Discovery of Galilean Moons by Galileo Galilei

As a result of improvements Galileo Galilei made to the telescope, he was able to see celestial bodies more distinctly that was ever possible before. On January 7, 1610 he turned his newly developed telescope to Jupiter.

He discovered four objects orbiting the giant planet. It took him another night’s observations to clearly distinguish between two of them.

He called them ‘The Medicean Planets’ after the Medici family and gave them numbers.

Having previously been encouraged in his other scientific studies by the Church in Rome Galileo made his findings known to the Pope. Much of his disappointments, the Church soon took exception to his assertions that Earth was not the center of the universe and forbade his to continue his research or to even discuss it openly.

It was nearly 250 years later before they were given names: Io, Europa, Ganymede and Callisto. Galileo initially named his discovery the Cosmica Sidera but names that eventually were chooses by Simon Marius.

Galileo’s discovery proved the importance of the telescope as a tool for astronomers by showing that there were objects in space to be discovered that until then had remained unseen by the naked eye.
Discovery of Galilean Moons by Galileo Galilei 

Seleucus of Seleucia: Discovery of tides being caused by the moon

The connection among tides, moon and sun has been known since ancient times. Pytheus of Marseilles was the first of the Greek astronomers to correctly related and record the movement of the tides with the phases of the moon. He sailed to northwestern Europe and circumnavigated Great Britain in 325 BC.

Along documenting polar ice and the midnight sun that does not set in the far north on the summer Solstice, Pytheus also reported that the moon caused the tides.

The link between tides and the moon was first theorized by Seleucus of Seleucia in the 2nd century. He speculated that the tides were caused by the motions of the moon.

Seleucus of Seleucia, the Babylonian astronomer wrote that the rising and falling of tides were the result of the attractions of the moon and that the height of the tides depends on the location of the moon relative to the sun.

Born in the Babylonian town of Seleucia, he is today primarily remembered as the only known supporter of Aristarchus's heliocentric theory, maintaining that it accurately described the physical structure of the universe.

According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning, but it is not known what arguments he used. Seleucus’ arguments for a heliocentric theory were probably related to the phenomenon of tides.
Seleucus of Seleucia: Discovery of tides being caused by the moon