[time-nuts] GPS disciplined Mars clock
holrum at hotmail.com
Sun Jul 10 14:25:45 EDT 2016
I found some test data and tried those values with my code. They agree to within a millisecond... and that difference is caused by my JD to Gregorian routine that adds a millisecond to the JD input to compensate for possible tiny double precision math errors... All of Lady Heather's times are calculated in Julian to with fractional seconds, but the time displays are all truncated to seconds (since the screen is updated on one second intervals synced to the GPS receiver time message). Without the millisecond fudge, those math errors can occasionally cause what appears to be a duplicated/skipped time stamp.
I looked into adding BJD support but that requires some hairy calculations that depend upon externally supplied ephemeris, etc data... some of the equations can have thousands of coefficients. Also, BJD usage is generally applicable only when observing things way out in space. Most BJD routines barf when the distance is within the solar system. I'm now looking at adding HJD support... Heliocentric Julian Date, where instead of the solar system barycenter, the reference location is the center of the sun. That can be done without the need of external data. The time difference between BJD and HJD is around +/- the light travel time across the sun radius (the solar system barycenter generally stays within the sun). Since Lady Heather is not observing some external event, the HJD would basically be JD adjusted for the light travel time between you and the center of the sun... cool, but not all that useful (just like many of the things that Lady Heather can do).
> Source code to do the conversion also on above site. You should just use
their code as it is known correct .
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