Timekeeping on Mars
The problem of synchronization of clocks and calendars on Earth and on Mars became quite acute when the era of exploration of Mars by machines began, because it was necessary to clearly know the flow of solar energy throughout both days and years on Mars. In this article, I propose to consider the existing ways of counting time on Mars.
Since the inclination of the axis of rotation of Mars to the orbital plane differs little from the Earth (23 ° 26'21 "(Earth) and 25 ° 11'24" (Mars)), it undergoes similar seasonal periods, but since the eccentricity of the Mars orbit is much more then the duration of the periods are quite different. Also, if the Martian day is close in duration to the earth, then the duration of the year is different, which further enhances the desynchronization between the calendars.
There are two kinds of days — stellar (sidereal) days lasting 23 hours 56 minutes 4.09 seconds, or 86164.09 seconds, and an average solar day lasting 24 hours or 86400 seconds. They are not equal to each other because in a day, due to the orbital movement of the Earth, the sun shifts against the background of stars. The average solar day is tied to the “fictitious Sun”, since the speed of the Earth’s motion in orbit, and hence the duration of the true solar day, changes throughout the year.
For Mars, the corresponding periods are 24 h 37 min 22.66 s (88642.66 s) and 24 h 39 min 35.24 s (88775.24 s), respectively. As a simple calculation shows, the length of sidereal days on Mars is 2.9% more than on Earth, and the length of solar days is 2.7%.
By international agreement, for vehicles operating on the surface of Mars, the so-called. “Martian sunny day” (Sol) divided into 24 “Martian hours”. Accordingly, the standard of the "Martian second" is 2.7% longer than the earth one. This leads to the fact that the work schedule of operators shifts by 40 minutes every day, and they carry specially designed watches with “Martian time”. There were also other projects of Martian watches. According to one of them, it was proposed to enter the metric time on Mars, setting 10 hours per day, 100 minutes per hour and 100 seconds per minute, on the other, the shortened 25th hour was entered, with a duration of 39 minutes and 35.24 seconds, but these options were rejected. Solo account for spacecraft began with Sol 0 for Viking, Mars Phoenix and MSL Curiosity missions and with Sol 1 for Mars Pathfinder, MER-A Spirit and MER-B Opportunity.
Mars Zero Meridian passes through a small crater, Airy-0, which has coordinates of 5 ° 06′59.99 ″ s. sh. and 0 ° 00′00 ″ c. e. A longitudinal planetocentric standard is used on Mars, in which the longitude varies from 0 ° to 360 ° E Old planetographic standard (0 ° to 360 ° W.) is used on flat maps.
Coordinated Mars time (Coordinated Mars Time, MTC) is analogous to universal time (Universal Time, UT). It is defined as the mean solar time at the prime meridian. The MTC designation can be misleading about the similarity with the UTC standard, but the MTC does not use coordination leap seconds, and the closest terrestrial analogue of the MTC is the UT1 standard. Due to the greater eccentricity of the orbit and other axis tilt, the difference between true solar time (WIS / LTST) and average solar time (CER / LMST) changes much more during the year than on Earth. If on Earth, the time equation (SW = ISV - CER) ranges from “minus 14 min 22 s” to “plus 16 min 23 s”, then on Mars this difference is from “minus 50 min” to “plus 40 min”, which already a lot. In the domestic literature, the reverse difference is often used (HC = CER - WIS). However, solar time should not be confused with zone time, which is only formally related to solar time. There are no time zones in Mars’s habitual form, and of the six rovers, five use local solar time (LMST), and the sixth (Mars Pathfinder) uses true solar time (LTST).
The MTC standard first appeared in the Mars24Sunclock program, created by the Goddard Institute, replacing the AMT (Airy Mean Time) standard, which was a direct analogue to the obsolete GMT standard. The AMT standard is not used in any of the missions because of its lack of accuracy. However, now that there are clear and accurate maps of Mars, the AMT standard may again become relevant.
For the simplicity of astronomical calculations on Earth, the so-called Julian Date (JD) is used, where the zero point is January 1, 4713 BC. e of the Julian calendar or, equivalently, November 24, 4714 BC. e. Gregorian calendar. The first day was number 0. Dates change at noon. A similar date for Mars is set to Sol, which coincides with December 29, 1873 (the date of birth of astronomer Karl Otto Lampland, the first to carry out astrophotography of memory channels on Mars). Other options for reference were 1608 (the invention of the telescope) and the vernal equinox on April 11, 1955.
