Today I Learned (TIL)

461 readers

1 users here now

Rules

Posts must begin with "TIL".
Posts must be about a specific fact. No "TIL about [ducks]."

founded 1 year ago

MODERATORS

Ullallulloo@civilloquy.com

186

TIL Roman hours were not a fixed length of time but always just ¹⁄₁₂th of the daytime, so during the summer an hour could be 1½ modern hours while during the winter it could only be 40 minutes (archive.org)

submitted 1 year ago* (last edited 1 year ago) by Ullallulloo@civilloquy.com to c/todayilearned@civilloquy.com

11 comments fedilink hide all child comments

Roman hours were not of a fixed length because they simply equal to the amount of light or darkness on a given day divided by twelve. Since the amount of daylight varies greatly from day to day over the course of the year—with perhaps as many as 15 hours of daylight in the summer and only 8 or 9 in the winter—a Roman hour in the summer might be equivalent to a modern hour and a half, and, similarly, in the winter, a Roman hour might be only 40 of our minutes long.

you are viewing a single comment's thread
view the rest of the comments

[–] jmcs@discuss.tchncs.de 35 points 1 year ago (1 children)

That's almost a necessity if you use a sun clock as your primary time measurement device.

[–] Nouveau_Burnswick@lemmy.world 6 points 1 year ago (1 children)

How so?

Before the sundial, the day was just before noon and after noon. The 12 hour day (and 12 hour night) came in once they had sundials, 263 BC.

Sundials do not need calibration for latitude or day length. Romans made a conscious choice to have 12 day and 12 night hours rather than sunrise and sunset at different times throughout the year.

[–] jmcs@discuss.tchncs.de 3 points 1 year ago (1 children)

See https://www.macmillanhunter.co.uk/time/measurement-of-time/what-is-the-equation-of-time/ for an explanation, and how it's corrected on sun dials.

[–] Nouveau_Burnswick@lemmy.world 2 points 1 year ago

That's super cool, but it's just a distortion of time on a sundial, it's not a purposeful distortion of hours. Nor does it align with the summer and winter hours (the distortions are offset from the solstices).