Aries, Taurus, and Gemini, but not in the three constellations Cancer, Leo, and Virgo?

Here, Acharya Varahamihira's point is that when the sun is in the six constellations Aries, Taurus, Gemini, Cancer, Leo, and Virgo, during the Uttarayana (northern solstice), it should be continuously visible to the gods at the North Pole, meaning it should be daytime for the deities at the North Pole.

Zodiacal Division and Measurement

14) Meaning: For the gods at the North Pole, the celestial North Pole is directly overhead. Any semicircle passing overhead represents a line of latitude on Earth. The distance from the celestial North Pole overhead to the horizon is three zodiacal signs, or 90 degrees. Dividing these 90 degrees by 90 leaves one degree.

15) Meaning: These divisions of the overhead celestial sphere in degrees are parallel to the degrees on the Earth's surface. The distance between two degrees on Earth is approximately eight and eight-ninths yojanas.

16) Meaning: That is, 90 degrees is considered to be equal to 800 yojanas. When a man standing on Earth sees the sunrise in the east, the sun is directly overhead for a man standing at 90 degrees to the east.

Lanka Ujjain Location

17) Meaning: Since Ujjain and Lanka are on the same latitude, when the sun is at its zenith in Lanka, it is also at its zenith in Ujjain. The duration of the day is different in Ujjain and Lanka; only when the sun is on the equator is the duration of the day the same in Ujjain and Lanka.

Earth's Measurement (Earth's Circumference)

18) Meaning: The circumference of the Earth is 3200 yojanas. When the sun is on the equator, it is visible at all degrees from the North Pole to the South Pole, and the duration of day and night is equal.

19) Meaning: The location of the North Pole is 586 ⅔ yojanas north of Ujjain. The location of the North Pole is 800 yojanas north of Lanka.

Visibility of the Sun

20) Meaning: At any longitude, the sun is inclined towards the south by the same number of degrees as the North Pole is inclined towards the north of the horizon.

21) Meaning: At a distance of 373 ⅓ yojanas north of Ujjain, the celestial sphere is not continuous, meaning there is a break in the celestial sphere or the universe.

22) Meaning: At the longitude located 373 ⅓ yojanas north of Ujjain, the sun can be visible for the entire day (24 hours). As you travel north from this longitude, the sun may be visible for more than one day, and this duration of daylight progressively increases. At the North Pole, the sun is visible continuously for six months, meaning there is six months of day and six months of night at the North Pole.

23) Meaning: North of Ujjain, at a distance of 403 5/9 yojanas, the constellations of Sagittarius and Capricorn are never visible.

24) Meaning: North of Ujjain, at a distance of 482 yojanas, the constellations of Scorpio, Sagittarius, Capricorn, and Aquarius are never visible.

25) Meaning: North of Ujjain, at a distance of 586 2/3 yojanas, at the North Pole, the southern hemisphere of space is not visible, and the constellations of Libra, Scorpio, Capricorn, Sagittarius, Aquarius, and Pisces are never visible.

26) Meaning: For people on the equator, the North Star is always visible on the horizon, while for people on Mount Meru, i.e., the North Pole, the North Star is always visible directly overhead in the sky. Also, in the region from the equator to the North Pole, the North Star is visible at an angle from 0° to 90°.

27) Meaning: For the gods residing on Mount Meru, i.e., the North Pole, the sun is continuously visible for six months, that is, when the sun is in the constellations of Aries, Taurus, Gemini, Cancer, Leo, and Virgo. When the sun moves into the next six constellations, namely Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces, it is continuously visible for six months to the demons at the South Pole.

28) Meaning: For them, the Aries constellation is always the ascendant sign, and Mars is always the lord of the ninth and twelfth houses of the ascendant. 29)

Meaning: Lanka is located directly below the celestial equator, and the equator itself serves as the prime meridian for Lanka. The celestial sphere is divided into two equal parts at Lanka; the North Pole is at the center of the northern part, and the South Pole is at the center of the southern part.  Also, day and night are of equal duration, 30 'nadis' each. Every place on the Earth's equator could be called Lanka, but here, Lanka refers to the point where a straight line drawn from Ujjain towards the South Pole intersects the equator.

30-32) Meaning: Place a plank with a flat surface in an elevated position. Keep its surface level with the horizon and eye level, and its sides parallel to the north-south and east-west directions. Suspend a sighting tube from the middle of the southern edge, equal in length to the north-south length of the plank. Look through one end of the sighting tube and adjust the lower end of the instrument so that the North Star is visible through the tube. When fully lowered, it will point towards Lanka; when fully vertical, it will point towards Meru. In this way, we can measure the local latitude at that place.

33) Meaning: The perpendicular point falling on the plank from the location's edge while observing the North Star is R Sin of that location's latitude. The base formed at that location is R Cosine of that latitude. This R cosine line aligns with the north-south direction.

34) Meaning: Learned people determine the location of the North Pole and the measurement of the Earth through careful observation, just as scholars measure the salinity of a small amount of water to determine the salinity of all the water.

Lunar Phases

35) Meaning: Just as an earthen pot placed in the sun is illuminated on one side by the sun and the other part is kept in darkness by its own shadow, similarly, one part of the moon is illuminated by the sun, and the other part is kept in darkness by the moon's own shadow.

36) Meaning: Just as the sun's rays reflect from a mirror placed in a house and illuminate the house, similarly, the sun's rays reflect from the moon and illuminate the Earth.

37) Meaning: The part of the moon illuminated by sunlight increases every day. This illuminated part increases as the moon moves westward. 38)

Meaning: The Sun is visible to the ancestors residing anywhere on the Moon for half of a fortnight because the visible part of the sky there extends only up to 90 degrees overhead.

39) Meaning: Further above the Moon are the orbits of Mercury, Venus, the Sun, Mars, Jupiter, and Saturn, and beyond them are the fixed stars. All these planets revolve in their respective orbits at a uniform speed.

40) Meaning: Just as the spokes of a wooden oil press are thicker near the central wooden shaft and the distance between the spokes increases further away, similarly, the distance between the constellations increases in space.

41) Meaning: Because the Moon is situated closest to the Earth in space, it travels at the fastest speed in the celestial sphere, while Saturn, being the farthest, travels at the slowest speed.

42) Meaning: The lords of the twelve months of the year are arranged starting from the closest planet, the Moon, to the farthest planets. The lords of each hora (hour) start from Saturn and proceed to the closest planets. The fifth planet in increasing order is the lord of the day, while the sixth planet in increasing order is the lord of the year.

From the above chapters titled 'Trailokya Sansthan' from Acharya Varahamihira's book Pancha Siddhantika, we understand how meticulously these astrologers of that time observed the size of the Earth, its extent, its speed, its orbit, the speed of the Sun, the speed of the Moon in the sky, and the speeds of other planets and stars. Also, the information given in this chapter about the position of gods and demons or Asuras on Earth, and about Mount Meru, shows how much knowledge these astrologers possessed regarding these subjects as well.