View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0002778 | SkyChart | 1-Software | public | 24-11-26 13:06 | 24-12-09 10:41 |
| Reporter | pmaigne | Assigned To | |||
| Priority | urgent | Severity | major | Reproducibility | always |
| Status | resolved | Resolution | no change required | ||
| Platform | PC | OS | Windows | OS Version | 10 64bit |
| Product Version | 4.2 | ||||
| Summary | 0002778: BCE event date are late compared to similar CE event date | ||||
| Description | The BCE dates are late compared to similar event in CE date based on the same calendar scheme used by Skychart. It is presumed that it is due to the Earth's rotation model which is not based on corresponding data for BCE. The more we go in the past the more the difference increase. For example, by comparing the winter solstice date in CE (December 21) and in 4000 BCE, the BCE dates generated are about 30 days late, in 3038 and 3019 by 24 days, in 1000 by 8 days, in 500 by 5 days, in 100 by 2 days. In BCE the winter solstice is visually found by selecting the date having the sun lowest altitude above the horizon at mid-day. Could you confirm or provide an explanation about such differences. Best regards | ||||
| Steps To Reproduce | BCE 4000 January 19 BCE 3038 January 13 BCE 1000 December 29 BCE 500 December 26 | ||||
| Tags | No tags attached. | ||||
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This is simply because CdC use the Julian calendar for every date before 1582. The difference in the length of the year 365.25 - 365.2422 produce an offset of 7.8 days every 1000 years. This offset is the reason Gregory reform the calendar in 1582. The advantage of using the Julian calendar is it directly give the date in use between 46 BCE and 1582, and for previous date it make relatively easy to convert to the calendar effectively in use in the area of interest. |
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One more point, there is a setting in CdC to modify the date the calendar change from Julian to Gregorian. This was intended for non catholic countries that not change in 1582 but later. You can access the setting by using the button "More options" in the Time setup. It was not intended for this use but I just test it work if you set a negative year here. Set it to -10000 for example and it show the date you expect for the event you mention, and spring equinox on BCE 4000 March 21. But be careful this date meant nothing and will be wrong if you try to match a medieval eclipse observation for example. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 24-11-26 13:06 | pmaigne | New Issue | |
| 24-11-26 14:04 | Patrick Chevalley | Note Added: 0009199 | |
| 24-11-26 14:21 | Patrick Chevalley | Note Added: 0009200 | |
| 24-12-09 10:41 | Patrick Chevalley | Status | new => resolved |
| 24-12-09 10:41 | Patrick Chevalley | Resolution | open => no change required |
