Friday September 23, 1566
A date scroll with Latin text from โ€œThe Extremes of Good and Evilโ€ by Cicero, written in 45 BC.

September 23, 1566: Day of the Week

September 23, 1566 was the 266th day of the year 1566 in the Gregorian calendar. There were 99 days remaining until the end of the year. The day of the week was Friday.

The day of the week for September 23, 1566 under the old Julian calendar was Monday. Did you notice the difference with the Gregorian calendar?

If you are trying to learn Spanish then this day of the week in Spanish is viernes.

A person born on this day will be 458 years old today. If that same person saved a Nickel every day starting at age 7, then by now that person has accumulated $8,242.15 today.

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Here’s the September 1566 Gregorian calendar. You can also browse the full year monthly 1566 calendar.

September 1566
SunMonTueWedThuFriSat
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Zodiac & Birthstone

Virgo is the zodiac sign of a person born on this day. Sapphire is the modern birthstone for this month. Agate is the mystical birthstone from Tibetan origin that dates back over a thousand years.

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September 23, 1566 by the Numbers

  • 167,400 days since September 23, 1566
  • 458 years, 3 months, and 27 days ago
  • 5,499 months since then
  • September 23 is in the 38th week of the year 1566 (ISO 8601)
  • 23,914 weeks ago
  • The year 1566 is not a leap year

Gregorian versus the old Julian calendar

A note to students, teachers, scholars and anyone else passionate about this topic. As stated in the front page, this website is using the Gregorian calendar as the basis for all “day of the week” computation whether or not the Gregorian calendar is relevant for the date in question (September 23, 1566). Educators should point out the primary reason why Pope Gregory XIII introduced a new calendar system in October 1582. That is, to make the computation for the annual date of Easter more accurate since it is the foundation of the Christian faith.

Even with that purpose in mind, the Gregorian calendar too will become out of sync. It has a known approximation error of about one day for every 7,700 years assuming a constant time interval between vernal equinoxes (which is not true). This is better compared to the one day for every 128 years error of the Julian calendar.

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