Simplify the following text for a Grade 11 native English-speaking person.
Original: Proper motion was suspected by early astronomers ( according to Macrobius , AD 400 ) but proof was provided in 1718 by Edmund Halley , who noticed that Sirius , Arcturus and Aldebaran were over half a degree away from the positions charted by the ancient Greek astronomer Hipparchus roughly 1850 years earlier .
Simplified: Proper motion was not proved to exist until 1718 when Edmond Halley noticed the stars Sirius , Arcturus and Aldebaran had moved from the places they were in star charts that Hipparchus had drawn around 130 BC .