Today, 16 February 2018, at 01:26:20.092 UTC, it is 01:01:06 Coordinated Mars Time on Mars Sol Date 51235, which corresponds to midnight HLST (hybrid local solar time) at the beginning of mission sol 5000 for the Opportunity (MER-B) rover at its mission reference longitude. The sol will last, of course, for 24 hours 39 minutes 35.244 seconds, ending on 17 February 2018 at 02:05:55.336 UTC. Curiosity will observe its mission sol 2000 next month, reckoned in mean solar time at its landing site, from 2018-03-22 13:24:49.020 UTC to 2018-03-23 14:04:24.264 UTC. -- Tim Parenti
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.
On Sat 2018-02-17T18:46:11-0800 Paul Eggert hath writ:
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.
He knows, he's launching it on the next Falcon Heavy https://forum.nasaspaceflight.com/index.php?topic=30544.0 https://www.nasa.gov/feature/goddard/2018/nasa-tests-atomic-clock-for-deep-s... https://www.jpl.nasa.gov/missions/deep-space-atomic-clock-dsac/ -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
On Sat, Feb 17, 2018 at 9:46 PM, Paul Eggert <eggert@cs.ucla.edu> wrote:
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?
The short answer is that so far, it effectively is. Mars spacecraft keep (so far) an effective Earth time.Their clocks (so far) typically aren't that good, and so they are just treated as if they were on TAI or even UTC and adjusted from time to time to keep close to Earth time. Mars Coordinated Time (or MTC) is the Mars Mean Solar Time (the Mars equivalent of UT1) for the Mars reference longitude (crater Airy-0). However, I believe that all of the lander/rover missions to date use actually the mean solar time for their latitude and longitude (roughly, UT0 + a longitude correction) in setting their sols and the local solar time. No spacecraft clock is AFAIK set to run at MTC. The Martian local solar time undergoes fairly large variations over a Martian year, much as the local solar time does on Earth, but more so, due to the larger orbital eccentricity. The wikipedia article describes these and provides a formula for getting MST from terrestrial time (TT = TAI + 32.184 seconds). I helped to determine the mean Mars length of day (LOD) and what little is known about its variations from Viking and Pathfinder data. There is a fairly large seasonal variation of Mars LOD (due to the seasonal transfer of CO2 to and from the poles) but little is known about any long period changes in Martian LOD, and thus it is not known whether leap seconds would be needed to keep Mars atomic time (once that is set up) and Mars mean solar time aligned. The Wikipedia article does not discuss the relativistic differences between time on the Earth and time on Mars, but these are significant; Mars is both traveling slower on its orbit and further out in the Sun's gravitational potential. Atomic time on Mars would run faster than AT on Earth by about 5.1 x 10^-9, or ~0.16 seconds per year, on average, and there are seasonal and other variations. This is taken into account in great detail in the Martian ephemeris work, but so far as far as I know the people setting the spacecraft clocks ignore it. The long awaited arrival of the first Deep Space Atomic Clock into Mars orbit will change all of this. That will not be adjusted in rate and thus would run fast by 3.4 parts per billion (on average) compared to its cousins back here on or near Earth, or roughly 7 orders of magnitude above its hoped-for sensitivity level. How (or even whether) future Mars colonists will align their time with the Earth's remains to be seen. Regards Marshall
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.
On Sat, Feb 17, 2018 at 11:48 PM, Marshall Eubanks < marshall.eubanks@gmail.com> wrote:
On Sat, Feb 17, 2018 at 9:46 PM, Paul Eggert <eggert@cs.ucla.edu> wrote:
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?
The short answer is that so far, it effectively is.
Mars spacecraft keep (so far) an effective Earth time.Their clocks (so far) typically aren't that good, and so they are just treated as if they were on TAI or even UTC and adjusted from time to time to keep close to Earth time.
Mars Coordinated Time (or MTC) is the Mars Mean Solar Time (the Mars equivalent of UT1) for the Mars reference longitude (crater Airy-0). However, I believe that all of the lander/rover missions to date use actually the mean solar time for their latitude and longitude (roughly, UT0 + a longitude correction) in setting their sols and the local solar time. No spacecraft clock is AFAIK set to run at MTC.
The Martian local solar time undergoes fairly large variations over a Martian year, much as the local solar time does on Earth, but more so, due to the larger orbital eccentricity. The wikipedia article describes these and provides a formula for getting MST from terrestrial time (TT = TAI + 32.184 seconds).
I helped to determine the mean Mars length of day (LOD) and what little is known about its variations from Viking and Pathfinder data. There is a fairly large seasonal variation of Mars LOD (due to the seasonal transfer of CO2 to and from the poles) but little is known about any long period changes in Martian LOD, and thus it is not known whether leap seconds would be needed to keep Mars atomic time (once that is set up) and Mars mean solar time aligned.
The Wikipedia article does not discuss the relativistic differences between time on the Earth and time on Mars, but these are significant; Mars is both traveling slower on its orbit and further out in the Sun's gravitational potential. Atomic time on Mars would run faster than AT on Earth by about 5.1 x 10^-9, or ~0.16 seconds per year, on average, and there are seasonal and other variations. This is taken into account in great detail in the Martian ephemeris work, but so far as far as I know the people setting the spacecraft clocks ignore it.
The long awaited arrival of the first Deep Space Atomic Clock into Mars orbit will change all of this. That will not be adjusted in rate and thus would run fast by 3.4
argh! That's 5.1 not 3.4, of course. I recommend this paper as an introduction to the theory here : http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1986AJ.....91..650H&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf parts per billion (on average) compared to its cousins back here on or near
Earth, or roughly 7 orders of magnitude above its hoped-for sensitivity level.
