What astronomical phenomenon initially challenged the Ptolemaic geocentric model?
Answer
Planets sometimes appearing to move backward
The challenge began when astronomers observed that planets sometimes appeared to move backward across the night sky, which is known as retrograde motion.
Related Questions
To whom primarily belongs the credit for formulating the comprehensive mathematical model placing the Sun at the center?Which Greek astronomer most fully elaborated the geocentric model that dominated understanding for over a millennium?What astronomical phenomenon initially challenged the Ptolemaic geocentric model?What required intricate additions did the Ptolemaic system use to account for retrograde motion while keeping Earth central?What is the title of Nicolaus Copernicus’s revolutionary magnum opus?Besides rotation on its axis and revolution around the Sun, what third motion did Copernicus suggest the Earth possessed?What was the initial primary strength that made Copernicus's model superior to Ptolemy's for astronomers?What observable phenomenon, if detected, would have provided physical proof of the Earth's movement around the Sun?Which astronomer's subsequent telescopic observations provided direct evidence contradicting the Earth-centered model?What observation made by Galileo using the telescope proved Venus orbited the Sun?What discovery by Galileo demonstrated that not everything in the heavens orbited the Earth?In what year was Copernicus’s groundbreaking work on the heliocentric system published?