File:Ancient Roman time keeping hora hora noctis vigilia length.png

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English: Lengths of 1/12 of the day, 1/12 of the nigth and 1/4 of the nigth corresponding respectively to ancient Roman hora (hours: hora prima, secunda, tertia etc), hora noctis (night hours: hora prima noctis, hora secunda noctis, hora tertia noctis etc) and vigilia (derived from watches: vigilia prima, secunda, tertia and quarta).

The surise and sunset times for this diagram are calculated for Forum Romanum 41°53′33″N 12°29′07″E / 41.892426°N 12.485167°E / 41.892426; 12.485167 AD 8 (the Julian calendar). Sunrise and sunset times are used as boundaries of day and night. Many sources however are ambiguous because of confusing terms sunrise with dusk and sunset with dawn. This is important, because times of dusk and dawn differ significantly from times of sunrise and sunset. The semidiameter of the sun and atmospheric refraction are taken into account. Equinoxes and solstices are computed too, not set by Romans.

Sunrise and sunset times, sun azimuths and altitudes, dates and times of equinoxes and solstices were calculated using algorithms from:
Jean Meeus, Astronomical algorithms, Second English Edition, Willmann-Bell, Inc., Richmond, Virginia, 1998, With corrections as of August 10, 2009, ISBN 0-943396-61-1.
There is an online calculator also based on Astronomical Algorithms, by Jean Meeus, computing sunrise and sunset times, sun azimuths and elevations:
http://www.esrl.noaa.gov/gmd/grad/solcalc/ NOAA Solar Calculator
(Gregorian calendar)

however calculations for this image are based directly on this Meeus's book.
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Author Darekk2

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Date/TimeThumbnailDimensionsUserComment
current13:38, 11 March 2016Thumbnail for version as of 13:38, 11 March 2016800 × 1,312 (157 KB)Darekk2 (talk | contribs)equinoxes and solstices
03:54, 11 March 2016Thumbnail for version as of 03:54, 11 March 2016800 × 1,312 (155 KB)Darekk2 (talk | contribs)labels of seasons positions
03:28, 11 March 2016Thumbnail for version as of 03:28, 11 March 2016800 × 1,312 (155 KB)Darekk2 (talk | contribs)corrected the grid ...
19:02, 10 March 2016Thumbnail for version as of 19:02, 10 March 2016800 × 1,312 (155 KB)Darekk2 (talk | contribs)replace O h by 0 h
18:55, 10 March 2016Thumbnail for version as of 18:55, 10 March 2016800 × 1,312 (155 KB)Darekk2 (talk | contribs)replaced word length by duration
18:40, 10 March 2016Thumbnail for version as of 18:40, 10 March 2016800 × 1,312 (155 KB)Darekk2 (talk | contribs)User created page with UploadWizard

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