The Urania Society was founded by Foerster in 1888 as a popular scientific society, in Invalidienstraße, and it had an astronomical section with its own observatory .
The main instrument was a 5 meter long, 314 millimeter refractor, built by Carl Bamberg in Berlin which, at the time, was the second-largest refractor in Germany. Gustav Witt used this, in 1898, to discover Eros (asteroid No 433), which he observed to be moving very fast.
The reason for this, it transpired, was that Eros was following an orbit not seen before. All previous asteroids had been orbiting between Mars and Jupiter, but Eros was found to be orbiting within Mars for most of its period, and would actually approach within 23 million kilometers (0.15 AU) of Earth. It was quite close to Earth when Witt had observed it. It was the first asteroid to receive a masculine name.
Witt had discovered Eros in a manner fairly common in Science - i.e. by mistake, when he was really looking for something else, in this case another asteroid, Eunike. Eros has been useful to astronomers for calculating, among other things, the Sun-Earth distance and the combined Earth-Moon mass.
(On the same night as Witt, A. Charlois observed the asteroid from Nice, although Witt was the first to announce the discovery)
About 20 years later, the Observatory was taken over by the University as a training telescope and was destroyed in the Second World War, although various of their instruments ended up elsewhere in Berlin. Also destroyed, in 1944, was the Zeiss-Planetarium am Bahnhof Zoo, which had been opened in 1926.
- was the 433rd asteroid to be discovered.
- By virtue of its unusual behavior, it was a given a masculine name. Up until then and for a long time after, only feminine names were used.
- It approaches close to Earth about every 40 years, when it becomes the sixth brightest asteroid.
- During its orbit, the brightness varies noticeably due to the rotation of its irregular, elongated shape.
- Its dimensions are approx. 38km x 13km x 13km. This about twice the size of the nucleus of Halley's Comet, but of a similar relative shape. It is one of the largest near-Earth asteroids.
- It rotates on its axis with a period of 5.27 hours
- It was the first of a new class of asteroid - the Amor class. Amor-types orbit within the Martian orbit but not the Earth's.
- Its gravity is such that a person weighing 100 kgs. on Earth would weigh about 50 grams on Eros.
On 17. February 1996 The Near Earth Asteroid Rendezvous (NEAR) spacecraft was launched to reach Eros in January 1999. NEAR encountered Eros in December 1998, but a failure of its motor aborted the planned January 10th 1999 rendezvous. Instead of entering orbit around the asteroid, NEAR could only make a fly-by. It had to circle the Sun, and rendevoused on February 14 2000.
On Monday, 12 February 2001, it touched down on Eros, after transmitting 69 close-up images of the surface during its final descent.