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Sunday, May 31, 2009

Banned Advertisement :- Pepsi Vs Coca Cola Part - 2

Check Out The Second Part Of Banned Advertisements Of Never Ending Fight Of Two World Leaders In Soft Drink

Pepsi Vs Coca Cola

Banned Advertisement :- Pepsi Vs Coca Cola Part - 1

Check Out The First Part Of Banned Advertisements Of Never Ending Fight Of two World Leaders In Soft Drink

Pepsi Vs Coca Cola

Thursday, May 28, 2009

Twirl Once In The Mirror

This is exactly why you should always, ALWAYS...
twirl once in front of the mirror before leaving the house.
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Saturday, May 23, 2009

History Of Calenders Part - 5

Countries` Calendar Reform
The Election: 1. An Election Entertainment. By William Hogarth (1754)
One of the most hotly contested issues of the 1754 election was calendar reform. The orange banner on the left of Hogarth’s painting carries a protest against the Gregorian calendar. It reads, "Give us our eleven days."
In most societies a calendar reform is an extraordinary event. Adoption of a calendar depends on the forcefulness with which it is introduced and on the willingness of society to accept it. For example, the acceptance of the Gregorian calendar as a worldwide standard spanned more than three centuries.
The legal code of the United States does not specify an official national calendar. Use of the Gregorian calendar in the United States stems from an Act of Parliament of the United Kingdom in 1751, which specified use of the Gregorian calendar in England and its colonies. However, its adoption in the United Kingdom and other countries was fraught with confusion, controversy, and even violence (Bates, 1952; Gingerich, 1983; Hoskin, 1983). It also had a deeper cultural impact through the disruption of traditional festivals and calendrical practices (MacNeill, 1982).

When did countries change from Julian to Gregorian calendars?

The papal bull of February 1582 decreed that 10 days should be dropped from October 1582 so that 15 October should follow immediately after 4 October, and from then on the reformed calendar should be used.
This was observed in Italy, Poland, Portugal, and Spain. Other Catholic countries followed shortly after, but Protestant countries were reluctant to change, and the Greek orthodox countries didn’t change until the start of the 1900s.
Changes in the 1500s required 10 days to be dropped. Changes in the 1600s required 10 days to be dropped. Changes in the 1700s required 11 days to be dropped. Changes in the 1800s required 12 days to be dropped. Changes in the 1900s required 13 days to be dropped. For example, when Soviet Russia undertook its calendar reform in February 1918, they moved from the Julian calendar to the Gregorian. This move resulted in a loss of 13 days, so that February 1, 1918, became February 14.
The following list contains the dates for changes in a number of countries. It is very strange that in many cases there seems to be some doubt among authorities about what the correct days are. Different sources give very different dates in some cases. The list below does not include all the different opinions about when the change took place.
→ See the British Calendar Act of 1751.
Albania:December 1912
Austria:Different regions on different dates
Brixen, Salzburg and Tyrol:
5 Oct 1583 was followed by 16 Oct 1583
Carinthia and Styria:
14 Dec 1583 was followed by 25 Dec 1583
See also Czechoslovakia and Hungary
Belgium:Then part of the Netherlands
Bulgaria:31 Mar 1916 was followed by 14 Apr 1916
Canada:Different areas changed at different times।
Newfoundland and Hudson Bay coast:
2 Sep 1752 was followed by 14 Sep 1752
Mainland Nova Scotia:
Gregorian 1605 - 13 Oct 1710
Julian 2 Oct 1710 - 2 Sep 1752
Gregorian since 14 Sep 1752
Rest of Canada:
Gregorian from first European settlement
China:The Gregorian calendar replaced the Chinese calendar in either 1912 or 1929 (depending on which authorities you believe)।
Czechoslovakia (i.e. Bohemia and Moravia):6 Jan 1584 was followed by 17 Jan 1584
Denmark (including Norway):18 Feb 1700 was followed by 1 Mar 1700
31 Jan 1918 was followed by 14 Feb 1918
Finland:Then part of Sweden. (Note, however, that Finland later became part of Russia, which then still used the Julian calendar. The Gregorian calendar remained official in Finland, but some use of the Julian calendar was made.)
France:9 Dec 1582 was followed by 20 Dec 1582
Alsace: 5 Feb 1682 was followed by 16 Feb 1682
Lorraine: 16 Feb 1760 was followed by 28 Feb 1760
Strasbourg: February 1682
Germany:Different states on different dates:
Catholic states on various dates in 1583-1585
Prussia: 22 Aug 1610 was followed by 2 Sep 1610
Protestant states: 18 Feb 1700 was followed by 1 Mar 1700
(Many local variations)
Great Britain and Dominions:2 Sep 1752 was followed by 14 Sep 1752
Greece:9 Mar 1924 was followed by 23 Mar 1924
(Some sources say 1916 and 1920)
Hungary:21 Oct 1587 was followed by 1 Nov 1587
Ireland:See Great Britain
Italy:4 Oct 1582 was followed by 15 Oct 1582
Japan:The Gregorian calendar was introduced to supplement the traditional Japanese calendar on 1 Jan 1873.
Latvia:During German occupation 1915 to 1918
Luxemburg:14 Dec 1582 was followed by 25 Dec 1582
Netherlands (including Belgium):Zeeland, Brabrant, and the "Staten Generaal":
14 Dec 1582 was followed by 25 Dec 1582
Holland: 1 Jan 1583 was followed by 12 Jan 1583
Limburg and the southern provinces (currently Belgium):
20 Dec 1582 was followed by 31 Dec 1582
21 Dec 1582 was followed by 1 Jan 1583
10 Feb 1583 was followed by 21 Feb 1583
Went back to Julian in the summer of 1594
31 Dec 1700 was followed by 12 Jan 1701
30 Jun 1700 was followed by 12 Jul 1700
Utrecht and Overijssel:
30 Nov 1700 was followed by 12 Dec 1700
31 Dec 1700 was followed by 12 Jan 1701
30 Apr 1701 was followed by 12 May 1701
Norway:Then part of Denmark.
Poland:4 Oct 1582 was followed by 15 Oct 1582
Portugal:4 Oct 1582 was followed by 15 Oct 1582
Romania:31 Mar 1919 was followed by 14 Apr 1919
(The Greek Orthodox parts of the country may have changed later)
Russia:31 Jan 1918 was followed by 14 Feb 1918
(In the eastern parts of the country the change may not have occured until 1920)
Scotland:See Great Britain.
Spain:4 Oct 1582 was followed by 15 Oct 1582
Sweden (including Finland):17 Feb 1753 was followed by 1 Mar 1753 (see note below)
Switzerland:Catholic cantons: 1583, 1584 or 1597
Protestant cantons:
31 Dec 1700 was followed by 12 Jan 1701
(Many local variations)
Turkey:Gregorian calendar introduced 1 Jan 1927
USA:Different areas changed at different times.
Along the Eastern seaboard: With Great Britain in 1752.
Mississippi valley: With France in 1582.
Texas, Florida, California, Nevada, Arizona, New Mexico:
With Spain in 1582
Washington, Oregon: With Britain in 1752.
Alaska: October 1867 when Alaska became part of the USA.
Wales:See Great Britain
Sweden has a curious history. Sweden decided to make a gradual change from the Julian to the Gregorian calendar. By dropping every leap year from 1700 through 1740 the eleven superfluous days would be omitted and from 1 Mar 1740 they would be in sync with the Gregorian calendar. (But in the meantime they would be in sync with nobody!)
So 1700 (which should have been a leap year in the Julian calendar) was not a leap year in Sweden. However, by mistake 1704 and 1708 became leap years. This left Sweden out of synchronisation with both the Julian and the Gregorian world, so they decided to go back to the Julian calendar. In order to do this, they inserted an extra day in 1712, making that year a double leap year! So in 1712, February had 30 days in Sweden.
Later, in 1753, Sweden changed to the Gregorian calendar by dropping 11 days like everyone else.

