# Thread: Solar Cycle - slight change?

1. ## Solar Cycle - slight change?

The tropical year, on which our solar Gregorian calendar is based, is 365.2422 days. Was it always so? I am wondering if in a previous era (about 3000 years back) it could have been 365.14 days.

No, Im not doing a "Velikovski" who suggested a 360-day. Such an idea was obviously too big a variation. My suggestion would only be 2 hrs, 27 minutes per year. Would that be feasible? Any thoughts?

Cyberseeker

2. Originally Posted by Cyberseeker
The tropical year, on which our solar Gregorian calendar is based, is 365.2422 days. Was it always so? I am wondering if in a previous era (about 3000 years back) it could have been 365.14 days.
From what I see by searching, it's going the other way.
Wiki has a chart showing 2000 vs 0 where the values back then were longer. It also gives a formula for computing it:
365.2421896698 − 6.15359×10^−6T − 7.29×10^−10T2 + 2.64×10^−10T3where T is in Julian centuries of 36,525 days measured from noon January 1, 2000 TT
Another site I found, has a simpler (rough approximation) of that formula:
difference (days) = −0.000 000 061 62×a days (a in Julian years from 2000), or about 5 ms/year, which means that 2000 years ago the tropical year was 10 seconds longer.
Knowledge is just a google away.

3. From looking at those sites, I'm intrigued to notice that although the mean year varies extremely slowly (by seconds over millennia), the individual variation from year to year (apparently due to nutation, perturbation from the other planets, and so forth) can be a couple minutes from year to year. I'm surprised to see that it can be that large.

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No, Im not doing a "Velikovski" who suggested a 360-day. Such an idea was obviously too big a variation. My suggestion would only be 2 hrs, 27 minutes per year. Would that be feasible? Any thoughts?

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pakistan

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