The known Universe consists of only 8 bodies:

1
Before 1600
The known Universe consists of only 8
bodies Earth, Sun, Moon, Mercury, Venus, Mars,
Jupiter, Saturn.
Earth is thought to be the centre of the Universe
with all other bodies orbiting it. (Ptolemaic
system)
2
Development of the Copernican system
Problem with the Ptolemaic Universe some of the
planets seem to move in the wrong direction in
the sky.
Can only be explained if the Earth and the other
planets orbit the Sun Copernican theory
3
The Discovery of Uranus 1781 William Herschel
During sky survey spotted a faint star that
appeared disc like in the constellation of Gemini
(near the ecliptic). Further observations
revealed its motion and orbit.
4
The Discovery of Neptune 1846 Peturbations in
Uranus' orbit suggests another planet lies beyond
Uranus. Adams and Le Verrier predict an orbit
and a search conducted by Encke discovers the new
planet at the predicted location.
5
The Discovery of Pluto Further peturbations in
Uranus' orbit measured by Percival Lowell and
Edward Pickering suggests another the existence
of another mysterious planet. American student
Clyde Tombaugh eventually discovers Pluto in a
photograph in 1930.