Thursday, May 14, 2009

History Of Calenders Part - 4

When did the 3rd millennium start?

The first millennium started in AD 1, so the millennia are counted in this manner:
1st millennium: 1-1000
2nd millennium: 1001-2000
3rd millennium: 2001-3000
Thus, the 3rd millennium and, similarly, the 21st century started on 1 Jan 2001.
This is the cause of some heated debate, especially since some dictionaries and encyclopedias say that a century starts in years that end in 00. Furthermore, the change 1999/2000 is obviously much more spectacular than the change 2000/2001.
Let us propose a few compromises:
Any 100-year period is a century. Therefore the period from 23 June 2004 to 22 June 2104 is a century. So please feel free to celebrate the start of a century any day you like!
Although the 20th century started in 1901, the 1900s started in 1900. Similarly, the 21st century started in 2001, but the 2000s started in 2000.

What do A.D., B.C., C.E., and B.C.E. stand for?

Years before the birth of Christ are in English traditionally identified using the abbreviation B.C. ("Before Christ").
Years after the birth of Christ are traditionally identified using the Latin abbreviation AD ("Anno Domini", that is, "In the Year of the Lord").
Some people, who want to avoid the reference to Christ that is implied in these terms, prefer the abbreviations BCE ("Before the Common Era" or "Before the Christian Era") and CE ("Common Era" or "Christian Era").

Historical eras & chronology

The calendars described in this exhibit, except for the Chinese calendar, have counts of years from initial epochs. In the case of the Chinese calendar and some calendars not included here, years are counted in cycles, with no particular cycle specified as the first cycle. Some cultures eschew year counts altogether but name each year after an event that characterized the year. However, a count of years from an initial epoch is the most successful way of maintaining a consistent chronology. Whether this epoch is associated with an historical or legendary event, it must be tied to a sequence of recorded historical events.
This is illustrated by the adoption of the birth of Christ as the initial epoch of the Christian calendar. This epoch was established by the sixth-century scholar Dionysius Exiguus, who was compiling a table of dates of Easter. An existing table covered the nineteen-year period denoted 228-247, where years were counted from the beginning of the reign of the Roman emperor Diocletian. Dionysius continued the table for a nineteen-year period, which he designated Anni Domini Nostri Jesu Christi 532-550. Thus, Dionysius’ Anno Domini 532 is equivalent to Anno Diocletian 248. In this way a correspondence was established between the new Christian Era and an existing system associated with historical records. What Dionysius did not do is establish an accurate date for the birth of Christ. Although scholars generally believe that Christ was born some years before A.D. 1, the historical evidence is too sketchy to allow a definitive dating.
Given an initial epoch, one must consider how to record preceding dates. Bede, the eighth-century English historian, began the practice of counting years backward from A.D. 1 (see Colgrave and Mynors, 1969). In this system, the year A.D. 1 is preceded by the year 1 B.C.E., without an intervening year 0. Because of the numerical discontinuity, this "historical" system is cumbersome for comparing ancient and modern dates. Today, astronomers use +1 to designate A.D. 1. Then +1 is naturally preceded by year 0, which is preceded by year -1. Since the use of negative numbers developed slowly in Europe, this "astronomical" system of dating was delayed until the eighteenth century, when it was introduced by the astronomer Jacques Cassini (Cassini, 1740).
Even as use of Dionysius’ Christian Era became common in ecclesiastical writings of the Middle Ages, traditional dating from regnal years continued in civil use. In the sixteenth century, Joseph Justus Scaliger tried to resolve the patchwork of historical eras by placing everything on a single system (Scaliger, 1583). Instead of introducing negative year counts, he sought an initial epoch in advance of any historical record. His numerological approach utilized three calendrical cycles: the 28-year solar cycle, the nineteen-year cycle of Golden Numbers, and the fifteen-year indiction cycle. The solar cycle is the period after which weekdays and calendar dates repeat in the Julian calendar. The cycle of Golden Numbers is the period after which moon phases repeat (approximately) on the same calendar dates. The indiction cycle was a Roman tax cycle. Scaliger could therefore characterize a year by the combination of numbers (S,G,I), where S runs from 1 through 28, G from 1 through 19, and I from 1 through 15. Scaliger noted that a given combination would recur after 7980 (= 28*19*15) years. He called this a Julian Period, because it was based on the Julian calendar year. For his initial epoch Scaliger chose the year in which S, G, and I were all equal to 1. He knew that the year 1 B.C.E. was characterized by the number 9 of the colar cycle, by the Golden Number 1, and by the number 3 of the indiction cycle, i.e., (9,1,3). He found that the combination (1,1,1) occurred in 4713 B.C.E. or, as astronomers now say, -4712. This serves as year 1 of Scaliger’s Julian Period. It was later adopted as the initial epoch for the Julian day numbers.

ISO 8601

What date format does the Standard mandate?

