Radar observations of 101 Helena were made from the Arecibo Observatory in what year?
101 Helena 101 Helena is a rocky main-belt asteroid. It was discovered by Canadian-American astronomer J. C. Watson on August 15, 1868, and was named after Helen of Troy in Greek mythology. Radar observations were made of this object on Oct 7 and 19, 2001 from the Arecibo Observatory. Analysis of the data gave an estimated ellipsoidal diameter of 71×63×63 ± 16% km. The diameter estimated from IRAS infrared measurements is 66 km. It is classified as an S-type asteroid in the Tholen system.
Guido d'Arezzo (crater) Guido d'Arezzo is a crater on Mercury. It has a diameter of 66 kilometers. Its name was adopted by the International Astronomical Union in 1976. Guido d'Arezzo is named for the Italian music theorist Guido of Arezzo, who lived from 990 to 1050.