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Tshese conventions do not require a reference to equivalent Terran dates, so an epoch may be assigned at any time that is appropriate in the Martian calendar. |
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The question of appropriateness concerns the goals of the calendar. Some users will argue that the Martian calendar concerns only events that occur on Mars and concerns only those events that are specifically datable. This view would tend to choose a very late epoch, probably around A.D. 1970, just prior to the launchings of probes to Mars. |
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Others will argue that the calendar should be able to represent from a Martian perspective any specifically datable event in human history, so that future Martian historians can use a single calendar. This view would tend to an earlier epoch, perhaps coinciding with the start of the Julian Day number. The utility of this latter view depends in large part upon the difficulty of producing meaningful date conversions between the Terran and Martian systems. |
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It is possible to perform some rough-and-ready calculations in this area. Using approximate sidereal periods of 365 and 687 days for Earth and Mars, respectively, you can see that 687/365 = 1.88, the ratio of Martian to Terran year length. Assuming that today is roughly A.D. 2000, the start of the Julian Day system occurred (2,000 (4,712)) or about 6,712 Terran years ago. This period of time is roughly equal to 6,712/1.88 = 3,570 Martian yars. Hence, if both linear scales started simultaneously, the current Martian yar number would be in the neighborhood of A.M. 3570. This result means that you would spend about 10% of the capacity of the Martian calendar to achieve the ability to represent virtually all historical dates of human significance. This is a good trade-off. |
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The assignment of an epoch also needs to recognize the following factors: |
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Martian time zones. Martian longitude 0 is analogous to the Greenwich Meridian. There is thus a dateline at longitude 180. Hence, MD# 1 should be assigned such that datable events do not occur in the previous day anywhere on Mars. |
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Seasons. Some may wish that Martian solstice and equinox dates generally occur during months corresponding to the Terran months in which Terran solstices and equinoces occur. This correspondence is certainly not a requirement, as you have seen. |
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You may also wish that mensar 1 be a winter month in the northern Martian hemisphere, just as January is a winter month in the Terran northern hemisphere. Again, this correspondence is not critical but would constrain the assignment of epoch. This study of calendars has shown that the choice of New Year's date is not arbitrary but is certainly varied in human cultures. |
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Given that there are good reasons for selecting the southern Martian hemisphere as a place to initiate colonization, the choice of the northern hemisphere as the standard for relating seasons to calendar mensars may be a poor idea. |
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In summary, several factors make any correspondence of mensars and seasons quite arbitrary. Hence, you simply may want to avoid making any deliberate correspondence. |
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