There are three basic formats: Calendar date, ordinal date, and week date.
A calendar date should be written as a 4-digit year number, followed by a 2-digit month number, followed by a 2-digit day number. Thus, for example, 2 August 1953 may be written:
19530802 or 1953-08-02
An ordinal date should be written as a 4-digit year number, followed by a 3-digit number indicating the number of the day within the year. Thus, for example, 2 August 1953 may be written:
1953214 or 1953-214
2 August is the 214th day of a non-leap year.
A week date should be written as a 4-digit year number, followed by a W, followed by a 2-digit week number followed by a 1-digit week day number (1=Monday, 2=Tuesday, ..., 7=Sunday). The week number is defined in section 7.7. Thus, for example, 2 August 1953 may be written:
1953W317 or 1953-W31-7
2 August was the Sunday of week 31 of 1953.
In all the examples above, the hyphens are optional.
Note that you must always write all the digits. Thus the year 47 must be written as 0047.

What time format does the Standard mandate?

A 24-hour clock must be used. A time is written as a 2-digit hour, followed by a 2-digit minute, followed by a 2-digit second, followed by a comma, followed by a number of digits indicating a fraction of a second. For example, thus:
140812,35 or 14:08:12,35
The fraction, the seconds, and the minutes may be omitted if less accuracy is required:
140812 or 14:08:12
1408 or 14:08
In all the examples above, the colons are optional. The comma may be replaced by a period (.), but this is not recommended.
The time may optionally be followed by a time zone indication. For UTC, the time zone indication is the letter Z. For other time zones, the indication is a plus or minus followed by the time difference to UTC (plus for times east of Greenwich, minus for times west of Greenwich). For example:
1130Z (11:30 UTC)
1130+0430 (11:30, at a location 4 and a half hours ahead of UTC)
1130-05 (11:30, at a location 5 hours behind of UTC)

What if I want to specify both a date and a time?

Date and time indications can be strung together by putting the letter T between them. For example, ten minutes to 7 p.m. on 2 August 1953 may be written as:
19530802T185000 or 1953-08-02T18:50:00

What format does the Standard mandate for a time interval?

There are several to choose from. A time interval can be specified as a starting time and an ending time or as a duration together with either a starting time and an ending time.
There are too many details to cover, so here are a few examples:
Using starting time and ending time:
Using starting time and duration:
This last example should be read as the time interval starting on 12 March 1927 at 08:04 and lasting for 1 year, 4 months, 12 days, 6 hours, 30 minutes, and 9 seconds. The letter P following the slash indicates that a duration follows.

Can I write BC dates and dates after the year 9999 using ISO 8601?

Yes, you can.
The year 1 BC must be written as 0000. The year 2 BC must be written as -0001, the year 3 BC must be written as -0002 etc.
Years of more than 4 digits must be written with an initial plus sign. Thus the year AD 10000 must be written as +10000.

Can I write dates in the Julian calendar using ISO 8601?

No. The Standard requires that the Gregorian calendar be used for all dates. Dates before the introduction of the Gregorian calendar are written using the proleptic Gregorian calendar. This is one of the few places where the proleptic Gregorian calendar is used.
Thus the Julian date 12 March 826 must be written as 0826-03-16, because its equivalent date in the Gregorian calendar is 16 March.

Does the Standard define the Gregorian calendar?

Yes, ISO 8601 specifies how the Gregorian calendar works. The specification is completely compatible with the calendar specified by Pope Gregory XIII in 1582, except that ISO 8601 does not concern itself with the calculation of Easter.
However, the calendar reference point used by the Standard is not Christ’s birth but the date on which the metric convention ("Convention du Metre") was signed in Paris. The Standard defines that date to be 20 May 1875.
Similarly, the reference point of the week cycles is 1 January 2000, which is defined to be a Saturday.
Of course, these reference points are also completely compatible with common usage.

What does the Standard say about the week?

According to ISO 8601, Monday is the first day of the week.
Each week has a number. A week that lies partly in one year and partly in another is assigned a number in the year in which most of its days lie. The Standard specifies this by saying that week 1 of any year is the week that includes the first Thursday of that year.

Why are ISO 8601 dates not used in this Calendar FAQ?

The Standard specifies how to write dates using only numbers. The Standard explicitly does not cover the cases where dates are written using words (such as January, February, etc.). In fact, the Standard itself makes frequent use of dates such as "20 May 1875" and "15 October 1582".
In other words, ISO 8601 helps people with data communication where it is natural to use all-number dates. In everyday language (spoken and written) we are free to use the terms we like best.

Where can I get the Standard?

If you are looking for a free copy somewhere on the internet, forget it! ISO makes money from selling copies of their standards.
ISO 8601:2004 can be bought from ISO at http://www.iso.ch. It is very expensive. The last time we checked, the price was 126 Swiss Francs (about U.S. $103) for a 33 page document.
Your local library may be able to find a copy for you.

Wednesday, May 13, 2009

History Of Calenders Part - 3

Definitions of Our Year
Pope Gregory XIII
Inter Gravissimas
The calendar used throughout the world today is the Gregorian calendar. It is sometimes called a "Christian" calendar, and additional historic information about this calendar, and its precursor, the Julian calendar, are available in the history of the Cristian calendar section.

The Gregorian calendar is the one commonly used today. It was proposed by Aloysius Lilius, a physician from Naples, and adopted by Pope Gregory XIII (portrait above right) in accordance with instructions from the Council of Trent (1545-1563) to correct for errors in the older Julian Calendar. It was decreed by Pope Gregory XIII in a papal bull, Inter Gravissimas, on February 24, 1582 (shown at right). This bull is named "Inter Gravissimas" after its first two words.
In the Gregorian calendar, the tropical year is approximated as 365 97/400 days = 365.2425 days. Thus it takes approximately 3300 years for the tropical year to shift one day with respect to the Gregorian calendar.
The approximation 365 97/400 is achieved by having 97 leap years every 400 years.

The Internatinal Organization for Standardization, ISO, has published a standard on how to write dates, times, and time intervals. This standard is known as ISO 8601. The text below refers to the third edition of that standard, which was published on 1 December 2004. Its title is: ISO 8601:2004, "Data elements and interchange formats - Information interchange - Representation of dates and times."

What years are leap years?

Leap years were introduced to keep New Year’s Day on autumnal equinox. But this turned out to be difficult to handle, because equinox is not completely simple to predict.
In fact, the first decree implementing the calendar (5 Oct 1793) contained two contradictory rules, as it stated that:
  • the first day of each year would be that of the autmunal equinox
  • every 4th year would be a leap year
In practice, the first calendars were based on the equinoxial condition.
To remove the confusion, a rule similar to the one used in the Gregorian Calendar (including a 4000 year rule) was proposed by the calendar’s author, Gilbert Romme, but his proposal ran into political problems.
In short, during the time when the French Revolutionary Calendar was in use, the the following years were leap years: 3, 7, and 11.

