Weekdays (“Sunday”, “Monday”, etc.) are not part of a Vedic calendar, but Sūrya Siddhānta describes how they come about. Here are the details…

Essential Human-Scale Vedic Time Units

Sūrya Siddhānta defines a year as the time it takes the Sun to pass to a tropical waypoint (a particular solstice or equinox).

It divides a year into 12 units, “months” – each one the amount of time it takes the Moon to cycle through all its phases.

It divides each month into 30 units, “days” – each one the amount of time it takes the Sun to pass a terrestrial waypoint (typically, the eastern horizon).

It divides each day into 60 units, “beats” (nāḍi) a.k.a. “moments” (muhūrta). Each of these is further divided into 60 sub-units, “semi-beats” (vināḍi). Finally, each of these is divided into 6 tiny units, “breaths” (prāṇā).

How this Relates to the Zodiac

You may have noticed that the zodiac is a spatial reflection of this temporal blueprint.

• Semi-beats are identical to zodiac-seconds.
• 60 semi-beats in a beat = 60 zodiac-seconds in a zodiac-minute.
• 60 beats in a day = 60 zodiac-minutes in a zodiac-degree.
• 30 days in a month = 30 degrees in a zodiac-sign.
• 12 months in a year = 12 signs in the zodiac.

How this Relates to our Modern Calendar Units

You may have noticed that the Vedic Time Units don’t mention some things we are very familiar with:

• Weekdays
• Hours
• Minutes
• Seconds

Although these units aren’t fundamental, they can be derived from the fundamentals, and are therefore “secondary” time units. In this article I will explain the origin of weekdays found in Sūrya Siddhānta.

Vedic Weekdays

Sūrya Siddhānta 1.50-52 describes how to find the planet that is predominant (the “lord”) on any given day, month, or year. This will set up pattern of 7 years, 7 months, and 7 days, which will recognize as the day pattern of our familiar “week.”

The method, in summary, is this:

• The first day of any yuga is always ruled by the Sun (“Sunday”)
• The next 6 days are ruled by planets in their “order.” (Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn)
• Calculate the number of days elapsed sine the beginning of the yuga.
• Divide that by 7
• The remainder is the weekday

Was 51 and 52 added to Chapter 1 later?

It is easy to make an argument that it was. Here is why:

• The 7-cycles for year, month and day isn’t used anywhere else in Sūrya Siddhānta, and the concept is only even mentioned in one other place (12.78-79). And even that is nothing but a paraphrase of 1.51-52.
• Since it isn’t an important system, it seems unlikely it would come, as it does, before an extremely important system – using the sum of days elapsed from the beginning of a yuga to locate the positions of planets.
• It relies on an order of planets which it doesn’t define.
• The mechanics to create the of the weekdays relies on days being divided into 24 hours – but Sūrya Siddhānta doesn’t talk about dividing a day into 24 parts.

In short, since it is not remotely integral with the rest of the techniques or concepts in the book, and since it cannot be used without other techniques or definitions not given in the book, it does in fact seem that these texts were added to Sūrya Siddhānta later on.

But, agreeing on this is not necessary. We can still reconcile the 7-day week with the Vedic calendar

Reconciliation

Weekdays are not part of a Vedic calendar, but lordship over days, months, and years may have been. So we can keep separate cycles of 7 years, 7 months, and 7 days alongside the units of the actual Vedic calendar.

At some point in history the cycle of 7 days became an important part of our calendars. Probably this first happened outside of India and gradually influenced Indian’s to downplay their tithi (“lunar phase”) based 15-day units in favor of this 7-day unit.