The astrolabe of Ephemeris is a large, ornate astrolabe made by Queen [[Ephemeris]] of [[New Equestria]]. A powerfully enchanted artifact, Ephemeris used it on her various military campaigns in the future territory of New Equestria. Unfortunately, an accident involving it killed her in 3027 AE. The astrolabe, rumored to have been cursed, was sealed in the catacombs of the [[Temple of the Undying Sun]] in [[New Canterlot]] for safekeeping. This has mostly been without incident over the last three centuries, although one pony was killed by it while participating in triumphal rituals. Future presumptive triumphators have been cautioned against approaching the Astrolabe while in the catacombs, and a warning sign was added to remind them.

The astrolabe is about 25 cm in diameter. It has a rotating rete and rule. The rete shows ordinary Equine constellations. Contemporary accounts portray Ephemeris as adjusting the astrolabe to produce various effects, but no detailed information on its use is known to exist - apparently, knowledge of its operation died with its creator. 

Experimentation has occasionally been suggested to the custodians of the astrolabe, but such suggestions have not been received favorably. During the reign of king [[Day Star]], the cantankerous [[Archimandrite]] Minister-Twotongues-is-a-Heartless-Wretch-ius received a parliamentary request for information about the feasibility of having the military research the astrolabe. He responded laconically: "It is unfeasible; we haven't enough canopic jars for all of them."

The Astrolabe of Ephemeris is the prison for a lesser [[draconequus]], who was magically bound by Ephemeris to power the artifact.