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One of the small southern constellations introduced by the Frenchman Nicolas Louis de Lacaille after he mapped the southern stars in 1751–52. Lacaille wrote that the constellation represented a pendulum clock beating seconds, as used for timing his observations. Lacaille introduced it under the French name l’Horloge, but this was Latinized to Horologium on the second edition of his chart in 1763.

The clock was imagined with a fully marked dial and even a seconds-hand, a remarkable feat for an area of sky that contains a sparse scattering of stars no brighter than fourth magnitude. In some representations its brightest star, Alpha Horologii, marks the clock’s pendulum, as in Bode’s illustration here, while others such as Lacaille himself placed Alpha on one of the weights.

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Horologium, shown as Horologium Pendulum, in the Uranographia of Johann Bode (1801). For Lacaille’s original depiction, see here.



© Ian Ridpath. All rights reserved


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