September 22 – Asteroid 57 Mnemosyne

Discovered on this very day in 1859 by Robert Luther, 57 Mnemosyne is a main belt asteroid of about 113km across, sweeping round the Sun at 16.7km/s,  and taking about five and a half years to complete one orbit. Mnemosyne is a stony “S” type asteroid, with an albedo of 0.215. S types are generally brighter than most, with Iris able to reach +7.0 at opposition.

Mnemosyne was a titaness (a daughter of Uranus and Gaia),  and was mother of the nine Muses (Zeus was the father, and somehow managed to persuade Mnemosyne that they needed to sleep together for nine nights to get the job done).

It is from Mnemosyne that we get the word mnemonic.


1862  –  Asteroid 75 Eurydike discovered by C H F Peters.

Orpheus and Euridice, by Christian Gottlieb Kratzenstein.

Orpheus and Euridice, by Christian Gottlieb Kratzenstein.


1878  –  Asteroid 190 Ismene, a member of the Hildian family, discovered by C H F Peters. The family are named after asteroid 153 Hilda.


1884  –  Asteroid 242 Kriemhild discovered.


2004  –  Planetoid 120347 Salacia discovered.  Salacia has an incredibly high number, but is significant because, as you will have noticed, I used the word “planetoid”, indicating it isn’t one of my normal day-to-day asteroids.  This particular Kuiper belt object is estimated to be 850 km (530 miles) in diameter.


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