Dial of a wall-mounted sundial for simultaneous display of temporal (twelve hours, black) and equinoctial (red, digit at end of hour) daytime hours
(At day-night equinox, both types of hours are of equal length.)
An equinoctial hour is one of the 24 equal parts of the full day (which includes daytime and nighttime).
Its length, unlike the temporal hour, does not vary with the season, but is constant. The measurement of the full day with equinoctial hours of equal length was first used about 2,400 years ago in Babylonia to make astronomical observations comparable regardless of the season. Our present hour is an equinoctial hour, freed only from its seasonal variation and from the small error due to some uniform Earth rotation[clarification needed], and realized by modern technical means (atomic clock, satellite and VLBI-Astrometry).
When the temporal hour was used, the daytime and nighttime, whose lengths vary greatly throughout the year, were each divided into 12 hours. This corresponded to the earlier sentiment and custom of not grouping the night with the daytime.
The name equinoctial hours refers to the fact that the temporal hours of the daytime (daylight hours) and those of the night are of equal length at each of the equinoxes.[1]
^Vgl. Friedrich-Karl Ginzel: Handbuch der mathematischen und technischen Chronologie II. S. 308.
night with the daytime. The name equinoctialhours refers to the fact that the temporal hours of the daytime (daylight hours) and those of the night are of...
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Jewish Halachic division of hours. Mechanical clocks encouraged the adoption of equinoctialhours. For the display of temporal hours almost exclusively the...
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including al-Biruni in 1000, subdivided the mean solar day into 24 equinoctialhours, each of which was subdivided sexagesimally, that is into the units...
the markings for the equinoctialhours are a family of straight-line segments, thereby allowing for the measure of equal hours. It is unclear when such...
of 12 daytime hours and 12 nighttime hours, varying in length according to the season. Later,[when?] a system of 24 "equinoctial" hours was used. After...
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at the summer solstice as a measure of latitude. It is stated in equinoctialhours (hōrai isēmerinai), one being 1/12 of the time between sunrise and...
distinguishing characteristic of the equatorial dial (also called the equinoctial dial) is the planar surface that receives the shadow, which is exactly...
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the night [of Sunday 19 May 1000]. The time was approximately eight equinoctialhours after midday on Sunday. Mercury was north of Venus and their latitude...
tree plantings to replace the trees killed by Dutch elm disease. The equinoctial Earth Day is celebrated on the March equinox (around March 20) to mark...
the equinoctial circle. The Arctic Circle E, and the Antarctic Circle F, each 231⁄2 degrees from its respective pole at N and S. The equinoctial colure...
Declination Ecliptic Equatorial coordinate system Equinoctial colure Geographic coordinate system Hour angle Right ascension of the ascending node (RAAN)...
calendar has 146097 days and hence exactly 20871 weeks. The Great Year, or equinoctial cycle, corresponds to a complete revolution of the equinoxes around the...
all 24 hours were of the same length: the two equinoxes. The standard double hour (beru), of equinoctial length, representing two modern hours, of which...
365 days 5 hours 48 minutes and about 56.5 seconds, which is intentionally slightly shorter than the present era mean northward equinoctial year of 365...
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1891. Humboldt, Alexander von, Personal Narrative of Travels to the Equinoctial Regions of America During the Years 1799-1804, (chapter 25). Henry G...
angle (loksos) because it is positioned between the tropical circles and equinoctial circle touching each of the tropical circles at one point ... This Zodiac...
parallel to the Earth's axis will produce sundials whose hour lines show equal hours or legal hours on any day of the year: the dial of Ibn al-Shatir in the...
a kind of stereographic projection of the sphere on the plane of the equinoctial, the eye being supposed to be placed in one of the poles, so that the...
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