As above was done with the concept of the day, we will decide what a year is.
The star (sidereal) year is the period of orbital motion around the Sun relative to the “fixed stars”;
Tropical year - a period of full change of seasons or a period during which the sun's longitude varies by 360 ° exactly.
These periods differ by about 20 minutes (tropical less than stellar), which is caused by gyroscopic processes, in particular, by the precession and nutation of the axis of the planets.
The duration of one revolution of Mars around the Sun is about 686.98 solar Earth days, or 668.59 solos. Since the eccentricity of the orbit of Mars (0.0934) is much larger than the earth (0.0167), if we take the period between the equinoxes and solstices during the season, the longest season for the northern hemisphere will be spring (193 sol) and the shortest is autumn (142 sol) .
As well as on Earth on Mars, the tropical year would be the best option for the calendar base, since the precession cycles on Earth and on Mars are long enough to be neglected for relatively short periods of time. The length of the tropical year depends on the choice of the starting point. Usually equinoxes or solstices are chosen as such points. But usually, the spring equinox is used for the Gregorian calendar. Since the Mars orbit is more extended, the differences in the duration of the tropical year are slightly larger than on Earth. If for the Earth the third decimal place differs (from 365.2416 days to 365.2427 days), then for Mars, the second sign differs significantly (from 668.5880 to 668.5958 to sol).
In everyday life, we use the Gregorian calendar, not Julian dates, for the simple reason that the cyclic calendar is much more convenient and useful in everyday life. And therefore, future Martian colonies will need a cyclical calendar. One of the main problems of any calendar is the intercalation of leap year. It is connected with the fact that in a year there is not an integer number of days, and if we do not take into account the amendment for this, then an error between the civil calendar and the tropical year is very fast. One of the variants of such a calendar is the Darius calendar created by aerospace engineer and political scientist Thomas Gangalle. This calendar consists of 24 months for 27-28 days and is based on a ten-year cycle with six leap years for 669 days and four usual ones for 668. This calendar gives an error of 1 sol per 100 years and is quite suitable for current purposes. However, at the moment neither this calendar, nor any other calendar is used, the account goes only for salts.
Since the inclination of the axis of rotation of Mars to the orbital plane differs little from the Earth (23 ° 26'21 "(Earth) and 25 ° 11'24" (Mars)), it undergoes similar seasonal periods, but since the eccentricity of the Mars orbit is much more then the duration of the periods are quite different. Also, if the Martian day is close in duration to the earth, then the duration of the year is different, which further enhances the desynchronization between the calendars.
Day on Earth and Mars
There are two kinds of days — stellar (sidereal) days lasting 23 hours 56 minutes 4.09 seconds, or 86164.09 seconds, and an average solar day lasting 24 hours or 86400 seconds. They are not equal to each other because in a day, due to the orbital movement of the Earth, the sun shifts against the background of stars. The average solar day is tied to the “fictitious Sun”, since the speed of the Earth’s motion in orbit, and hence the duration of the true solar day, changes throughout the year.
For Mars, the corresponding periods are 24 h 37 min 22.66 s (88642.66 s) and 24 h 39 min 35.24 s (88775.24 s), respectively. As a simple calculation shows, the length of sidereal days on Mars is 2.9% more than on Earth, and the length of solar days is 2.7%.
By international agreement, for vehicles operating on the surface of Mars, the so-called. “Martian sunny day” (Sol) divided into 24 “Martian hours”. Accordingly, the standard of the "Martian second" is 2.7% longer than the earth one. This leads to the fact that the work schedule of operators shifts by 40 minutes every day, and they carry specially designed watches with “Martian time”. There were also other projects of Martian watches. According to one of them, it was proposed to enter the metric time on Mars, setting 10 hours per day, 100 minutes per hour and 100 seconds per minute, on the other, the shortened 25th hour was entered, with a duration of 39 minutes and 35.24 seconds, but these options were rejected. Solo account for spacecraft began with Sol 0 for Viking, Mars Phoenix and MSL Curiosity missions and with Sol 1 for Mars Pathfinder, MER-A Spirit and MER-B Opportunity.
