by Ted Pedas
Youngstown State University Planetarium Lecturer
Feb 3, 1980
In case you haven't yet noticed, this month has an extra day. Yes, this is a leap year.
This once in a quadrennium observation ought to be of some small consolation to those who are doomed to an official birthday celebration only once every four years.
Invented more than 2,000 years ago, we cannot, however, deem the whole idea as a bust.
In the first place, without that extra day, the year would gradually crawl around the seasons until we would be celebrating Independence Day in Winter, and Christmas in July.
Leap Year the name given to a year consisting of 366 days is the result of our inability to devise a perfect calendar. Every fourth year we simply add an extra day to make up the hours that cannot be accommodated in a 365-day year.
The calendar is an artificial device set up by humans to expedite record keeping. We obviously can't push the Sun around when our artificial calendar gets out of whack, so we change the calendar to make it coincide with the Sun.
To be effective, a manmade calendar must correspond and keep in step with the seasons of the natural year the time it takes for the Earth to revolve once around the Sun.
The problem arises since the calendar year is 5 hours, 48 minutes and 46 seconds short of the solar year. Every four years this accumulates to nearly 24 hours.This period of time is then worked into the calendar by the addition of a leap year, or a year with an extra added day to take up that additional 24 hours.
If we did not stabilize this slight drifting of the calendar in the course of a few centuries, we would be marking the celebration of Easter in Winter, Christmas in Autumn, and Labor Day in the Spring.
The monumental problem of keeping the calendar on track with the seasons, dates back to the dawn of recorded history.
The Egyptians had perfected an excellent method of time reckoning based on the Sun, rather than the erratic cycles of the Moom. By Roman times, however, the calendar was found in a bewildering state. The Roman calendar had fallen into political abuse. No one could tell in advance how long the year was likely to be, since days were infrequently removed or added to lenghten or shorten the calendar and thus the service terms of certain political officials.
Rome had been following a calendar that first had 10 months of 304 days. This, of course, did not work well at all. A 12 month calendar of 355 days followed. This required the addition of a 13th month of varying lengths added every other year.
By Julius Caesar's time, the calendar was in a total state of confusion and getting worse all the time.
Caesar's alarm over the status of the Roman calendar resulted in his initiation of a sweeping reform which went into effect in 45 B.C.
On the advice of his astronomers, Caesar first devised a plan whereby the months of theyear would be brought back in proper step with the seasons. Among other adjustments, it was necessary to lengthen the year of 46 B.C. to a total of 445 days. In this manner, spring of the year 45 B.C. would come at the proper season in March.
So drastic was this measure, that the year 46 B.C. is often referred to as the year of confusion.
The Julian reform also introduced the concept of the leap year into the calendar.
Caesar's astronomer determined that the Earth does not spin on its axis in an exact number ot times during one revolution about the Sun. He calculated the true length of the year tobe 365 and one quarter days, or 365 days and 6 hours. The extra quarter of a day, or six hours, could not be included in the year until it amounted to a whole day. Therefore, Caesar decreeed that the Roman year would consist of 365 days in a normal year but that every fourth year would contain 366 days.
Caesar's reform marked a noble achievement in the history of our calendar but it was still not a perfect system of time-reckoning.
Since it takes the Earth 365 days, 5 hours, and 48 minutes to orbit once around the SUN and not an even 365 and one quarter the average year in the Julian calendar was 11 minutes and 14 seconds or .0078 days too long.
This slight annual error is not detectable in the course of a few years. But it adds up to one whole day in every 128 years a calendar drift of three days every 385 years.
By the 15th Century, the Julian calaendar was in error by 11 days. The vernal equinox the first day of spring was then falling on March 11 instead of March 25 as it did in the days of Caesar.
In an effort to bring the calendar year in accordance with the seasons once again, Pope Gregory the XIII decreed that the day after Octover 4, 1582, would be followed by October 15. The dropping of 10 days from the calendar made the Vernal Equinox fall on March 21.
In order to prevent further errors, Pope Gregory also decreed that centesimal years (1800, 1900, 2000,etc.) would be leap years, only if they could be exactly divided by 400.
