“Much Ado About Time …” Part I

For us scientists, time is an important part of our general work.  For example, how long is a particular chemical reaction?  What’s the time required for the flowering of a rare orchid?  How much time does it take to travel to the Moon and back again to Earth?  What’s the gestation period for elephants?  How many weeks does it take a wood thrush to migrate in the spring from Panama to the Roanoke Valley?  (Distance, too, is an important consideration for us scientists.  The average migrating distance for the wood thrush, for instance, is 2200 kilometers between its wintering and breeding grounds!)  Why is a solar year different from a lunar year?  And, of vital importance, how long will my coffee take to brew in the morning?  Charles Darwin, the quintessential hero in the sciences, even commented once, “A man who dares to waste one hour of time has not discovered the value of life.”  So time is an ever-important part of our profession as scientists: whether in the timing of an experiment or the focus of our lives.  Time, like a mind, is a terrible thing to waste.

The problem with time is its relevance.  Or do I mean its absoluteness?

I guess the question about time was answered by Einstein about a century ago.  According to his theory of special relativity, time is not an absolute as Newton claimed.  With the proper technology, one person may experience an interval of several days while another person simultaneously experiences only moments.  If the same two people meet up again, they both will have aged at different rates.  According to another brilliant physicist, Richard Feynman, time is simply a direction in space.  Time is relative to which direction in space one travels.  Whew.

All that aside for the moment, I’d like to explore one measure of time called a calendar, especially since we just celebrated the Spring Equinox and the religious observances of Passover and Easter.  Calendars are important tools for all of us, whether we’re scientists or not.  If you’ve ever forgotten your wedding anniversary or your best friend’s birthday, you know you can get into a whole heap of trouble for overlooking calendar events.

Let’s begin with the difference between astronomical calendars: a solar calendar and a lunar calendar.  For ages, cultures around the world have used either or both.  A solar month (also called a sidereal month) is the time taken by the Moon to complete one full revolution around the Earth with respect to the background stars.  Because the Earth is constantly moving along its orbit around the Sun, however, the Moon must travel slightly more than 360 degrees to get from one new moon to the next.  Thus, the lunar month is longer than the sidereal month (29.53 days and 27.32 days, respectively).  The only purely lunar calendar in use today is the Islamic calendar whose year always consists of 12 lunar months.  However, since it’s not linked to the seasons, the calendar drifts each solar year by 11 or 12 days, returning to its original position every 33 years.  Most lunar calendars are, in fact, lunisolar calendars (e.g., Hebrew, Hindu, and Chinese calendars) because they are linked to the seasons. Since there are about 12 lunations in a solar year, this period (354.36 days) is referred to as a lunar year but corresponds to 13 sidereal months.  Just think: people have been observing the heavens closely for millennia, figuring out all these affairs among the Earth, Moon, and stars long before our fancy 21st-century technologies!  Whew.  Ah, if only my students were as observant!

Next we have to recognize two good ole’ boys in our history of time: Julius Caesar and Pope Gregory XIII.  Julius Caesar established a calendar in 46 BCE throughout his empire, fixing the length of year at 365 days and at 366 every fourth year: a smart business move toward standardization for this charismatic leader of millions.  Too bad Brutus finished him off on the Ides of March; what else might this 56-year-old have contrived if he had lived longer?  Pope Gregory worried about the gradual drift in the Julian calendar so he introduced a new one by papal decree in 1582.  For this new calendar, he reformed the old Julian device according to which an ordinary year consists of 365 days but with a leap year of 366 days every year whose number is exactly divisible by four except centenary years whose numbers are not exactly divisible by 400, as 1700, 1800, and 1900.  Accordingly, the last day of the Julian calendar was Thursday, 4 October 1582, followed by the next day, Friday, by the first day of the Gregorian calendar, 15 October 1582.  Wonder what happened to all the plans for birthday parties and wedding anniversaries on Friday, 5 October?

With this as background, we’ll take a look at Passover and Easter in Part II of this essay.  For those who can’t wait, here’s a short homework assignment: try to figure out how the Vernal Equinox is linked to these great observances.  Be ye warned!  Not everyone agrees!