Star Tales – Custos Messium

Introduced by the French astronomer Joseph Jérôme de Lalande on his celestial globe of 1775, and described in an accompanying pamphlet titled Explication des nouveaux globes céleste et terrestre (see this review from the Journal des Sçavans of 1776 November). The name Custos Messium is a punning reference to his countryman Charles Messier, the famed comet hunter, and in fact the constellation was often known as Messier, particularly in France. Its brightest star was of 4th magnitude.

Custos Messium lay in what is now northern Cassiopeia, between Cepheus and Camelopardalis, next to another subsequently abandoned constellation, Rangifer the Reindeer. Lalande chose this previously anonymous area of sky because it was here that the comet of 1774 was first seen. The comet was extensively observed by Messier but, ironically, was not discovered by him – the discoverer in this case was actually another Frenchman, Jacques Montaigne.

Right: Custos Messsium, seen beside Rangifer the reindeer in the Uranographia of Johann Bode (1801).

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