How does Vedic cosmology explain the passage of the seasons?
Śrīmad-Bhāgavatam explains the earth is a globe, just as studied in modern cosmology; the main difference is that the movements of the sun and stars are studied from a geocentric perspective.
The description of the Vedic universe in the 5th canto of Śrīmad-Bhāgavatam is not easy to understand. When we go through the text, without deeply studying it, many misunderstandings can appear.
The first is that the earth is flat. That is the opposite of what the model indicates. Prabhupada explains that Bhū-mandala is formed by different planets and that the sun and all stars travel daily around Dhruvaloka, and this conclusion is essential to understanding the model described in the Śrīmad-Bhāgavatam.
In the model described in the Śrīmad-Bhāgavatam, the earth is a globe, just as studied in modern cosmology; the main difference is that it is not tilted, and that the movements of the sun and stars are explained from a geocentric perspective. This was already discussed in other articles, so let’s move on.
The days and nights are explained in the Vedic model by the daily orbit of the sun and stars around Druvaloka, the Polestar. It may appear strange to imagine that the whole sky rotates, but that’s what we see when we look at the sky. From our perspective, the whole sky rotates every 24 hours:
We then have the annual movement of the sun, which explains the passage of the seasons.
The Bhāgavatam describes that the sun sometimes passes through the north, south, or through the equator. This refers to the sūrya-mārga, or the ecliptic circle, which is not identical with the celestial equator. The sun stays part of the year above the equator, part under it, and with the two lines crossing at two points of the year. You can see how this works in this diagram:
The central horizontal line is the equator, which divides our planet into two exact halves. In the model of the Bhāgavatam, this is also the equator of Bhū-mandala.
The upper horizontal line is the Tropic of Cancer, which marks the upper limit of the path of the sun, while the lower horizontal line is the Tropic of Capricorn, which marks the lower limit of its path.
Imagine someone standing exactly at the line of the equator, facing east. In this position, the line of the equator appears as the middle of the sky. However, the sun will rarely pass directly overhead. Half of the year, the sun will pass to the left of the sky (north, in the direction of the Tropic of Cancer), and the other half to the right (south, on the side of the Tropic of Capricorn). Only two days per year, the sun will pass directly overhead. This north–south shifting of the passage of the sun is caused by the sun’s annual motion along the ecliptic, the path of the sun shown in the picture. That’s what Śukadeva Goswami describes in the Śrīmad-Bhāgavatam as the sun traveling through the constellations (rāśis), sometimes to the north and sometimes to the south.
Sukadeva Gosvami explains:
“When the sun passes through Meṣa [Aries] and Tulā [Libra], the durations of day and night are equal. When it passes through the five signs headed by Vṛṣabha [Taurus], the duration of the days increases [until Cancer], and then it gradually decreases by half an hour each month, until day and night again become equal [in Libra].
When the sun passes through the five signs beginning with Vṛścika [Scorpio], the duration of the days decreases [until Capricorn], and then gradually it increases month after month, until day and night become equal [in Aries].
Until the sun travels to the south the days grow longer, and until it travels to the north the nights grow longer.” (SB 5.21.4-6)
The movement of the sun around the zodiac (passing north or south of the celestial equator) results in the days becoming longer or shorter, as the seasons go by. The sun goes through the twelve signs during the year.
This explanation becomes easier to follow when we look at the wheel of the zodiac.
The text says, “When the sun passes through Meṣa [Aries] and Tulā [Libra], the durations of day and night are equal.”
These are the two equinoxes (vaiṣuvata), when the sun is aligned with the equatorial plane and the duration of the days and nights is approximately equal at most latitudes. This happens only twice per year, when the sun enters Meṣa (Aries) and Tulā (Libra). In the modern calendar, this corresponds approximately to March 20 and September 22:
In the model described in these verses, the equator of our planet also corresponds to the celestial equator of Bhū-maṇḍala, since in the Vedic model, the earth is not tilted. The same phenomenon should thus be observed in the other planets that compose the planetary system of Bhū-mandala.
Let’s take Aries as the starting point. When the sun enters Aries (nine o’clock on the wheel of the zodiac of the illustration), the day and nights are approximately the same. From Aries, the sun goes to Taurus (Vṛṣabha) and then Gemini (Mithuna) and Cancer (Karkaṭa). Here, the sun is moving northward of the equator (udagayana). The practical effect will be opposite in the two hemispheres and will vary according to the latitude. The Bhāgavatam explains it from the point of view of someone in central India. At these latitudes, the transition makes the days longer at a rate of approximately half an hour for each sign, with the sun’s daily arc becoming progressively longer.
When the sun enters Cancer, the days become very long in relation to the nights: approximately 13.5 hours for the days and 10.5 hours for the nights. This is the summer solstice.
After Cancer, there is a reversal. With the sun entering Leo, the days become shorter by about half an hour, and then half an hour more in Virgo. By the time the sun enters Libra, the days and nights are again approximately equal.
We then have the second half of the year, when the sun goes to the southern hemisphere (dakṣiṇa-ayana) and the days become shorter, leading to the colder season. As the sun enters Scorpio and then Sagittarius, the days become progressively shorter, reaching their minimum duration in Capricorn. That’s the winter solstice.
From there, there is again a reversal, with the days gradually increasing as the sun goes through Aquarius and Pisces, until they once more become equal back in Aries. This is also indicated in the text: “When the sun passes through the five signs beginning with Vṛścika [Scorpio], the duration of the days decreases [until Capricorn], and then gradually it increases month after month, until day and night become equal [in Aries].”
In short, the northward movement results in longer days and the southward movement in shorter days. This is a concise explanation of how the movement of the sun results in seasonal change.
Śukadeva Goswami also mentions that “While passing toward the north, toward the south or through the equator, in accordance with the order of the Supreme Personality of Godhead, it is said to move slowly, swiftly or moderately.”
What does it mean?
This change in the apparent speed of the sun and the movement through the signs of the zodiac is easier to understand when we see the annual path of the sun in the sky. If we take a photo of the sky every day at the same time, and combine the photos into a single image, we will see a movement similar to this. In modern cosmology, this is called analemma:
You can notice the movement of the sun through the signs of the zodiac and that the apparent speed of the sun changes during the annual path, with the sun appearing to move slowly on the two extremes, and faster in between.
During the uttarāyaṇa period (beginning with the winter solstice), the length of the days increases slowly as the sun moves through Capricorn, Aquarius, etc., from the minimum of the winter solstice. On the other half of the movement, starting from the summer solstice, as the sun moves through Cancer, Leo, etc., the length of the days shortens quickly. During the equinox periods, as the sun moves through Aries and Libra, the change happens at a moderate speed.
In this way, the Śrīmad-Bhāgavatam describes the practical phenomenon that is observable from our planet. The same is also studied in modern astronomy; it is just explained differently. Modern models explain it through the elliptical orbit of the earth around the sun, and the tilt of the earth’s axis, while the Bhāgavatam explains it in terms of the two movements of the sun, moving through the zodiac and around Dhruvaloka.
The movement of the sun is supposed to be similarly observable from the other planets that compose Bhū-mandala. In other words, the sun rises in the east and sets in the west and goes through the signs of the zodiac, producing the seasons; the days have 24 hours, and so on. In this way, all human beings in these different planets experience the passage of time in the same way. The demigods living on top of Mount Sumeru, on the other hand, see the sun as always moving overhead (similar to what we observe in the North Pole). Their days and nights are produced solely by the annual movement of the sun, north and south of the plane of Bhū-mandala, which takes a whole year. In other words, 24 hours for them are 360 days for us.
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