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The first thing you have to remember is that we count the days a bit differently. Having 39.6 more minutes each day, and 669 days—or sols, as we call ’em—in a sidereal period, meant that aresians threw out both Greenwich Mean Time and the Gregorian calendar in a.d. 2032, long before the Pax Astra took control of the near-space colonies, way before Mars declared its independence. The Zubrin calendar has twelve months, ranging from 48 to 66 sols in length, each named after a Zodiac constellation; it retroactively began on January 1, 1961, which became Gemini 1, m.y. 1 by local reckoning. The conversion factors from Gregorian to Zubrin calendars are fairly complex, so don’t ask for an explanation here; best to say that one of the first things newcomers from Earth have to realize is that April Fool pranks are even less funny at Arsia Station than they were back in Indiana.
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Allen M. Steele (Sex and Violence in Zero-G: The Complete "Near Space" Stories, Expanded Edition)