February 10: Eugène Michel Antoniadi

Eugène Michel Antoniadi

March 1, 1870 – February 10, 1944

Eugène Michel Antoniadi was a Greek astronomer who spent most of his life in France. His first publications date from the late 1880s, and his last ones from 1941 or 1942. He is best known for his work concerning the planets Mars and Mercury, and drew the best pre-Space Age maps of them, despite the fact that his first attempts to draw a map of Mercury were flawed by his incorrect assumption that Mercury had synchronous rotation with the Sun.

He became a highly reputed observer of Mars, and at first supported the notion of Martian canals. In 1909, using the great 83-cm aperture refracting telescope of the Meudon Observatory near Paris under ideal observing conditions, he demonstrated that the so-called “canals” of Mars were optical illusions.

He is also famed for creating the Antoniadi scale of seeing, which is commonly used by amateur astronomers. Now the scale is seen as the metric system of astronomy, being used as a default measurement all over the world.

The scale is on a 5 point system, with one being the best seeing conditions and 5 being worst. The actual definitions are as follows:

I.   Perfect seeing, without a quiver.

II.  Slight quivering of the image with moments of calm lasting several seconds.

III. Moderate seeing with larger air tremors that blur the image.

IV. Poor seeing, constant troublesome undulations of the image.

V.  Very bad seeing, hardly stable enough to allow a rough sketch to be made.

Note: the scale is usually indicated by use of a Roman numeral.

Antoniadi was also a noted historian, as well as a superb artist, writing about the pyramids and Egyptian astronomy. In the early twentieth century he further demonstrated his skills as an architect by compiling a great three-volume work on the mosque of St Sophia in Constantinople (now Istanbul). He was also a strong chess player. His best result was equal first with Frank Marshall in a tournament in Paris in 1907, a point ahead of Savielly Tartakower.

A crater on Mars and the crater Antoniadi on the Moon were named in his honor, as well as Antoniadi Dorsum on Mercury itself.