Do we even really know the exact days anymore? For all we know the true Sabbath could be a Wednesday or Thursday.
I happen to believe that there are some things that are part of the natural order of creation long before the Law of Moses...male headship, tithes (Abraham paid them), a sabbath rest, a blood sacrifice to please God (Abel vs Cain). So I do believe in honoring a day a week to devote to the Lord, the same way I tithe, and submit to hub/elders and put my trust in the blood sacrifice to please God. But I've seen enough wrangling about calendars and dates out there by the messianic believer types to think that we can't know anymore which day is the Sabbath anyway. Perhaps that is good; we can keep our focus on the Lord! You want to take Wednesday off, well, go right ahead!
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Astronomy Answers: Modern Calendars
The Gregorian calendar is a modified version of the Julian calendar. Modification was necessary because the average length of the Julian calendar year, 365 1/4 day, was about 11 minutes too long compared to the March equinox year so that the vernal equinox (the beginning of spring in the northern hemisphere) moved backwards through the calendar year by about one day per 131 years. When the Julian calendar was introduced, in −44, the vernal equinox fell around 25 March. At the time of the Council of Nicaea in 325 the vernal equinox had shifted to 21 March, and the rules for determining the date of Easter were based on that date. Around 1500 the vernal equinox had shifted further back to about 11 March. For this and other reasons, Pope Gregory XIII proclaimed the new calendar rules that define what we now call the Gregorian calendar.
To make the calendar year follow the return of the vernal equinox more closely, the last two leap year rules listed above were promulgated. To get the vernal equinox back to 21 March, the Pope decreed that the day following 4 October 1582 be called 15 October 1582,
thereby skipping 10 days of the calendar.
The Gregorian calendar reform was adopted quickly in the Catholic regions of the world (of which the Pope was the religious leader), but there was a lot of resistance to the reform in Protestant areas. Many Protestant areas started using the Gregorian calendar around 1700. Great Britain and its possessions followed in 1752, and Russia in 1918.
It is clear that the gradual acceptance of the Gregorian calendar causes no end of problems in accurately dating dates from the period. A date in 1612, for example, is probably on the Gregorian calendar if it occurs on a letter sent from a Catholic country, but probably on the Julian calendar if it is on a letter sent from a Protestant country.
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Also, the Jews had to figure out when to add a 13th month to the calendar according to when the barley ripened. That practice stopped a long time ago. Even if we tried to go back to the OT calendar we would not ever know how to figure the dates properly unless we had a agricultural record of the barley ripening every spring.