Saturn observation reveals a new orbiting body

Titan's detection revealed that Saturn, like Jupiter, has a substantial family of orbiting objects.

Huygens's observational work linked improvements in telescopes with discoveries beyond Earth.

Cassini detected a moon later called Iapetus while observing Saturn.

Iapetus joined Titan among the known satellites of Saturn.

Cassini's later observations found the moon much easier to see on one side of Saturn than the other.

The first edition laid out laws of motion and universal gravitation.

The new work used the same gravitational principle to explain motion on Earth and in the heavens.

Newton presented mathematical arguments for orbital motion and other celestial phenomena.

Publication supplied tools for calculating motions of planets and comets, though later work refined them.

NASA's UTC catalog dates the transit to 6 June; some observers described it as 5 June in their local time.