[EMAIL PROTECTED] (Danny Mayer) writes: >Unruh wrote: >> [EMAIL PROTECTED] (Danny Mayer) writes: >> >>> Unruh wrote: >>>> "David L. Mills" <[EMAIL PROTECTED]> writes: >>>> >>>>> Brian, >>>>> The longest delay NTP response was from the Moon, as simulated at JPL. >>>>> Next step is the Mars orbiters and then the rovers. JPL discovered the >>>>> max distance threshold had to be increased to handle the Moon delay. >>>> Thats only a few sec. >>>> And it is symmetrical. Could probably still get usec resolution. >> >>> Of course it's not symmetrical. You of all people should know better >>> than that. >> >> The speed of light differs in different directions? >> And if the response is fast, the distance has not changed much either >> (In a msec the moon moves about a meter, which is 3nsec, way below any >> computer resultion)and that is amost all perp to the earth.Ie, the >> difference in distance during the response time of the remote computer is >> negligible. If you aim for the moon when the moon is just setting and you >> are on the equator, the difference in path lengths is about 5usec, again, a >> completely negligible amount. >> >> Now of course the synchronization will not proper time on the moon, but the >> sync of the earth clock.
>And neither the moon or other is moving along their geodesic? The moon is, but that is irrelevant if the moon is the server.(Ie, if the earth is using ntp to query the moon to see how far off the moon's clock is). If the moon is the client, (Ie trying to sync to the earth) then the moon's motion is almost all perpendicular to the earth observer. ( It is only the component of the moon's motion that ncreases the distance from the earth that is important, which is onl;y 1/60 of the moon's proper motion. ) That makes a difference in travel time only when the moon is rising or setting and even then it is only about 12m/s, which over the 5 sec travel time is only about .2usec, a trivial amount, lost in all other noises. It also depends on what synchronization frame you want to use (relativistically). But all of these corrections are at the usec level. >Danny _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
