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Nocturnal
Video   Text

 

At night, the stars seem to revolve uniformly around a fixed point—the celestial north pole—in 23 hours and 56 minutes. Because of the four-minute advance of diurnal rotation, the following day at the same hour the visible stars appear to have shifted slightly westward.

The accumulation of the daily shifts entails, in a full year, a further complete uniform rotation of the stars around the celestial pole.

Beginning in the 15th C., the annual and diurnal apparent rotations of the stars were used to determine the hour of night thanks to an instrument known as a nocturnal, or nocturnlabe, built in different versions.

One side of the instrument records the months and days of the year or an equivalent zodiacal calendar. Holding the handle of the nocturnal perpendicular to the ground, the user aims at the celestial north pole, identified for simplicity's sake with the Pole Star in the constellation of Ursa Minor, Little Dipper, through the hole of the central rivet.

Next, the user places another disk, bearing an hour quadrant, in such a way that the related index intercepts the tack for the current day on the underlying calendar. The hour quadrant is thus oriented with respect to the stars.

Lastly, the user rotates a second index, placing it so that, when aimed at the Big Square, in Ursa Major, Big Dipper, it grazes the first two stars.

At this point, just like a watch hand, the index intercepts the hour of night on the quadrant.

Objects
Astronomical compendium

Astronomical compendium

Inv. 2478
Maker unknown, German, late 16th cent.

Astronomical compendium

Astronomical compendium

Inv. 2481
Maker unknown, German, ca. 1600

Horary quadrant

Horary quadrant

Inv. 2499
Stefano Buonsignori, Florence, ca. 1580

Lunar converter

Lunar converter

Inv. 3701
Maker unknown, Italian, 17th cent.

Nocturnal

Nocturnal

Inv. 1313
Maker unknown, Italian, first half 17th cent.

Nocturnal

Nocturnal

Inv. 2494
Maker unknown, Italian, late 16th cent. - early 17th cent.

Nocturnal

Nocturnal

Inv. 2500
Maker unknown, English, 16th cent.

Nocturnal

Nocturnal

Inv. 2493
Maker unknown, Italian, mid-17th cent.

Nocturnal

Nocturnal

Inv. 2501
Maker unknown, French, 1554

Nocturnal

Nocturnal

Inv. 2502
Pineau [attr.], French, ca. 1600

Nocturnal

Nocturnal

Inv. 2504
Maker unknown, French, 1560

Nocturnal and sundial

Nocturnal and sundial

Inv. 2498
Georg Zorn, Augsburg, 1613

Nocturnal and sundial

Nocturnal and sundial

Inv. 1305
Lorenzo della Volpaia, Florence, 1511

Nocturnal and sundial

Nocturnal and sundial

Inv. 3264
Eufrosino della Volpaia, Florence, 1520

Nocturnal and sundial

Nocturnal and sundial

Inv. 3811
Girolamo della Volpaia, Florence, 1567

Nocturnal and sundial

Nocturnal and sundial

Inv. 2503
Girolamo della Volpaia, Florence, 1568

Nocturnal and sundial

Nocturnal and sundial

Inv. 1286
Girolamo della Volpaia [attr.], Florence, 16th cent.

Perpetual calendar

Perpetual calendar

Dep. MA, Firenze
Christian Boyling, Dresden, second half 17th cent.