In this revised leap year plan, the year 2000 will contain 366 days ⮏ but the century years 2100, 2200, and 2300 will have only 365 days. The elimination of three leap years every 400 years leaves the calendar a mere 26 seconds out of step with the natural seasons or one whole day every 3,323 years.
by Ted Pedas
Youngstown State University Planetarium Lecturer
Feb 10, 1980
How long is one day? A simple question the simple answer to which would be 24 yours, right?
Let's try another one. How long is one year? You say 365 days? Well, that's two strikes.
But no. Some of you may protest. Some of you think that you are correct. After all, everyone knows there are 24 hours in a day look at any clock. And any calendar will tell you that there are 365 days in a year.
But this is only because everyone has been conditioned to this ever since grade school.
The truth is that our methods of time-keeping are totally artificial they are simplified, man-made systems which attempt to round-off the cycles of nature.
In reality, for example, the Earth's natural period of rotation the time it takes for our planet to spin once on its axis is 23 hours, 56 minutes and 4 seconds.
A case in point. From here in Youngstown, if you were to notice that some particular star tonight was directly overhead, the time it would take for that star to appear to circle around and return to the exact same place in the sky would be 23 hours, 56 minutes and 4 seconds or one period of Earth rotation.
The stars, as we know, are extremely distant many light years away. So they may be regarded as fixed reference points from our rotating Earth.
But our planet doesn't sit still while it spins it also orbits around the Sun. The Sun, however, is much closer than the other stars, so as the Earth moves around it, the Sun will appear to slowly drift to change position with respect to the more distant background stars.
So while the Earth's natural rotation period will return the nightly stars to the same place, it is insufficient to bring the Sun back to the same place in the sky as on the previous day an extra 3 minutes and 56 seconds of Earth rotation is required to return the Sun go the same position in the sky every day.
In common usage then, a day is 24 hours long. But scientists measure the day as being one period of Earth rotation. This would be impractical in everyday life, however, since it would not only be difficult to construct a clock to easily record 23 hours, 56 minutes and 4 seconds of time but, that gradual drifting of the Sun around the sky would soon accumulate to the point that we would be eating our lunches with the stars out and the Sun would be high overhead when the clock reads midnight.
But, we have come to base the routine of our daily lives on the Sun and its position in the sky, so for practical purposes we have opted to let the Earth rotate that extra 3 minutes and 56 seconds so that the Sun will remain in step always being in the right place at the right time. (Daylight Saving Time is another story.)
So to keep the Sun high overhead year round we take the Earth's natural period of rotation 23 hours, 56 minutes, 4 seconds to establish the artificial 24 hour day with 60 minutes in each hour, and 60 seconds in each minute.
Now let us consider the actual length of the year. The time it takes the Earth to revolve once abut the Sun so that the Sun appears to drift around the sky and return to the same position with respect to the background of stars is 365 days, 6 hours, 9 minutes and 9.5 seconds. This is known as the sidereal, or star year.
But again, we choose an arbitrary point to measure the year. The path of the Sun's apparant motion through the sky is called the ecliptic. It is the position of the Sun on the ecliptic that determines the time of year.
Now if the ecliptic were fixed in relation to the background stars, our solar year would be the same as the sidereal year mentioned above. The Earth, however, wobbles as it rotates on its axis, and this causes the ecliptic to crawl around the sky by a small amount each year.
Therefore, the Sun in its annual apparent movement, completes its journey around the sky 20 minutes sooner than it returns to its original starting place with respect to the stars. So our standard solar year is measured as being 365 days, 5 hours, 48 minutes and 46 seconds long.
So, because we like to get up at sunrise, eat lunch at noon, and hit the sack at sunset we have a nice round 24 hour day. And because we like sunshine in July and snow at Christmas we end up with a year of 365 and a quarter days.
As a result of our inability to establish a perfect calendar to keep step with the exacting cycles of nature, we then have to hold that quarter day aside until it adds up to a complete day, one every four years. At those times, designated leap years we tack that additional day on to the end of February.
A final question. Why then? Why not in some other month? And again an arbitrary decision. Since the other months have more days already, and February usually has only 28 it seems, better to put it there. After all, it would mess up things for many bookkeepers if they had to wait till the 32nd of some month to send out bills.
E-mail: Ted Pedas