A Matter of Time

Celebration of Inquiry 2004

Louis Keiner, Dan Ennis

Coastal Carolina University

How long is a year?

Or first: what is a year?

How do we measure a solar year?

Year Animation

We find that the year is about 365.25 days long.

(If the Shockwave animation does not play automatically,right click on the box and select ‘Play’)

What happens if your calendar year is not the right length?

If your calendar year is shorter than a solar year…

If your calendar year is longer than a solar year…

Months

• Lunar Month = 29.5306 days– (new moon to new moon)

• 12 lunar months 354.3672 days. – << 365 days!

What’s an astronomer/astrologer/priest to do?

• Greek – lunar, add 90 days each 8 years.• Jewish – lunar, add a month each 3 years.• Islamic – lunar, no corrections.• Chinese – lunar, add 7 months during 19 years.

Of course the Romans……

Roman Calendar I - c. 735 B.C.E

10 Months – 304 days 1. Martius

2. Aprilus

3. Maius

4. Junius

5. Quintilis

6. Sextilis

7. September

8. October

9. November

10. December

Roman Calendar II - c. 700 B.C.E

12 Months – 354 days 1. Januarius2. Februarius3. Martius4. Aprilus5. Maius6. Junius7. Quintilis8. Sextilis9. September10. October11. November12. December

Add a month as needed to keep the seasons correct.

Julius Caesar

Or rather, “Julius,” as in Caesar. In 45 B.C. (or at least what we call 45 B.C. using our calendar), Julius Caesar replaced the chaotic Roman calendar with a system based on a year of 365.25 days—close to the actual length. The .25 days was dealt with by having a “leap” year every four years.

Roman Calendar III - c. 46 B.C.E

12 Months – 365 days 1. Januarius 312. Februarius 303. Martius 314. Aprilus 305. Maius 31 6. Junius 307. July 318. Sextilis 309. September 3010. October 3111. November 3012. December 31

Add a day every four years to keep the seasons correct.

365.242190

(Well, not exactly…a Tropical Year was exactly 365.242190 days long in the late 1990s. To get the

exact number for 2004, or 1804, or 2204, we need…)

The year is exactly

days long

days, where

10 2 10 3365.2421896698 0.00000615359T 7.29x10 T 2.64x10 T ...

JD=Julian Date

JD 2451545T

36525

The Julian Calendar “loses” one day every 128 years.

A Little Math and a Pope

By the sixteenth-century, Europe--using the Julian calendar--was in something of a crisis.

First, the Julian calendar had been “losing” days for centuries.

Second, the Christians liked dating things from the birth of Christ (the Romans of Caesar’s time, for obvious reasons, did not).

Third, the date of Easter, for reasons to complicated to relate, was calculated using a combination of the lunar cycle and the vernal equinox. Every year Easter got a little further from the first day of spring.

Pope Gregory XIII decided enough was enough.

The Gregorian Calendar

1. Nine days--October 5-14, 1582--were struck from the calendar. This would allow Europe to “catch up.”

2. The Julian leap year rule was changed. Leap years on all century years not divisible by 400 were eliminated.

3. The Gregorian calendar--accurate to one day every 3300 years—seemed to be the solution.

So why was it unpopular?

TRANSITION SLIDE

The “Georgian” Calendar was understood to be the “Roman Catholic” calendar…it was adopted rather quickly by predominantly Roman Catholic countries…..

Italy—1582

France—1582

Spain—1582

Portugal—1582

Bohemia—1584

Moravia—1584

Poland—1586

Hungary—1587

Countries with a mixture of Catholics and Protestants split—the more Catholic areas went with Gregory, but places where Protestants held authority stuck with the Julian system. Thus in the late 1500s both Switzerland and Germany had two calendars. It goes without saying that Gregory’s calendar was not a hit in areas that were Greek Orthodox …or Muslim.

Which Brings Us To England…

What Day is it in Great Britain?

By the mid-eighteenth century the Julian (English) calendar was eleven days behind the Georgian Calendar (which by now most of Europe had adopted).

July 1, 1750 in England was the same day as July 12, 1750 on the continent.

Wait—there’s more…

HAPPY NEW YEAR?

The Gregorian calendar marks the New Year (as we know) on January 1st. The Julian calendar marks the new year on March 25. So for about three months each year

England and the continent were on different years: Thus January 1, 1750 in Great Britain=January 12, 1751 on the continent.

English Trade was suffering…

How can you

enforce a contract

schedule a trading voyage

calculate interest

When you disagree on the date?

Lord Chesterfield and The Calendar Act

1. March 24, 1751 was by custom New Year’s Eve, so that made March 25, 1752, New Year’s Day in Great Britain. This was the last March New Year in British history.

2. Then 1752 was allowed to proceed normally until September. September 1, 1752 was followed not by September 2, but instead by September 14, 1752.

3. The year 1752 ended not on March 24, as had been the English practice, but on December 31. Thus January 1 marked the first day of 1753.

4. Then Britain simply followed standard Georgian practice.

Oddly enough, that meant the year 1752 was only 293 days long.

Finally, in 1751 (Julian and Georgian!) Parliament acted. The actions proscribed by the calendar act were complicated:

The Riots

The Calendar Act provoked a storm of protest. There were supposedly riots in Oxfordshire, London and Greenwich. The Georgian calendar was associated with Roman Catholicism. Some protested the Government’s “stealing” of days. Laborers noted that they were paid daily wages but had to pay monthly rents.

A contemporary ballad put it this way:

In seventeen hundred and fifty-three

The style was changed to Popery,

But that it is lik'd, we don't all agree;

Which nobody can deny.

When the country folk first heard of this act,

That old father style was condemned to be rack'd,

And robb'd of his time, which appears to be fact,

Which nobody can deny…

William Hogarth produced an engraving in 1754 in which a mob outside a window waved a banner saying “Give Us Back Our Eleven Days!”

Britain’s American Colonies had to adopt the change as well, but the new calendar was welcomed by many colonial merchants as a means to simplify trade.

Ben Franklin, who supported the change, took a more philosophical point of view, saying:

“It is pleasant for an old man to be able to go to bed on September 2, and not have to get up until September 14.”

The Calendar Act solved the problem for the moment, but there are still issues to be resolved. For example, the actual year is not 365.25 days long—if so, the Georgian calendar would be perfectly accurate. It is instead closer to 365.242190 days long. So even as we speak our calendar is falling behind…bit by bit...