Dear Brent, Thank you for your follow-up...
> While I am trying to digest all of that I > have a new question. > > Do the ancient solar calendars like the > Incas still work? > > Do their rocks still show where the > solstices will occur now? I am not an expert in this area and others may supply more detailed comments. I can see no reason why such instruments cannot, at least approximately, show when the solstices occur but there are practical difficulties... Around the solstices, the declination changes ever so slowly, so pin-pointing the precise moment of a solstice is hard even with modern instrumentation. Also, the obliquity of the ecliptic keeps changing and this affects the declination at the solstices and hence the direction of the sun at sunrise and sunset at those times. > Your explanation below seems to indicate > that their calendars would get progressively > worse in predicting the day of solstices. Well, their instruments (if you can call them that) will give progressively worse indications of the day on which the solstices fall but that isn't, quite, the same thing as commenting on the associated calendar. The Gregorian calendar suffers from drift but that has nothing to do with the change in the position of sunrise at the solstices! > On a side thought, the problem seems to be > that we are using the time for the earth to > spin around (a day) to measure the time it > takes the earth to go around the sun (a year). > These are two different events and it doesn't > make sense to use one to measure the other. Well, it makes some kind of sense. We need to know how many days there are in a year for all kinds of reasons. The snag is that the ratio year:day is not a constant. > A day is a day and a year is a year, we > shouldn't mix the two as it makes for a > very messy situation. Alas, the closer you look into the behaviour of the Earth-Sun system the messier it gets. The variability of the year:day ratio is just one of many messes. > Forget the Popes calendar... I do my best :-) > ...can't I make a solar calendar that depicts > a true solar year? Well, only up to a point. > It would mark the two solstices, the time between > those two points is half a solar year. That is your first mistake. The time between the winter solstice and the summer solstice is not the same as the time between the summer solstice and the winter solstice. You instantly fall into the problem of having two different lengths of half-year. > Half way in between those are the two equinoxes > which would mark 1/4 of a year and we could keep > halving the differences to get 1/8, 1/16, 1/32, > 1/64 of a year etc... Alas, your four quarters are all of different length and your eight eighths are all of different length and so on. This may not matter but you would have to accept that your sub-divisions are not the same length. > So we don't try to define a year in earth days > but just split up a true year into equal parts. Yes. I can buy that scheme but your parts are not equal alas! Just try counting the days from the March equinox this year to the September equinox and then count the number of days from the September equinox to the March equinox next year. You will find over a week's difference. To be sure, you are not wanting to use the day as a unit of time but you are wanting to use the half-year as a sub-unit and your half-years have different lengths. > And this solar calendar would need no leap > year and would always be correct. There is something in what you say but I am not sure that the word calendar is appropriate. To me, a calendar really is about relating days to years. Pope Gregory's scheme is one way to do this. Your proposal, which does its best to ignore the concept of a day, is something altogether different. > Maybe :) Maybe indeed! All the best Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