Is there a 4000-year rule?

It has been suggested (by the astronomer John Herschel (1792-1871) among others) that a better approximation to the length of the tropical year would be 365 969/4000 days = 365.24225 days. This would dictate 969 leap years every 4000 years, rather than the 970 leap years mandated by the Gregorian calendar. This could be achieved by dropping one leap year from the Gregorian calendar every 4000 years, which would make years divisible by 4000 non-leap years.
This rule has, however, not been officially adopted.

Do the Greeks do it differently?

When the Orthodox church in Greece finally decided to switch to the Gregorian calendar in the 1920s, they tried to improve on the Gregorian leap year rules, replacing the "divisible by 400" rule by the following:
Every year which when divided by 900 leaves a remainder of 200 or 600 is a leap year.
This makes 1900, 2100, 2200, 2300, 2500, 2600, 2700, 2800 non-leap years, whereas 2000, 2400, and 2900 are leap years. This will not create a conflict with the rest of the world until the year 2800.
This rule gives 218 leap years every 900 years, which gives us an average year of 365 218/900 days = 365.24222 days, which is certainly more accurate than the official Gregorian number of 365.2425 days.
However, this rule is not official in Greece.

What day is the leap day?

It is 24 February!
Weird? Yes! The explanation is related to the Roman calendar.
From a numerical point of view, of course 29 February is the extra day. But from the point of view of celebration of feast days, the following correspondence between days in leap years and non-leap years has traditionally been used:
Non-leap yearLeap year
22 February22 February
23 February23 February
24 February (extra day)
24 February25 February
25 February26 February
26 February27 February
27 February28 February
28 February29 February
For example, the feast of St. Leander has been celebrated on 27 February in non-leap years and on 28 February in leap years.
Many countries are gradually changing the leap day from the 24th to the 29th. This affects countries such as Sweden and Austria that celebrate "name days" (i.e., each day is associated with a name).

What is the Solar Cycle?

In the Julian calendar the relationship between the days of the week and the dates of the year is repeated in cycles of 28 years. In the Gregorian calendar this is still true for periods that do not cross years that are divisible by 100 but not by 400.
A period of 28 years is called a Solar Cycle. The Solar Number of a year is found as:
Solar Number = (year + 8) mod 28 + 1
In the Julian calendar there is a one-to-one relationship between the Solar Number and the day on which a particular date falls.
(The leap year cycle of the Gregorian calendar is 400 years, which is 146,097 days, which curiously enough is a multiple of 7. So in the Gregorian calendar the equivalent of the "Solar Cycle" would be 400 years, not 7 x 400 = 2800 years as one might be tempted to believe.)

What is the Dominical Letter?

Each ordinary (non-leap) year is assigned a letter in the range A to G which describes what days of the year are Sundays. This letter is called the "Dominical Letter" ("Sunday Letter") of the year.
It works in this manner: Assign the letter A to 1 January, B to 2 Jan, C to 3 Jan, ... G to 7 Jan, A to 8 Jan, B to 9 Jan, and so on, using the letters A to G and omitting the leap day.
In a year with Dominical Letter A, all days marked A are Sundays. In a year with Dominical Letter B, all days marked B are Sundays. And so on.
Leap years have two Dominical Letters, one which is used from the start of January until the leap day, and another one which is used for the rest of the year.
The Dominical Letter of 2006 is A. The Dominical Letters of 2008 will be F and E.

When can I reuse my 1992 calendar?

Let us first assume that you are only interested in which dates fall on which days of the week; you are not interested in the dates for Easter and other irregular holidays.
Let us further confine ourselves to the years 1901-2099.
With these restrictions, the answer is as follows:
  • If year X is a leap year, you can reuse its calendar in year X+28.
  • If year X is the first year after a leap year, you can reuse its calendar in years X+6, X+17, and X+28.
  • If year X is the second year after a leap year, you can reuse its calendar in years X+11, X+17, and X+28.
  • If year X is the third year after a leap year, you can reuse its calendar in years X+11, X+22, and X+28.
Note that the expression X+28 occurs in all four items above. So you can always reuse your calendar every 28 years.
But if you also want your calendar’s indication of Easter and other Christian holidays to be correct, the rules are far too complex to be put to a simple formula. Sometimes calendars can be reused after just six years. For example, the calendars for the years 1981 and 1987 are identical, even when it comes to the date for Easter. But sometimes a very long time can pass before a calendar can be reused; if you happen to have a calendar from 1940, you won’t be able to reuse it until the year 5280!

What is the correct way to write dates?

The answer to this question depends on what you mean by "correct." Different countries have different customs.
In the U.S.A. a month-day-year format is common:
12/25/1998 or 12-25-1998 |
Most other countries use a day-month-year format, such as:
25.12.1998 or 25/12/1998 or 25/12-1998 or 25.XII.1998
International standard ISO-8601 mandates a year-month-day format, namely either
1998-12-25 or 19981225.
In all of these systems, the first two digits of the year are frequently omitted:
25.12.98 or 12/25/98 or 98-12-25
However, although the last form is frequently seen, it is not allowed by the ISO standard.
This confusion leads to misunderstandings. What is 02-03-04? To most people it is 2 Mar 2004; to an American it is 3 Feb 2004; and to a person using the international standard it could be 4 Mar 2002 (although a year specified with only two digits does not conform to the ISO standard).
If you want to be sure that people understand you, you should:
  • write the month with letters instead of numbers, and
  • write the years as 4-digit numbers.

How does one count years?

