BC to AD Calculator
Converted Year
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| Historical Era | Astronomical Year |
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Understanding the Systems
Historians typically move from 1 BC directly to 1 AD. Astronomers calculate time linearly, inserting a "Year 0" to simplify math.
$$ \text{Astronomical} = \begin{cases} \text{Year} & \text{if AD} \\ 1 - \text{Year} & \text{if BC}
\end{cases} $$
Example: 1 BC in history is Year 0 in astronomy. 2 BC is Year -1.