[tz] Sol 5000 for Opportunity

[Paul Eggert]

Tim Parenti wrote:
> Today, 16 February 2018, at 01:26:20.092 UTC, it is 01:01:06 Coordinated
> Mars Time on Mars Sol Date 51235

What's the source for these timestamps? It's an Earth reference frame, surely?

Because of relativistic effects, if an observer on Earth sees that Mars's 51235 
01:01:06.000 CMT timestamp corresponds to Earth's 2018-02-16 01:26:20.092 UTC 
timestamp, then I guess that an observer on Mars should see that the same CMT 
timestamp corresponds to a slightly-different UTC timestamp, even assuming both 
observers have error-free measurements, and that the difference will be 
observable with millisecond-precision timestamps. This is due to both the 
relative velocity of the Earth and Mars and to gravitational-field effects. For 
millisecond/year precision Pan and Xie write that you need to figure in not only 
the gravitational effects of the Earth, Mars, and the Sun, but also those of 
Jupiter, Saturn, the Moon, and Venus (!). See their analytic model of 
timekeeping for a Yinghuo-1-like mission in:

Pan J-Y, Xie Y. Relativistic algorithm for time transfer in Mars missions under 
IAU resolutions: an analytic approach. RAA. 2015. 15(2):281-92. 
https://dx.doi.org/10.1088/1674-4527/15/2/011 
http://www.raa-journal.org/raa/index.php/raa/article/download/1875/1791

The whole idea of time transfer between Mars and Earth brings into stark relief 
what an easy job it is to track civil timekeeping on Earth, compared to how it 
would be elsewhere. And Mars is an easy case. Someone should alert Elon Musk.