Definition
Latin. In old English law, a solar day — the period from sunrise to sunset — as distinguished from dies lunaris, a lunar day. Together, the solar day and the lunar day composed what medieval legal sources called the "artificial day," a unit of time used in reckoning legal deadlines, pleading periods, and procedural terms. The artificial day in this framework was not simply the twenty-four hour clock period we default to today, but a structured concept built from the combination of these two components. The term appears in Bracton's De Legibus et Consuetudinibus Angliae as part of his treatment of temporal computation in legal proceedings.
Common Confusion
DIES SOLARIS should not be confused with the broader term DAY as used in modern legal instruments. The modern legal "day" is almost universally understood as a calendar day running from midnight to midnight (or occasionally from sunrise to sunrise), and the old distinction between dies solaris and dies lunaris has no operational role in contemporary practice. Researchers encountering this term in historical materials should not assume it maps cleanly onto any modern day-counting rule. Similarly, dies solaris is distinct from dies juridicus (a day on which courts may sit) and dies non juridicus (a day on which they may not) — a separation based on court function rather than astronomical division.
Why It Matters in Research
Dies solaris is an archaic technical term with no living legal force. Its significance to Law Mind corpus researchers is entirely historical and interpretive.
The primary trap is anachronistic reading. When medieval pleading records or treatises reference time periods or deadlines using the artificial day framework, modern researchers accustomed to calendar-day computation may misread what period was actually meant or how it was calculated. The Bracton source underlying all three dictionary entries (fol. 264) is the essential reference point; researchers working with pre-modern English procedural materials should consult Bracton directly rather than relying on the dictionary summaries alone.
The term rarely appears in isolation. It surfaces as part of a cluster of related dies terminology — dies solaris, dies lunaris, dies juridicus, dies non, dies utiles, dies communes — and understanding any one of them requires understanding how medieval legal sources organized time more broadly. A researcher who encounters dies solaris without context for the artificial day framework will find the definition technically accurate but practically incomplete.
No jurisdictional variation is meaningful here. The term is confined to medieval English legal usage and does not migrate into American law in any operative sense. It appears in American legal dictionaries only for completeness and as an aid to historical research.
Historical Dictionary Support
Black's, Rapalje & Lawrence, and Burrill are in complete agreement on this term — each defines it identically as a solar day distinguished from dies lunaris, with both composing an artificial day, and all three cite Bracton fol. 264 as the authority. The uniformity reflects the fact that all three are drawing from the same narrow Latin-law tradition with no meaningful divergence in the sources available to them.
What the dictionaries do not supply is any explanation of how the artificial day was actually used in practice — how the solar and lunar components interacted in computing legal periods, what procedures depended on the distinction, or whether the framework had any meaningful application beyond Bracton's theoretical exposition. Researchers should treat the dictionary entries as identifiers, not as substantive guides to medieval time-reckoning. For that, Bracton's own text and secondary scholarship on medieval English procedure are necessary.
Burrill's entry is marginally more precise in its framing ("L. Lat. In old English law"), correctly signaling that this is a Latin-law term of limited English application rather than a concept imported into general common law usage.