Jupiter possesses four large moons: Io, Europa, Ganymede, and Callisto. These are called the Galilean Moons. They are easy to observe and the first objects found to orbit a planet other than the Earth.

Flat-Earthers are often seen demanding proof that an object can orbit another object. All they have to do is to use a telescope to observe Jupiter and its Galilean moons.

Galilean moons are first observed by Galileo Galilei in 1610, hence the term ‘Galilean moons’. These are the first evidence that an object can orbit an object other than the Earth. It is one of the first discoveries that lead to heliocentrism, that the planets are in motion around the Sun in the center of the solar system.

We can observe Jupiter effortlessly using the naked eye. Galilean moons themselves have the magnitude of 4.6-5.6 and are bright enough to be seen by naked eye. But because of their proximity to the much brighter Jupiter (-2.9), it is harder to see them. Under the right conditions, we can observe them by obscuring Jupiter by our little finger. If a binocular or a telescope is available, it would be much easier to observe the Galilean moons.

The four Galilean moons have relatively short orbital periods, between 1.8 days (Io) to 16.7 days (Callisto). By making two separate observations only a day apart, we can readily tell that the moons have changed place.

Jupiter and its Galilean moons are firsthand evidence that there can be an object orbiting another object other than the Earth, precisely as demanded by flat-Earthers. To perform this simple observation, it is not necessary to have expensive equipment, extended time commitment or detailed knowledge of the topic.

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