How (or even whether) future Mars colonists will align their time with the Earth's remains to be seen.
Regards Marshall
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.
On 2018-02-17 21:48, Marshall Eubanks wrote:
On Sat, Feb 17, 2018 at 9:46 PM, Paul Eggert wrote: 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?
The short answer is that so far, it effectively is.> Mars spacecraft keep (so far) an effective Earth time. Their clocks (so far) typically aren't that good, and so they are just treated as if they were on TAI or even UTC and adjusted from time to time to keep close to Earth time.> Mars Coordinated Time (or MTC) is the Mars Mean Solar Time (the Mars equivalent of UT1) for the Mars reference longitude (crater Airy-0). However, I believe that all of the lander/rover missions to date use actually the mean solar time for their latitude and longitude (roughly, UT0 + a longitude correction) in setting their sols and the local solar time. No spacecraft clock is AFAIK set to run at MTC. JPL have defined time zones based on Airy Mean Time: see under Local and "Zonal" Times in:
https://www.giss.nasa.gov/tools/mars24/help/notes.html based on: https://doi.org/10.1016/j.icarus.2013.11.015
The Martian local solar time undergoes fairly large variations over a Martian year, much as the local solar time does on Earth, but more so, due to the larger orbital eccentricity. The wikipedia article describes these and provides a formula for getting MST from terrestrial time (TT = TAI + 32.184 seconds).> I helped to determine the mean Mars length of day (LOD) and what little is known about its variations from Viking and Pathfinder data. There is a fairly large seasonal variation of Mars LOD (due to the seasonal transfer of CO2 to and from the poles) but little is known about any long period changes in Martian LOD, and thus it is not known whether leap seconds would be needed to keep Mars atomic time (once that is set up) and Mars mean solar time aligned.
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 Wikipedia article does not discuss the relativistic differences between time on the Earth and time on Mars, but these are significant; Mars is both traveling slower on its orbit and further out in the Sun's gravitational potential. Atomic time on Mars would run faster than AT on Earth by about 5.1 x 10^-9, or ~0.16 seconds per year, on average, and there are seasonal and other variations. This is taken into account in great detail in the Martian ephemeris work, but so far as far as I know the people setting the spacecraft clocks ignore it. The long awaited arrival of the first Deep Space Atomic Clock into Mars orbit will change all of this. That will not be adjusted in rate and thus would run fast by 3.4 parts per billion (on average) compared to its cousins back here on or near Earth, or roughly 7 orders of magnitude above its hoped-for sensitivity level. JPL needs to set up an [I]MRS to coordinate TAM, MTC(Airy), model and measure dMT. TAI, UTC, UTn may need renamed to TAT, TTC, TTn, and work started on newer solar system referenced realizations of TAS, STC, STn. Pretty presumptuous of the IAU to use Universal: they /should/ know better. At least the Brits only claim GMT is accurate at Greenwich: after the adoption of Greenwich (approx.) as the International Meridian at the eponymous Conference, perhaps they should have kept the pattern and called it IMT, although the French may have preferred TIM (old UK phone # for talking clock), TMI, or compromised on MIT.
How (or even whether) future Mars colonists will align their time with the Earth's remains to be seen.
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. He'd claim to use Terra Time, but we'd all know it really meant Tesla Time ;^>
-- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
On Sun 2018-02-18T00:08:25-0700 Brian Inglis hath writ:
Pretty presumptuous of the IAU to use Universal: they /should/ know better.
Alas, Universal Time of 1928 is a subdivision of the already approved Universal Day, and that derives from the Victorian-era knowledge of astronomy and speech patterns of the 1884 International Meridian Conference. Of regrettable things left over from time-keeping history, that is not the worst, and the Germans did explicitly avoid it by choosing Weltzeit as their term. If Mars denizens decide to choose a single legal time scale that is constructed from an amalgam of precision time and planetary rotation then it will also need leaps of some sort. Hopefully they will avoid the attempt to bend a pre-existing time distribution system into doing two different time scales, and simply distribute their calendar days as one of several polynomial offsets from their underlying precision time and frequency distribution system. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
On Sun, Feb 18, 2018 at 2:27 AM, Steve Allen <sla@ucolick.org> wrote:
On Sun 2018-02-18T00:08:25-0700 Brian Inglis hath writ:
Pretty presumptuous of the IAU to use Universal: they /should/ know better.
Alas, Universal Time of 1928 is a subdivision of the already approved Universal Day, and that derives from the Victorian-era knowledge of astronomy and speech patterns of the 1884 International Meridian Conference. Of regrettable things left over from time-keeping history, that is not the worst, and the Germans did explicitly avoid it by choosing Weltzeit as their term.
If Mars denizens decide to choose a single legal time scale that is constructed from an amalgam of precision time and planetary rotation then it will also need leaps of some sort. Hopefully they will avoid the attempt to bend a pre-existing time distribution system into doing two different time scales, and simply distribute their calendar days as one of several polynomial offsets from their underlying precision time and frequency distribution system.
Only if it drifts. Our planet's UT1 drifts with respect to atomic time not because of measurement errors, but because of internal exchanges of angular momentum, predominately due to fluid motions in the liquid outer core. Mars has a fluid outer core; whether or not it actually undergoes significant long period drifts in planetary spin rate remains to be seen. Hopefully, this will be answered by the Insight lander set to go to Mars at the next launch window. (Note - Like Viking and Pathfinder, Insight will not have a DSAC, but will use round trip range and Doppler to measure Mars rotation rate with respect to terrestrial Atomic Time.) Marshall
-- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
participants (5)
-
Brian Inglis -
Marshall Eubanks -
Paul Eggert -
Steve Allen -
Tim Parenti