This is a continuation of that notebook about the geo-heliocentric system proposed by Tycho Brahe, known as the Tychonic system.

Tychonic system vs. Heliocentric system

The Tychonic system is a model of the Universe that was proposed by Tycho Brahe in the late 16^th century. In his model, the Earth (🜨) is at the centre of the universe, the Moon (☾), the Sun (⊙) and the stars revolve around the Earth, while the other planets (Mercury ☿, Venus ♀, Mars ♂, Jupiter ♃, and Saturn ♄) revolve around the Sun.

The loops of Mars

With the geo-heliocentric configuration, if you follow the path of Mars, you can easily recognise a pattern similar to that drawn by Johannes Kepler in Astronomia Nova (refer to the illustration below). These "loops of Mars" are showcased in the following visualization. Note that the sizes of the orbits and speeds of the planets are not to scale.

The apparent retrograde motion of Mars sporadically forms loop-like patterns in the night sky when its positions against the backdrop of stars are compared over several consecutive nights.

These loops, which are more obvious with Mars than with the other planets of our solar system, puzzled Tycho Brahe for many years. Eventually, it was Johannes Kepler who was able to elucidate their origin thanks to the heliocentric system.