In about C.E. 523, the papal chancellor, Bonifatius, asked a monk by the name of Dionysius Exiguus to devise a way to implement the rules from the Nicean council (the so-called "Alexandrine Rules") for general use.
Dionysius Exiguus (in English known as Denis the Little) was a monk from Scythia, he was a canon in the Roman curia, and his assignment was to prepare calculations of the dates of Easter. At that time it was customary to count years since the reign of emperor Diocletian; but in his calculations Dionysius chose to number the years since the birth of Christ, rather than honour the persecutor Diocletian.
Dionysius (wrongly) fixed Jesus’ birth with respect to Diocletian’s reign in such a manner that it falls on 25 December 753 AUC (ab urbe condita, i.e., since the founding of Rome), thus making the current era start with C.E. 1 on 1 January 754 AUC.
How Dionysius established the year of Christ’s birth is not known (see History of our Calendar for a couple of theories). Jesus was born under the reign of king Herod the Great, who died in 750 AUC, which means that Jesus could have been born no later than that year. Dionysius’ calculations were disputed at a very early stage.
When people started dating years before 754 AUC using the term "Before Christ," they let the year 1 B.C.E. immediately precede C.E. 1 with no intervening year zero.
Note, however, that astronomers frequently use another way of numbering the years B.C.E. Instead of 1 B.C.E. they use 0, instead of 2 B.C.E. they use -1, instead of 3 B.C.E. they use -2, etc.
The earliest uses of BC dating are found in the works of the Venerable Bede (673-735).
In this section we have used C.E. 1 = 754 AUC. This is the most likely equivalence between the two systems. However, some authorities state that C.E. 1 = 753 AUC or 755 AUC. This confusion is not a modern one, it appears that even the Romans were in some doubt about how to count the years since the founding of Rome.


Tuesday, May 12, 2009

History of Calenders Part -2

A month of moons
With this interactive moon phase calendar, you can choose a month and year and see why lunar months aren’t an exact match with calendar months.

May 2009

Choose Month and Year:
First Quarter Moon
First Quarter Moon
Waxing Gibbous Moon
Waxing Gibbous Moon
Waxing Gibbous Moon
Waxing Gibbous Moon
Waxing Gibbous Moon
Waxing Gibbous Moon
Full Moon
Waning Gibbous Moon
Waning Gibbous Moon
Waning Gibbous Moon
Waning Gibbous Moon
Waning Gibbous Moon
Waning Gibbous Moon
Waning Gibbous Moon
Last Quarter Moon
Waning Crescent Moon
Waning Crescent Moon
Waning Crescent Moon
Waning Crescent Moon
Waning Crescent Moon
Waning Crescent Moon
New Moon Crescent Moon
Waxing Crescent Moon
Waxing Crescent Moon
Waxing Crescent Moon
Waxing Crescent Moon
Waxing Crescent Moon
Waxing Crescent Moon
First Quarter Moon
For millennia, calendars were constructed according to the phases of the moon. We can only imagine what ancient astronomers thought as they scanned the night sky and saw the constantly changing appearance of this large celestial body.
Step outside! Keep track of the moon in your night sky, and chart the changes yourself. See our tips on how to chart the moon in the sky and explore the phases of the moon over the course of its 29.53-day cycle. In the process, you’ll discover why lunar months aren’t an exact match with calendar months.

History of Our Calendar
Pope Gregory XIII. Portrait by Lavinia Fontana
Pope Gregory XIII dedicated his papacy to implementing the recommendations of the Council of Trent. By the time he reformed the Julian calendar in 1582 (using the observations of Christopher Clavius and Johannes Kepler), it had drifted 10 days off course. To this day, most of the world uses his Gregorian calendar.

Before today’s Gregorian calendar was adopted, the older Julian calendar was used. It was admirably close to the actual length of the year, as it turns out, but the Julian calendar was not so perfect that it didn’t slowly shift off track over the following centuries. But, hundreds of years later, monks were the only ones with any free time for scholarly pursuits – and they were discouraged from thinking about the matter of "secular time" for any reason beyond figuring out when to observe Easter. In the Middle Ages, the study of the measure of time was first viewed as prying too deeply into God’s own affairs – and later thought of as a lowly, mechanical study, unworthy of serious contemplation.
As a result, it wasn’t until 1582, by which time Caesar’s calendar had drifted a full 10 days off course, that Pope Gregory XIII (1502 - 1585) finally reformed the Julian calendar. Ironically, by the time the Catholic church buckled under the weight of the scientific reasoning that pointed out the error, it had lost much of its power to implement the fix. Protestant tract writers responded to Gregory’s calendar by calling him the "Roman Antichrist" and claiming that its real purpose was to keep true Christians from worshiping on the correct days. The "new" calendar, as we know it today, was not adopted uniformly across Europe until well into the 18th century.

Has the year always started on 1 January?

In some ways, yes. When Julius Caesar introduced his calendar in 45 B.C.E., he made 1 January the start of the year, and it was always the date on which the Solar Number and the Golden Number were incremented.
However, the church didn’t like the wild parties that took place at the start of the new year, and in C.E. 567 the council of Tours declared that having the year start on 1 January was an ancient mistake that should be abolished.
Through the middle ages various New Year dates were used. If an ancient document refers to year X, it may mean any of 7 different periods in our present system:
1 Mar X to 28/29 Feb X+1
1 Jan X to 31 Dec X
1 Jan X-1 to 31 Dec X-1
25 Mar X-1 to 24 Mar X
25 Mar X to 24 Mar X+1
Saturday before Easter X to Friday before Easter X+1
25 Dec X-1 to 24 Dec X
Choosing the right interpretation of a year number is difficult, so much more as one country might use different systems for religious and civil needs.
The Byzantine Empire used a year starting on 1 Sep, but they didn’t count years since the birth of Christ, instead they counted years since the creation of the world which they dated to 1 September 5509 B.C.E.
Since about 1600 most countries have used 1 January as the first day of the year. Italy and England, however, did not make 1 January official until around 1750.
In England (but not Scotland) three different years were used:
The historical year, which started on 1 January.
The liturgical year, which started on the first Sunday in advent.
The civil year, which
from the 7th to the 12th century started on 25 December,
from the 12th century until 1751 started on 25 March,
from 1752 started on 1 January.
→ See the British Calendar Act of 1751.
It is sometimes claimed that having the year start on 1 January was part of the Gregorian calendar reform. This is not true. This myth has probably started because in 1752 England moved the start of the year to 1 January and also changed to the Gregorian calendar. But in most other countries the two events were not related. Scotland, for example, changed to the Gregorian calendar together with England in 1752, but they moved the start of the year to 1 January in 1600.

Then what about leap years?

If the year started on, for example, 1 March, two months later than our present year, when was the leap day inserted?
When it comes to determining if a year is a leap year, since AD 8 the Julian calendar has always had 48 months between two leap days. So, in a country using a year starting on 1 March, 1439 would have been a leap year, because their February 1439 would correspond to February 1440 in the January-based reckoning.

What is the origin of the names of the months?