Mars Zero Meridian passes through a small crater, Airy-0, which has coordinates of 5 ° 06′59.99 ″ s. sh. and 0 ° 00′00 ″ c. e. A longitudinal planetocentric standard is used on Mars, in which the longitude varies from 0 ° to 360 ° E Old planetographic standard (0 ° to 360 ° W.) is used on flat maps.
Coordinated Mars time (Coordinated Mars Time, MTC) is analogous to universal time (Universal Time, UT). It is defined as the mean solar time at the prime meridian. The MTC designation can be misleading about the similarity with the UTC standard, but the MTC does not use coordination leap seconds, and the closest terrestrial analogue of the MTC is the UT1 standard. Due to the greater eccentricity of the orbit and other axis tilt, the difference between true solar time (WIS / LTST) and average solar time (CER / LMST) changes much more during the year than on Earth. If on Earth, the time equation (SW = ISV - CER) ranges from “minus 14 min 22 s” to “plus 16 min 23 s”, then on Mars this difference is from “minus 50 min” to “plus 40 min”, which already a lot. In the domestic literature, the reverse difference is often used (HC = CER - WIS). However, solar time should not be confused with zone time, which is only formally related to solar time. There are no time zones in Mars’s habitual form, and of the six rovers, five use local solar time (LMST), and the sixth (Mars Pathfinder) uses true solar time (LTST).
The MTC standard first appeared in the Mars24Sunclock program, created by the Goddard Institute, replacing the AMT (Airy Mean Time) standard, which was a direct analogue to the obsolete GMT standard. The AMT standard is not used in any of the missions because of its lack of accuracy. However, now that there are clear and accurate maps of Mars, the AMT standard may again become relevant.
For the simplicity of astronomical calculations on Earth, the so-called Julian Date (JD) is used, where the zero point is January 1, 4713 BC. e of the Julian calendar or, equivalently, November 24, 4714 BC. e. Gregorian calendar. The first day was number 0. Dates change at noon. A similar date for Mars is set to Sol, which coincides with December 29, 1873 (the date of birth of astronomer Karl Otto Lampland, the first to carry out astrophotography of memory channels on Mars). Other options for reference were 1608 (the invention of the telescope) and the vernal equinox on April 11, 1955.
Year on Earth and Mars
As above was done with the concept of the day, we will decide what a year is.
The star (sidereal) year is the period of orbital motion around the Sun relative to the “fixed stars”;
Tropical year - a period of full change of seasons or a period during which the sun's longitude varies by 360 ° exactly.
These periods differ by about 20 minutes (tropical less than stellar), which is caused by gyroscopic processes, in particular, by the precession and nutation of the axis of the planets.
The duration of one revolution of Mars around the Sun is about 686.98 solar Earth days, or 668.59 solos. Since the eccentricity of the orbit of Mars (0.0934) is much larger than the earth (0.0167), if we take the period between the equinoxes and solstices during the season, the longest season for the northern hemisphere will be spring (193 sol) and the shortest is autumn (142 sol) .
As well as on Earth on Mars, the tropical year would be the best option for the calendar base, since the precession cycles on Earth and on Mars are long enough to be neglected for relatively short periods of time. The length of the tropical year depends on the choice of the starting point. Usually equinoxes or solstices are chosen as such points. But usually, the spring equinox is used for the Gregorian calendar. Since the Mars orbit is more extended, the differences in the duration of the tropical year are slightly larger than on Earth. If for the Earth the third decimal place differs (from 365.2416 days to 365.2427 days), then for Mars, the second sign differs significantly (from 668.5880 to 668.5958 to sol).
The calendar
In everyday life, we use the Gregorian calendar, not Julian dates, for the simple reason that the cyclic calendar is much more convenient and useful in everyday life. And therefore, future Martian colonies will need a cyclical calendar. One of the main problems of any calendar is the intercalation of leap year. It is connected with the fact that in a year there is not an integer number of days, and if we do not take into account the amendment for this, then an error between the civil calendar and the tropical year is very fast. One of the variants of such a calendar is the Darius calendar created by aerospace engineer and political scientist Thomas Gangalle. This calendar consists of 24 months for 27-28 days and is based on a ten-year cycle with six leap years for 669 days and four usual ones for 668. This calendar gives an error of 1 sol per 100 years and is quite suitable for current purposes. However, at the moment neither this calendar, nor any other calendar is used, the account goes only for salts.
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Source: https://habr.com/ru/post/215387/
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