# RE: LeapYears of Iranian Calendar

```On Fri, 21 May 2004, Ordak D. Coward wrote:

> I guess the best thing to do:
>
> - is get an archive of the last 50 years of official times of
> vernal equinox, or saal tahveel, and compute the length of
> year for each year. Fit them with linear or quadratic curves.
> Look at  Birashk's method and see how much Birashk's length
> of year differs from official length of year. Also, look at
> the real variation of length of years, compute the calendar
> for the next 1000 years using both Birashk and the curves.
> Decide if using the curves will result in less error.```
```
Good idea, if we can collect the list of Tahveel moments for the passed
years, I think I can easily prepare the curves with my implemented
calendar. It uses .NET DateTime objects with a presicion of 100
nanosecond (namely a tick). It also supports dates up to year 9378 A.P
(Anno Persico). But before that I have to manipulate a line of code to
work with Birashk's leap years.

>
> Here is an attempt to guesstimate when the official calendar
> starts to diverge from Birashk's. A rough look at the last
> few years variation of length of years show a variation of up
> to 5 minutes.  So, each 144 years or so (24hours / 10
> minutes) , we have a year whose VE is +/- 5 minutes of noon.
> Hence, as long as we use a constant for the length of year,
> it is very likely to see discrepancies once every 144 years.
> However, this WILL happen as early as 1404. That is, if my
> calculations are correct Birashk's method gives year 1404 as
> a leap year, but I get 1403 as a leap year. (I am using some
> acceptable length of years). That is, the VE of year 1404
> should happen around 12:30pm which if it considered
> afternoon, it shall be Esfand 30th of 1403. THIS IS IMPORTANT
> AND SHOULD BE DEALT WITH. No amount of observational errors
> can compensate this.
>
> Considering the computational power available today, it is a
> shame if we stick to a method using constant length of year
> which were only appropriate for pre-computer era.
>

I guess you're right. Since "Showraaye Taghvim" announces their own
calculation of the VE every year, their estimation may disagree with
that of Birashk in the next few decades. So we should choose the
algorithm that matches the real world as close as possible.

> --
> ODC

Omid

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