A lot of languages, including English, use month names based on Latin. Their meaning is listed below. However, some languages (Czech and Polish, for example) use quite different names.
JanuaryJanuariusNamed after the god Janus.
FebruaryFebruariusNamed after Februa, the purification festival.
MarchMartiusNamed after the god Mars.
AprilAprilisNamed either after the goddess Aphrodite or the Latin word aperire, to open.
MayMaiusProbably named after the goddess Maia.
JuneJuniusProbably named after the goddess Juno.
JulyJuliusNamed after Julius Caesar in 44 B.C.E. Prior to that time its name was Quintilis from the word quintus, fifth, because it was the 5th month in the old Roman calendar.
AugustAugustusNamed after emperor Augustus in 8 B.C.E. Prior to that time the name was Sextilis from the word sextus, sixth, because it was the 6th month in the old Roman calendar.
SeptemberSeptemberFrom the word septem, seven, because it was the 7th month in the old Roman calendar.
OctoberOctoberFrom the word octo, eight, because it was the 8th month in the old Roman calendar.
NovemberNovemberFrom the word novem, nine, because it was the 9th month in the old Roman calendar.
DecemberDecemberFrom the word decem, ten, because it was the 10th month in the old Roman calendar.

How did Dionysius date Christ’s birth?

There are quite a few theories about this. And many of the theories are presented as if they were indisputable historical fact. The following are two theories that tend to be more accepted:
According to the Gospel of Luke (3:1 & 3:23) Jesus was "about thirty years old" shortly after "the fifteenth year of the reign of Tiberius Caesar." Tiberius became emperor in C.E. 14. If you combine these numbers you reach a birthyear for Jesus that is strikingly close to the beginning of our year reckoning. This may have been the basis for Dionysius’ calculations.
Dionysius’ original task was to calculate an Easter table. In the Julian calendar, the dates for Easter repeat every 532 years. The first year in Dionysius’ Easter tables is C.E. 532. Is it a coincidence that the number 532 appears twice here? Or did Dionysius perhaps fix Jesus’ birthyear so that his own Easter tables would start exactly at the beginning of the second Easter cycle after Jesus’ birth?

Was Jesus born in the year 0?

There are two reasons for this:
There is no year 0.
Jesus was born before 4 B.C.E.
The concept of a year "zero" is a modern myth (but a very popular one). In our calendar, C.E. 1 follows immediately after 1 B.C.E. with no intervening year zero. So a person who was born in 10 B.C.E. and died in C.E. 10, would have died at the age of 19, not 20.
Furthermore, as described in section 2.14, our year reckoning was established by Dionysius Exiguus in the 6th century. Dionysius let the year C.E. 1 start one week after what he believed to be Jesus’ birthday. But Dionysius’ calculations were wrong. The Gospel of Matthew tells us that Jesus was born under the reign of king Herod the Great, who died in 4 B.C.E.. It is likely that Jesus was actually born around 7 B.C.E.. The date of his birth is unknown; it may or may not be 25 December.

Why do the 9th thru 12th months have names that mean 7th, 8th, 9th and 10th?

September through December were the seventh through tenth months of a calendar used by the first Romans. Ancient historian and Greek biographer Plutarch, wrote in C.E. 75, about how they became displaced to two positions higher than their names would indicate.
Read excerpt of Plutarch’s essay.
Read more about the early Roman calendar.

Why does February have only 28 days?

January and February both date from about the time of Rome’s founding. They were added to a calendar that had been divided into ten month-like periods whose lengths varied from 20 to 35 or more days. A winter season was not included, so those period lengths are believed to have been intended to reflect growth stages of crops and cattle.
When introduced, January was given 29 days and put at the beginning of the calendar year. February was given 23 days and put at the end. Then, for an undetermined period shortly after Rome’s founding, months were said to have begun when a new moon was first sighted. At some later time, month lengths were separated from lunations and again became fixed. At that time, February’s original length was extended by five days which gave it a total of 28.

Monday, May 11, 2009

History of Calenders Part - 1

Our Year
Illuminations of Dante's Divine Comedy
Illuminations of Dante’s Divine Comedy by Giovanni di Paolo (15th century)
Dante and Beatrice reach the sun, shown as a golden wheel sending golden rays to the landscape below. The Sun, located in the middle of the orbs, with three lesser above and three below, like the heart in the middle of the body, or a wise king in the middle of his kingdom.
The calendar is based on three key astronomical events.
  • A day, which is the time from one sunrise to the next sunrise — one complete rotation of the Earth.
  • A year, which is approximately 365.24 days — one complete orbit of Earth around the Sun.
  • A month, which is approximately 29.53 days — one complete orbit of the Moon around the Earth.
Since these time spans are not easily divided, calendars have always been imperfect. Some were rooted in tradition, while others evolved as humankind gained a greater understanding of science and astronomy. Some calendars, like the Christian calendar (which is the primary calendar in use today) focused on the Earth’s orbit. Others, like the Islamic calendar, focused on the Moon’s orbit. Still others, like the Jewish calendar and Chinese calendar, combine both.

More details

Most calendars are based on astronomical events. From our perspective on Earth, the two most important astronomical objects are the Sun and the Moon, which is why their cycles are very important in the construction and understanding of calendars.
Our concept of a year is based on the earth’s motion around the sun. The time from one fixed point, such as a solstice or equinox, to the next is called a tropical year. Its length is currently 365.242190 days, but it varies. Around 1900 its length was 365.242196 days, and around 2100 it will be 365.242184 days. (This definition of the tropical year is not quite accurate; see astronomic issues for more details.)
Our concept of a month is based on the moon’s motion around the earth, although this connection has been broken in the calendar commonly used now. The time from one new moon to the next is called a synodic month, and its length is currently 29.5305889 days, but it varies. Around 1900 its length was 29.5305886 days, and around 2100 it will be 29.5305891 days.
Note that these numbers are averages. The actual length of a particular year may vary by several minutes due to the influence of the gravitational force from other planets. Similarly, the time between two new moons may vary by several hours due to a number of factors, including changes in the gravitational force from the sun, and the moon’s orbital inclination.
It is unfortunate that the length of the tropical year is not a multiple of the length of the synodic month. This means that with 12 months per year, the relationship between our month and the moon cannot be maintained.
However, 19 tropical years is 234.997 synodic months, which is very close to an integer. So every 19 years the phases of the moon fall on the same dates (if it were not for the skewness introduced by leap years). Nineteen years is called a Metonic cycle (after Meton, an astronomer from Athens in the 5th century B.C.E.).
So, to summarize: There are three important numbers to note:
A tropical year is 365.24219 days.
A synodic month is 29.53059 days.
19 tropical years is close to an integral number of synodic months.
The Christian calendar (Gregorian calendar) is based on the motion of the earth around the sun, while the months have no connection with the motion of the moon.
On the other hand, the Islamic calendar is based on the motion of the moon, while the year has no connection with the motion of the earth around the sun.
Finally, the Jewish calendar combines both, in that its years are linked to the motion of the earth around the sun, and its months are linked to the motion of the moon.

