Ensuring of quality of NASA JPL's ephemeris I was checking them for deriving by MICE (SPICE for MatLab) of "the length of mean solar day" - LOD
My method was :
- so as to level influence of eccentricity of Earth, the beginnings of periods had set on to aphelions or perihelions
- for ancient epoch I'm using IAU Earth frame, for 1962-2007 AC epoch ITRF93 frame.
- I was using DE422 ephemeris and once DE408 for comparing
- Observer place - Cairo settled in calculation by using created by pinpoint.exe my own *.bsp file.
- I was seeking for epochs of aphelions (perihelions) of Earth for certain period
- for some test additionally seeking for nearest from aphelions (perihelions) azimuth of sun =0° (midnight) or 180° (noon)
- then add 365 days each of 86400 atomic seconds for estimation of the end the period, and seek at this border +- 0.48 day the same azimuth of Sun, or azimuth = 0° or 180°
- for some test additionally seeking for nearest azimuth of sun =0° (midnight) or 180° (noon) for 356-th solar day's border
- divide the period by 365 and have got the "mean solar day from aphelion noon" or others
I was expecting that LOD will be increasing, but have get some amazing shapes graphs (XLS data sheet attached ) ... where often the LOD is decreasing ...
1. Why LOD is decreasing, when it is on contrary increasing?
so amazing figures dependent from different times of the day from aphelions :
The mean LOD of a period of 365 solar days beginning from vernal equinoxes. So level dispersion ...
2. Why spread diapason of MEAN LOD and graph shapes are the same for spread of MEAN LOD and spread of difference of MEAN LODs for different observers?
3. What had happened in ~1635 BC (take a look at graph)
5. Why graph have such a shapes depended to moments chosen for period (aphelion, noon, midnight)? See XLS attached.
6. How is right to imitate deriving of LOD from ephemeris like as if from real observations?
... and so on... http://bible-exodus.narod.ru/tmp/LOD_derived_from_JPL_ephemeris_ITRF93.xls
Excuse my bad English ...
Best regards, Poltavsky Sasha