Gregorian

March 21, 2023

©bigstockphoto.com/dubassy

The March equinox occurred yesterday, March 20, at 5:24 pm EDT.  This marks the astronomical beginning of the spring season in the Northern Hemisphere and the autumn season in the Southern Hemisphere.  While I have always thought of this happening on March 21, the date of the equinox shifts every year.  In the Northern Hemisphere the spring equinox, or March equinox or vernal equinox, occurs when the Sun crosses the celestial equator going south to north.  It is called the “celestial” equator because it’s an imaginary line in the sky above the Earth’s equator.  On the March equinox, the Northern Hemisphere and Southern Hemisphere receive roughly equal amounts of sunlight as neither hemisphere is tilted more toward or away from the Sun than the other.  Spring arrived on the 21st of March during most of the 20th century, but the event slides earlier and earlier during the 400-year Gregorian calendar cycle, and the final March 21st equinox for this Gregorian cycle was in 2007.

When I looked online, I found when Julius Caesar established the Julian calendar in 45 BCE, he set March 25th as the date of the spring equinox as this was already the starting day of the year in the Persian and Indian calendars.  The Julian year is longer than the tropical year by about 11.3 minutes on average (1 day in 128 years), which caused the two equinoxes to “drift” on the calendar.  This drift induced Pope Gregory XIII to establish the modern Gregorian calendar in 1582 CE.  Gregory wanted to continue to conform with the edicts of the Council of Nicaea in 325 CE concerning the date of Easter, and wanted to move the vernal equinox to the date on which it fell at that time and maintain it at around that date in the future.  This was achieved by reducing the number of leap years from 100 to 97 every 400 years.  There was still a small residual variation in the date and time of the vernal equinox of about ±27 hours from its mean position.  While the variation is less, the equinox date still has some drift in the Gregorian calendar.

Today the Gregorian calendar is the internationally accepted civil calendar and is also known as the Western or Christian calendar.  It is a solar calendar based on a 365-day common year divided into 12 months of irregular lengths.  Eleven of the months have either 30 or 31 days, while the second month, February, has only 28 days during the common year.  However, (nearly) every four years is a leap year when one extra (intercalary) day, is added on February 29th, making the leap year in the Gregorian calendar 366 days long.  The days of the year in the Gregorian calendar are divided into 7-day weeks, and the weeks are numbered 1 to 52 or 53.  The international standard is to start the week on Monday, but several countries, including the US and Canada, count Sunday as the first day of the week.  The Gregorian calendar was first adopted in Italy, Poland, Portugal, and Spain in 1582 and included the new formula for calculating leap years.  Leap years occur when the year is evenly divisible by 4, unless it can be evenly divided by 100, then it is not a leap year.  But, if the year is also evenly divisible by 400, it is a still a leap year.  Who says time is not relative?

THOUGHTS:  Equatorial countries abide by the Gregorian Calendar based on differences in sunrise and sunset even though these do not make sense.  My sister was traveling in Bali located close to the equator and mentioned the sun comes up and goes down around 6 am/pm every day of the year.  The Western or Gregorian calendar is international despite other existing systems.  This reflects the dominance exerted by western Europe during the Age of Discovery, even while many did not think they needed to be discovered.  The globalization of our world over the last decades has made a single reference point (calendar) convenient, but we need to remember the calendar used reflects Western culture and thought.  Act for all.  Change is coming and it starts with you.