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<TITLE>Re : Uncertain sequences (was Re: TR : Re : The OEIS will be on holiday for the rest of the year!)</TITLE>
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<FONT COLOR="#FF0000">>> Alexandre:<BR>
>>And why are at least no less interessant sequences than supra not accepted?<BR>
>>(ex: 1903, 2303, 2307, 2311, 2315... "Exceptional years of 23rd december's<BR>
>>winter solstice since the beginning of the Gregorian Calendar in 1582" is no<BR>
>>less interessant than a "word" sequence).<BR>
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Me <BR>
As I said earlyer, actually I didn't submit it because of the moratorium in december. But I will -Thanx Neil<BR>
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><FONT COLOR="#008000">>Jaap:<BR>
>>Calculating solstices (and other phenomena) in the far future<BR>
>>is uncertain because of the unpredictable earth rotation.<BR>
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Yes uncertain but in a very far future! Although such sequences are infinite by definition (actually not!: max n = more or less 5.10^9, when the Sun will blast in a red giant star and "eat" the Earth), we know their relevancy is limited, say, to a few centuries from now on... So, such a sequence could be "tackled" from another point of vue: not the *values* a(n) (i.e. "are they correct for all n's"), but *n*: the domain of validity of such sequences, domain we have to define. <BR>
So...:<BR>
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<FONT COLOR="#008000">>>Jaap<BR>
>>What is the DELTA T (.</FONT>..)<FONT COLOR="#008000"> DELTA T now is<BR>
>approximately 65 s, but what will it be in the year 3000?<BR>
>There is another uncertain factor in the calculations and that is<BR>
>the planetary model. Some calculations use the VSOP 87 model and<BR>
>others depend on the JPL ephemerides from NASA.<BR>
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Right, the definition should be more precise. These dates are published by IMCCE - Institut de Mécanique Céleste et de Calcul des Éphémerides, but the informations (DELTA T etc) are not explicite there:<BR>
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<a href="http://www.imcce.fr/page.php?nav=en/ephemerides/astronomie/saisons/presentation_saisons.php">http://www.imcce.fr/page.php?nav=en/ephemerides/astronomie/saisons/presentation_saisons.php</a><BR>
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If you have easy accessible information and would like to submit...<BR>
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<FONT COLOR="#0F9EFF">> Brendan<BR>
> There is in fact an algorithm<BR>
> for computing it correctly - wait for each event to happen. This<BR>
> is a rather slow algorithm, but an algorithm nevertheless.<BR>
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</FONT>Like for the sequence, I don't remember the number, which goes so:<BR>
1,2,3,4,5,6,7,8.....29,30,31,31,31,31,31...: "the years of the life of Mr Smith, f(t)".<BR>
It's not only a joke, but an exemple of sequences defined in the past, which is the case for this astronomical sequences. (Smith is defined in the future also but it's trivial)<BR>
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<FONT COLOR="#0A28A5">Jaap<BR>
There is one sure entry: 1903. But not in Russia where the Gregorian calendar<BR>
was introduced in 1918!<BR>
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Correct. But it doesn't matter what calendar is in use here or there since the definition <gregorian calendar> implies peoples and countries which are using it.<BR>
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Thanx for documented questioning and interest. I'll let you know when I'll complete the job (at least my part of) or need help.<BR>
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Alexandre<BR>
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