Galilean moons century when other inner moons were discovered, and Marius' names became widely used. Galileo was able to develop a method of determining longitude based on the timing of the orbits of the Galilean moons. The times of the eclipses of the moons could be precisely calculated in advance, and compared with local observations on land or on ship to determine the local time and hence longitude. The main problem with the technique was that it was difficult to observe the Galilean moons through a telescope on a moving ship; a problem that Galileo tried to solve with the invention of
Folk instrument Folk instrument A folk instrument is a musical instrument that developed among common people and usually does not have a known inventor. It can be made from wood, metal or other material. Such an instrument is played in performances of folk music. The instruments can be percussion instruments, or different types of flutes or trumpets, or string instruments that are plucked, hammered or use a form of bow. Some instruments are referred to as folk instruments because they commonly appear in folk music, even though they do not meet the criteria defining a folk instrument; an example is the harmonica.