First ideas about Universe up to now

Confirming The Big Bang (The Hubble telescope)

1990 BCE

The Hubble Space Telescope (HST) was launched into orbit around the Earth in 1990, and remains in operation.

At present/Nowadays (The Big Bang Theory)

1931 BCE

In 1931, Lemaître proposed that the universe began with a "explosion" and took cosmic rays to be the remnants of the event.
Later on, during a BBC radio broadcast on 28 March 1949, Fred Hoyle coined the name of Lemaître's theory such as "this 'big bang' idea".

In the middle ages (Copernicus)

1543 BCE

the Sun is in the center of the Universe, motionless, with Earth and the other planets moving around it in circular paths

Ancient Greeks (Ptolemy)

100 BCE

the Universe consisted of a flat Earth (or a square one, a zigarrut, etc.) surrounded by the Sun, the Moon, and the stars.