Astronomical Basis of Calendars
The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth). The complexity of calendars arises because these cycles of revolution do not comprise an integral number of days, and because astronomical cycles are neither constant nor perfectly commensurable with each other.

What are different measures of the year?

The tropical year is defined as the mean interval between vernal equinoxes; it corresponds to the cycle of the seasons. Our calendar year is linked to the tropical year as measured between two March equinoxes, as originally established by Caesar and Sosigenes. The following expression, based on the orbital elements of Laskar (1986), is used for calculating the length of the tropical year:
365.2421896698 - 0.00000615359 T - 7.29E-10 T2 + 2.64E-10 T3 (days)
where T = (JD - 2451545.0) / 36525 and JD is the Julian day number. However, the interval from a particular vernal equinox to the next may vary from this mean by several minutes.
Another kind of year is called the sidereal year, which is the time it takes the earth to orbit the sun. In the year 2000, the length of the Tropical Year = 365.24219 days, and the length of the Sidereal Year = 365.2564.
Meridan Line. S. Petronio, Bologna
Meridan Line. S. Petronio, Bologna
In this sun calendar, a hole in the ceiling of the cathedral projects a shaft of sunlight onto this bronze strip on the pavement below, which is engraved with the days of the year and signs of the zodiac.
Astronomical Clock. Prague, Czech Republic
The Prague Astronomical Clock, which dates back to the 15th century, features a background illustrating the Earth and sky; an hourly clock; curved lines that represent 1/12 of the time between sunrise and sunset, and a circle with zodiac signs. A small star illustrates the vernal equinox. Sidereal time can also be read.
The synodic month, the mean interval between conjunctions of the Moon and Sun, corresponds to the cycle of lunar phases. The following expression for the synodic month is based on the lunar theory of Chapront-Touze’ and Chapront (1988):
29.5305888531 + 0.00000021621 T - 3.64E-10 T2 (days).
Again T = (JD - 2451545.0)/36525 and JD is the Julian day number. Any particular phase cycle may vary from the mean by up to seven hours.
In the preceding formulas, T is measured in Julian centuries of Terrestrial Dynamical Time (TDT), which is independent of the variable rotation of the Earth. Thus, the lengths of the tropical year and synodic month are here defined in days of 86400 seconds of International Atomic Time (TAI).
From these formulas we see that the cycles change slowly with time. Furthermore, the formulas should not be considered to be absolute facts; they are the best approximations possible today. Therefore, a calendar year of an integral number of days cannot be perfectly synchronized to the tropical year. Approximate synchronization of calendar months with the lunar phases requires a complex sequence of months of 29 and 30 days. For convenience it is common to speak of a lunar year of twelve synodic months, or 354.36707 days.
Three distinct types of calendars have resulted from this situation. A solar calendar, of which the Gregorian calendar in its civil usage is an example, is designed to maintain synchrony with the tropical year. To do so, days are intercalated (forming leap years) to increase the average length of the calendar year. A lunar calendar, such as the Islamic calendar, follows the lunar phase cycle without regard for the tropical year. Thus the months of the Islamic calendar systematically shift with respect to the months of the Gregorian calendar. The third type of calendar, the lunisolar calendar, has a sequence of months based on the lunar phase cycle; but every few years a whole month is intercalated to bring the calendar back in phase with the tropical year. The Hebrew and Chinese calendars are examples of this type of calendar.
Because calendars are created to serve societal needs, the question of a calendar’s accuracy is usually misleading or misguided. A calendar that is based on a fixed set of rules is accurate if the rules are consistently applied. For calendars that attempt to replicate astronomical cycles, one can ask how accurately the cycles are replicated. However, astronomical cycles are not absolutely constant, and they are not known exactly. In the long term, only a purely observational calendar maintains synchrony with astronomical phenomena. However, an observational calendar exhibits short-term uncertainty, because the natural phenomena are complex and the observations are subject to error.

What are Equinoxes and Solstices?

Equinoxes and solstices are frequently used as anchor points for calendars. For people in the northern hemisphere:
  • Winter solstice is the time in December when the sun reaches its southernmost latitude. At this time we have the shortest day. The date is near 21 December.
  • Summer solstice is the time in June when the sun reaches its northernmost latitude. At this time we have the longest day. The date is near 21 June.
  • Vernal equinox is the time in March when the sun passes the equator moving from the southern to the northern hemisphere. Day and night have approximately the same length. The date is near 20 March.
  • Autumnal equinox is the time in September when the sun passes the equator moving from the northern to the southern hemisphere. Day and night have approximately the same length. The date is near 22 September.
For people in the southern hemisphere, winter solstice occurs in June, vernal equinox in September, etc.
The astronomical "tropical year" is frequently defined as the time between, say, two vernal equinoxes, but this is not actually true. Currently the time between two vernal equinoxes is slightly greater than the tropical year. The reason is that the earth’s position in its orbit at the time of solstices and equinoxes shifts slightly each year (taking approximately 21,000 years to move all the way around the orbit). This, combined with the fact that the earth’s orbit is not completely circular, causes the equinoxes and solstices to shift with respect to each other.
The astronomer’s mean tropical year is really a somewhat artificial average of the period between the time when the sun is in any given position in the sky with respect to the equinoxes and the next time the sun is in the same position.

Did the church study astronomy?

