1781 -  William Herschel sees what he at first thinks is a comet.  However, it is shaped like a disc and orbits the Sun beyond Saturn.  He declares it a planet.  It is the first planet discovered by using a telescope.  

1787 -  Herschel discovers the moons Titania and Oberon.

1829 -  Observers find that Uranus is tilted on its side.

1851 -  English astronomer William Lassell discovers the moons Ariel and Umbriel.

1948 -  Astronomer Gerard Kuiper discovers the last of the five major moons, Miranda.