The Great Refractor

A refractor is a telescope, which uses lenses, in contrast with a reflector telescope, which uses mirrors. A large objective lens, normally consisting of two lenses, produces an optical image. An astronomer can record this image directly at the telescope's focal point with a photoplate or just take a closer look at it through an eyepiece. With 60cm diameter lenses and a focal length of 9m, the Great Refractor of Hamburg Observatory is one of the largest refractors in Germany and one of the 25 largest globally. In the 19th century, refractors with long focal lengths were considered as default observatory equipment. Producing larger and larger lenses caused considerable problems though, so that in the 20th century, reflectors gradually replaced the refractors.

Nevertheless, astronomers in Hamburg used the Great Refractor until the 1980s for different scientific observations, e.g. for studying the Sun's magnetic field or for measurements of the fast radio bursts of pulsars.

 

Fig. 1: The Great Refractor and the interior view of its dome after its substantial renovation in 2019.  © Christian Geisler für Architekturbüro GKKK

Fig. 2: Construction of the dome in 1908

 

Irrigation channels on Mars and Martians

Until 20th century, astronomers recorded their observations in drawings. However, even with large telescopes small details are only visible for short instances because of the inevitable turbulence in the air. This leads to optical illusions andprovides room for the observer's imagination. This is why the astronomers, creating more and more detailed maps of the surface of Mars, often recorded details that did not exist in reality. For example, Schiaparelli “discovered” a pattern of lines on Mars´ surface, which he took to be geological formations. In contrast, his colleague Lowell interpreted the lines as irrigation channels and therefore as proof of intelligent Martians. Only in 1965, with the launch of space probes, did we get an accurate representation of our neighbouring planet. It is a desert landscape littered by craters and volcanos without any irrigation channels, but definitely with various traces of the presence of water in the past. Whilst the existence of simple organisms is still conceivable, a civilization on Mars has never existed.

 

Fig. 1: October 6, 1924 drawn by K. Graff                       

Fig.2: August 27, 2003 STSd, NASA