Yes, it did.
Although the Roman Catholic Church once waged a long and bitter war on science and astronomy (particularly condemning Galileo), in general, they were quite involved in astronomy. The church gave more financial and social support to the study of astronomy for over six centuries, from the recovery of ancient learning during the late Middle Ages into the Enlightenment, than any other, and probably, all other, institutions. The church was not necessarily seeking knowledge for knowledge’s sake, a traditional aim of pure science. Rather, like many patrons, it wanted something practical in return for its investments: mainly the improvement of the calendar so church officials could more accurately establish the date of Easter.
When to celebrate the feast of Christ’s resurrection had become a bureaucratic crisis in the church. Traditionally, Easter fell on the Sunday after the first full moon of spring. But by the 12th century, the usual ways to predict that date had gone awry. To set a date for Easter Sunday years in advance, and thus reinforce the church’s power and unity, popes and ecclesiastical officials had for centuries relied on astronomers, who pondered over old manuscripts and devised instruments that set them at the forefront of the scientific revolution.
In its scientific zeal, the church adapted cathedrals across Europe, and a tower at the Vatican itself, so their darkened vaults could serve as solar observatories. Beams of sunlight that fell past religious art and marble columns not only inspired the faithful but provided astronomers with information about the Sun, the Earth and their celestial relationship. Among other things, solar images projected on cathedral floors disclosed the passage of dark spots across the Sun’s face, a blemish in the heavens, which theologians once thought to be without flaw. Over the centuries, observatories were built in cathedrals and churches throughout Europe, including those in Rome, Paris, Milan, Florence, Bologna, Palermo, Brussels and Antwerp.

Didn’t the church condemn Galileo?

Yes. The traditional view of the church’s hostility toward science grew out of its famous feud with Galileo, condemned to house arrest in 1632 for astronomical heresy.
Since antiquity, astronomers had put Earth at the center of planetary motions, a view the church had embraced. But Galileo, using the new telescope, became convinced that the planets in fact moved around the Sun, a view Nicholas Copernicus, a Polish astronomer, had championed.
The censure of Galileo, at age 70, hurt the image of the church for centuries. In 1992, 359 years later, Pope John Paul II finally acknowledged that the church had erred in condemning the scientific giant. Although some scholars claim that Rome’s handling of Galileo made Copernican astronomy a forbidden topic among faithful Catholics for two centuries, in fact, Rome’s support of astronomy was considerable. The church tended to regard all the systems of the mathematical astronomy as fictions. That interpretation gave Catholic writers scope to develop mathematical and observational astronomy almost as they pleased, despite the tough wording of the condemnation of Galileo.

How did the observatories work?

Typically, the building, dark inside, needed only a small hole in the roof to allow a beam of sunlight to strike the floor below, producing a clear image of the solar disk. In effect, the church had been turned into a pinhole camera, in which light passes through a small hole into a darkened interior, forming an image on the opposite side.
On each sunny day, the solar image would sweep across the church floor and, exactly at noon, cross a long metal rod that was the observatory’s most important and precise part. The noon crossings over the course of a year would reach the line’s extremities – which usually marked the summer and winter solstices, when the Sun is farthest north and south of the Equator. The circuit, among other things, could be used to measure the year’s duration with great precision.
The path on the floor was known as a meridian line, like the north-south meridians of geographers. The rod, in keeping with its setting and duties, was often surrounded by rich tile inlays and zodiacal motifs. The instruments lost much of their astronomical value around the middle of the 18th century as telescopes began to exceed them in power. But the observatories still played a significant role because the solar timepieces were often used to correct errors in mechanical clocks and even to set time for railroads.
One of the observatories also impressed Charles Dickens, who in his book Pictures from Italy wrote that he found little to like in Bologna except "the Church of San Petronio, where the sunbeams mark the time among the kneeling people." Today, the surviving cathedral solar instruments are lovely anachronisms that baffle most visitors, who are usually unaware of their original use or historical importance. In the book, The Sun in the Church, author Dr. Heilbron, describes his astonishment with seeing the old instruments in Bologna, Italy, at the Basilica of San Petronio. "The church itself was beautiful, somber," Dr. Heilbron recalled. "When the sun crawled across that floor, there was nothing else. That’s what you had to look at. It was intense."
In the great Basilica of San Petronio, a solar observatory was erected in 1576 by Egnatio Danti, a mathematician and Dominican friar who worked for Cosimo I dei Medici, the Grand Duke of Tuscany, and who advised Pope Gregory on calendar reform. The church observatory produced data long before the telescope existed. By 1582, the Gregorian calendar had been established, creating the modern year of 365 days and an occasional leap year of 366 days. Danti was rewarded with a commission to build a solar observatory in the Vatican itself within the Torre dei Venti, or Tower of the Winds. The golden age of the cathedral observatories came later, between 1650 and 1750, and helped to disprove the astronomical dogma that the church had defended with such militancy in the case of Galileo.
Kepler's Model of the Universe
Kepler’s Model of the Universe
Another model of the heavens is that we’ve seen before is Kepler’s nested Platonic solids, and another is the dome. In The Dome of Heaven, Karl Lehmann, who writes, "One of the most fundamental artistic expressions of Christian thought and emotion is the vision of heaven depicted in painting or mosaic on domes..."

How did Cassini prove Kepler was right?

Among the best known of the rebel observers was Giovanni Cassini, an Italian astronomer who gained fame for discovering moons of Saturn and the gaps in its rings that still bear his name. Around 1655, Cassini persuaded the builders of the Basilica of San Petronio that they should include a major upgrade of Danti’s old meridian line, making it larger and far more accurate, its entry hole for daylight moved up to be some 90 feet high, atop a lofty vault. "Most illustrious nobles of Bologna," Cassini boasted in a flier drawn up for the new observatory, "the kingdom of astronomy is now yours." The exaggeration turned out to have some merit as Cassini used the observatory to investigate the "orbit" of the Sun, quietly suggesting that it actually stood still while the Earth moved. Cassini decided to use his observations to try to confirm the theories of Johannes Kepler, the German astronomer who had proposed in 1609 that the planets moved in elliptical orbits not the circles that Copernicus had envisioned.
If true, that meant the Earth over the course of a year would pull slightly closer and farther away from the Sun. At least in theory, Cassini’s observatory could test Kepler’s idea, since the Sun’s projected disk on the cathedral floor would shrink slightly as the distance grew and would expand as the gap lessened. Such an experiment could also address whether there was any merit to the ancient system of Ptolemy, some interpretations of which had the Earth moving around the Sun in an eccentric circular orbit. Ptolemy’s Sun at its closest approach moved closer to the Earth than Kepler’s Sun did, in theory making the expected solar image larger and the correctness of the rival theories easy to distinguish.
For the experiment to succeed, Cassini could tolerate measurement errors no greater than 0.3 inches in the Sun’s projected face, which ranged from 5 to 33 inches wide, depending on the time of year. No telescope of the day could achieve that precision. The experiment was run around 1655, and after much trial and error, succeeded. Cassini and his Jesuit allies confirmed Kepler’s version of the Copernican theory.
Between 1655 and 1736, astronomers used the solar observatory at San Petronio to make 4,500 observations, aiding substantially the tide of scientific advance.
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