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Qualify Year Zero statement.
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@ -505,7 +505,7 @@ F_n = \frac{\varphi^n-(-\varphi)^{-n}}{\sqrt 5} = \frac{\varphi^n-(-\varphi)^{-n
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Date and time calculations are challenging for a number of reasons: What is the correct granularity for an integer to represent? What value should represent the starting value? How should time zones and leap seconds be handled?
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One particularly complicating factor is that there is no [Year Zero](https://en.wikipedia.org/wiki/Year_zero); 1 B.C. is immediately followed by A.D. 1.
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The Julian date system used in astronomy differs from standard time in this regard.
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(The date systems used in astronomy [differ](https://en.wikipedia.org/wiki/Julian_day#cite_note-7) from standard time in this regard, for instance.)
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In computing, absolute dates are calculated with respect to some base value; we refer to this as the _epoch_. Unix/Linux systems count time forward from Thursday 1 January 1970 00:00:00 UT, for instance. Windows systems count in 10⁻⁷ s intervals from 00:00:00 1 January 1601. The Urbit epoch is `~292277024401-.1.1`, or 1 January 292,277,024,401 B.C.; since values are unsigned integers, no date before that time can be represented.
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